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How are railway engines designed?

The Diesel Locomotive The modern diesel locomotive is a self contained version of the electric locomotive. Like the electric locomotive, it has electric drive, in the form of traction motors driving the axles and controlled with electronic controls. It also has many of the same auxiliary systems for cooling, lighting, heating, braking and hotel power (if required) for the train. It can operate over the same routes (usually) and can be operated by the same drivers. It differs principally in that it carries its own generating station around with it, instead of being connected to a remote generating station through overhead wires or a third rail. The generating station consists of a large diesel engine coupled to an alternator producing the necessary electricity. A fuel tank is also essential. It is interesting to note that the modern diesel locomotive produces about 35% of the power of a electric locomotive of similar weight. The UK Class 47 is typical of the general purpose diesel-electric locomotives introduced in the 1960s. New SD90MAC 6,000 hp heavy freight US diesel-electric locomotives with AC drive first built in 1998 Click on an image for the full size view. Parts of a Diesel-Electric Locomotive The following diagram shows the main parts of a US-built diesel-electric locomotive. Click on the part name for a description. Diesel Engine This is the main power source for the locomotive. It comprises a large cylinder block, with the cylinders arranged in a straight line or in a V (see more ,here,). The engine rotates the drive shaft at up to 1,000 rpm and this drives the various items needed to power the locomotive. As the transmission is electric, the engine is used as the power source for the electricity generator or alternator, as it is called nowadays. Main Alternator The diesel engine drives the main alternator which provides the power to move the train. The alternator generates AC electricity which is used to provide power for the traction motors mounted on the trucks (bogies). In older locomotives, the alternator was a DC machine, called a generator. It produced direct current which was used to provide power for DC traction motors. Many of these machines are still in regular use. The next development was the replacement of the generator by the alternator but still using DC traction motors. The AC output is rectified to give the DC required for the motors. For more details on AC and DC traction, see the ,Electronic Power Page, on this site. Auxiliary Alternator Locomotives used to operate passenger trains are equipped with an auxiliary alternator. This provides AC power for lighting, heating, air conditioning, dining facilities etc. on the train. The output is transmitted along the train through an auxiliary power line. In the US, it is known as "head end power" or "hotel power". In the UK, air conditioned passenger coaches get what is called electric train supply (ETS) from the auxiliary alternator. Motor Blower The diesel engine also drives a motor blower. As its name suggests, the motor blower provides air which is blown over the traction motors to keep them cool during periods of heavy work. The blower is mounted inside the locomotive body but the motors are on the trucks, so the blower output is connected to each of the motors through flexible ducting. The blower output also cools the alternators. Some designs have separate blowers for the group of motors on each truck and others for the alternators. Whatever the arrangement, a modern locomotive has a complex air management system which monitors the temperature of the various rotating machines in the locomotive and adjusts the flow of air accordingly. Air Intakes The air for cooling the locomotive's motors is drawn in from outside the locomotive. It has to be filtered to remove dust and other impurities and its flow regulated by temperature, both inside and outside the locomotive. The air management system has to take account of the wide range of temperatures from the possible +40°C of summer to the possible -40°C of winter. Rectifiers/Inverters The output from the main alternator is AC but it can be used in a locomotive with either DC or AC traction motors. DC motors were the traditional type used for many years but, in the last 10 years, AC motors have become standard for new locomotives. They are cheaper to build and cost less to maintain and, with electronic management can be very finely controlled. To see more on the difference between DC and AC traction technology try the ,Electronic Power Page, on this site. To convert the AC output from the main alternator to DC, rectifiers are required. If the motors are DC, the output from the rectifiers is used directly. If the motors are AC, the DC output from the rectifiers is converted to 3-phase AC for the traction motors. In the US, there are some variations in how the inverters are configured. GM EMD relies on one inverter per truck, while GE uses one inverter per axle - both systems have their merits. EMD's system links the axles within each truck in parallel, ensuring wheel slip control is maximised among the axles equally. Parallel control also means even wheel wear even between axles. However, if one inverter (i.e. one truck) fails then the unit is only able to produce 50 per cent of its tractive effort. One inverter per axle is more complicated, but the GE view is that individual axle control can provide the best tractive effort. If an inverter fails, the tractive effort for that axle is lost, but full tractive effort is still available through the other five inverters. By controlling each axle individually, keeping wheel diameters closely matched for optimum performance is no longer necessary. ,This paragraph sourced from e-mail by unknown correspondent 3 November 1997., Electronic Controls Almost every part of the modern locomotive's equipment has some form of electronic control. These are usually collected in a control cubicle near the cab for easy access. The controls will usually include a maintenance management system of some sort which can be used to download data to a portable or hand-held computer. Control Stand This is the principal man-machine interface, known as a control desk in the UK or control stand in the US. The common US type of stand is positioned at an angle on the left side of the driving position and, it is said, is much preferred by drivers to the modern desk type of control layout usual in Europe and now being offered on some locomotives in the US. Cab The standard configuration of US-designed locomotives is to have a cab at one end of the locomotive only. Since most the US structure gauge is large enough to allow the locomotive to have a walkway on either side, there is enough visibility for the locomotive to be worked in reverse. However, it is normal for the locomotive to operate with the cab forwards. In the UK and many European countries, locomotives are full width to the structure gauge and cabs are therefore provided at both ends. Batteries Just like an automobile, the diesel engine needs a battery to start it and to provide electrical power for lights and controls when the engine is switched off and the alternator is not running. Traction Motor Since the diesel-electric locomotive uses electric transmission, traction motors are provided on the axles to give the final drive. These motors were traditionally DC but the development of modern power and control electronics has led to the introduction of 3-phase AC motors. For a description of how this technology works, go to the ,Electronic Power Page, on this site. There are between four and six motors on most diesel-electric locomotives. A modern AC motor with air blowing can provide up to 1,000 hp. Pinion/Gear The traction motor drives the axle through a reduction gear of a range between 3 to 1 (freight) and 4 to 1 (passenger). Fuel Tank A diesel locomotive has to carry its own fuel around with it and there has to be enough for a reasonable length of trip. The fuel tank is normally under the loco frame and will have a capacity of say 1,000 imperial gallons (UK Class 59, 3,000 hp) or 5,000 US gallons in a General Electric AC4400CW 4,400 hp locomotive. The new AC6000s have 5,500 gallon tanks. In addition to fuel, the locomotive will carry around, typically about 300 US gallons of cooling water and 250 gallons of lubricating oil for the diesel engine. Air Reservoirs Air reservoirs containing compressed air at high pressure are required for the train braking and some other systems on the locomotive. These are often mounted next to the fuel tank under the floor of the locomotive. Air Compressor The air compressor is required to provide a constant supply of compressed air for the locomotive and train brakes. In the US, it is standard practice to drive the compressor off the diesel engine drive shaft. In the UK, the compressor is usually electrically driven and can therefore be mounted anywhere. The Class 60 compressor is under the frame, whereas the Class 37 has the compressors in the nose. Drive Shaft The main output from the diesel engine is transmitted by the drive shaft to the alternators at one end and the radiator fans and compressor at the other end. Gear Box The radiator and its cooling fan is often located in the roof of the locomotive. Drive to the fan is therefore through a gearbox to change the direction of the drive upwards. Radiator and Radiator Fan The radiator works the same way as in an automobile. Water is distributed around the engine block to keep the temperature within the most efficient range for the engine. The water is cooled by passing it through a radiator blown by a fan driven by the diesel engine. See ,Cooling, for more information. Turbo Charging The amount of power obtained from a cylinder in a diesel engine depends on how much fuel can be burnt in it. The amount of fuel which can be burnt depends on the amount of air available in the cylinder. So, if you can get more air into the cylinder, more fuel will be burnt and you will get more power out of your ignition. Turbo charging is used to increase the amount of air pushed into each cylinder. The turbocharger is driven by exhaust gas from the engine. This gas drives a fan which, in turn, drives a small compressor which pushes the additional air into the cylinder. Turbocharging gives a 50% increase in engine power. The main advantage of the turbocharger is that it gives more power with no increase in fuel costs because it uses exhaust gas as drive power. It does need additional maintenance, however, so there are some type of lower power locomotives which are built without it. Sand Box Locomotives always carry sand to assist adhesion in bad rail conditions. Sand is not often provided on multiple unit trains because the adhesion requirements are lower and there are normally more driven axles. Truck Frame This is the part (called the bogie in the UK) carrying the wheels and traction motors of the locomotive. More information is available at the ,Bogie Parts Page, or the ,Wheels and Bogies Page, on this site. Wheel The best page for information on wheels is the ,Wheels and Bogies Page, on this site. Mechanical Transmission A diesel-mechanical locomotive is the simplest type of diesel locomotive. As the name suggests, a mechanical transmission on a diesel locomotive consists a direct mechanical link between the diesel engine and the wheels. In the example below, the diesel engine is in the 350-500 hp range and the transmission is similar to that of an automobile with a four speed gearbox. Most of the parts are similar to the diesel-electric locomotive but there are some variations in design mentioned below. Fluid Coupling In a diesel-mechanical transmission, the main drive shaft is coupled to the engine by a fluid coupling. This is a hydraulic clutch, consisting of a case filled with oil, a rotating disc with curved blades driven by the engine and another connected to the road wheels. As the engine turns the fan, the oil is driven by one disc towards the other. This turns under the force of the oil and thus turns the drive shaft. Of course, the start up is gradual until the fan speed is almost matched by the blades. The whole system acts like an automatic clutch to allow a graduated start for the locomotive. Gearbox This does the same job as that on an automobile. It varies the gear ratio between the engine and the road wheels so that the appropriate level of power can be applied to the wheels. Gear change is manual. There is no need for a separate clutch because the functions of a clutch are already provided in the fluid coupling. Final Drive The diesel-mechanical locomotive uses a final drive similar to that of a steam engine. The wheels are coupled to each other to provide more adhesion. The output from the 4-speed gearbox is coupled to a final drive and reversing gearbox which is provided with a transverse drive shaft and balance weights. This is connected to the driving wheels by connecting rods. Hydraulic Transmission Hydraulic transmission works on the same principal as the fluid coupling but it allows a wider range of "slip" between the engine and wheels. It is known as a "torque converter". When the train speed has increased sufficiently to match the engine speed, the fluid is drained out of the torque converter so that the engine is virtually coupled directly to the locomotive wheels. It is virtually direct because the coupling is usually a fluid coupling, to give some "slip". Higher speed locomotives use two or three torque converters in a sequence similar to gear changing in a mechanical transmission and some have used a combination of torque converters and gears. Some designs of diesel-hydraulic locomotives had two diesel engines and two transmission systems, one for each bogie. The design was poplar in Germany (the V200 series of locomotives, for example) in the 1950s and was imported into parts of the UK in the 1960s. However, it did not work well in heavy or express locomotive designs and has largely been replaced by diesel-electric transmission. Wheel Slip Wheels slip is the bane of the driver trying to get a train away smoothly. The tenuous contact between steel wheel and steel rail is one of the weakest parts of the railway system. Traditionally, the only cure has been a combination of the skill of the driver and the selective use of sand to improve the adhesion. Today, modern electronic control has produced a very effective answer to this age old problem. The system is called creep control. Extensive research into wheel slip showed that, even after a wheelset starts to slip, there is still a considerable amount of useable adhesion available for traction. The adhesion is available up to a peak, when it will rapidly fall away to an uncontrolled spin. Monitoring the early stages of slip can be used to adjust the power being applied to the wheels so that the adhesion is kept within the limits of the "creep" towards the peak level before the uncontrolled spin sets in. The slip is measured by detecting the locomotive speed by Doppler radar (instead of the usual method using the rotating wheels) and comparing it to the motor current to see if the wheel rotation matches the ground speed. If there is a disparity between the two, the motor current is adjusted to keep the slip within the "creep" range and keep the tractive effort at the maximum level possible under the creep conditions. Diesel Multiple Units (DMUs) The diesel engines used in DMUs work on exactly the same principles as those used in locomotives, except that the transmission is normally mechanical with some form of gear change system. DMU engines are smaller and several are used on a train, depending on the configuration. The diesel engine is often mounted under the car floor and on its side because of the restricted space available. Vibration being transmitted into the passenger saloon has always been a problem but some of the newer designs are very good in this respect. There are some diesel-electric DMUs around and these normally have a separate engine compartment containing the engine and the generator or alternator. The Diesel Engine The diesel engine was first patented by Dr Rudolf Diesel (1858-1913) in Germany in 1892 and he actually got a successful engine working by 1897. By 1913, when he died, his engine was in use on locomotives and he had set up a facility with Sulzer in Switzerland to manufacture them. His death was mysterious in that he simply disappeared from a ship taking him to London. The diesel engine is a compression-ignition engine, as opposed to the petrol (or gasoline) engine, which is a spark-ignition engine. The spark ignition engine uses an electrical spark from a "spark plug" to ignite the fuel in the engine's cylinders, whereas the fuel in the diesel engine's cylinders is ignited by the heat caused by air being suddenly compressed in the cylinder. At this stage, the air gets compressed into an area 1/25th of its original volume. This would be expressed as a compression ratio of 25 to 1. A compression ratio of 16 to 1 will give an air pressure of 500 lbs/in² (35.5 bar) and will increase the air temperature to over 800°F (427°C). The advantage of the diesel engine over the petrol engine is that it has a higher thermal capacity (it gets more work out of the fuel), the fuel is cheaper because it is less refined than petrol and it can do heavy work under extended periods of overload. It can however, in a high speed form, be sensitive to maintenance and noisy, which is why it is still not popular for passenger automobiles. Diesel Engine Types There are two types of diesel engine, the two-stroke engine and the four-stroke engine. As the names suggest, they differ in the number of movements of the piston required to complete each cycle of operation. The simplest is the two-stroke engine. It has no valves. The exhaust from the combustion and the air for the new stroke is drawn in through openings in the cylinder wall as the piston reaches the bottom of the downstroke. Compression and combustion occurs on the upstroke. As one might guess, there are twice as many revolutions for the two-stroke engine as for equivalent power in a four-stroke engine. The four-stroke engine works as follows: Downstroke 1 - air intake, upstroke 1 - compression, downstroke 2 - power, upstroke 2 - exhaust. Valves are required for air intake and exhaust, usually two for each. In this respect it is more similar to the modern petrol engine than the 2-stroke design. In the UK, both types of diesel engine were used but the 4-stroke became the standard. The UK Class 55 "Deltic" (not now in regular main line service) unusually had a two-stroke engine. In the US, the General Electric (GE) built locomotives have 4-stroke engines whereas General Motors (GM) always used 2-stroke engines until the introduction of their SD90MAC 6000 hp "H series" engine, which is a 4-stroke design. The reason for using one type or the other is really a question of preference. However, it can be said that the 2-stroke design is simpler than the 4-stroke but the 4-stroke engine is more fuel efficient. Size Does Count Basically, the more power you need, the bigger the engine has to be. Early diesel engines were less than 100 horse power (hp) but today the US is building 6000 hp locomotives. For a UK locomotive of 3,300 hp (Class 58), each cylinder will produce about 200 hp, and a modern engine can double this if the engine is ,turbocharged,. The maximum rotational speed of the engine when producing full power will be about 1000 rpm (revolutions per minute) and the engine will idle at about 400 rpm. These relatively low speeds mean that the engine design is heavy, as opposed to a high speed, lightweight engine. However, the UK HST (High Speed Train, developed in the 1970s) engine has a speed of 1,500 rpm and this is regarded as high speed in the railway diesel engine category. The slow, heavy engine used in railway locomotives will give low maintenance requirements and an extended life. There is a limit to the size of the engine which can be accommodated within the railway loading gauge, so the power of a single locomotive is limited. Where additional power is required, it has become usual to add locomotives. In the US, where freight trains run into tens of thousands of tons weight, four locomotives at the head of a train are common and several additional ones in the middle or at the end are not unusual. To V or not to V Diesel engines can be designed with the cylinders "in-line", "double banked" or in a "V". The double banked engine has two rows of cylinders in line. Most diesel locomotives now have V form engines. This means that the cylinders are split into two sets, with half forming one side of the V. A V8 engine has 4 cylinders set at an angle forming one side of the V with the other set of four forming the other side. The crankshaft, providing the drive, is at the base of the V. The V12 was a popular design used in the UK. In the US, V16 is usual for freight locomotives and there are some designs with V20 engines. Engines used for DMU (diesel multiple unit) trains in the UK are often mounted under the floor of the passenger cars. This restricts the design to in-line engines, which have to be mounted on their side to fit in the restricted space. An unusual engine design was the UK 3,300 hp Class 55 locomotive, which had the cylinders arranged in three sets of opposed Vs in an triangle, in the form of an upturned delta, hence the name "Deltic". Tractive Effort, Pull and Power Before going too much further, we need to understand the definitions of tractive effort, drawbar pull and power. The definition of tractive effort (TE) is simply the force exerted at the wheel rim of the locomotive and is usually expressed in pounds (lbs) or kilo Newtons (kN). By the time the tractive effort is transmitted to the coupling between the locomotive and the train, the drawbar pull, as it is called will have reduced because of the friction of the mechanical parts of the drive and some wind resistance. Power is expressed as horsepower (hp) or kilo Watts (kW) and is actually a rate of doing work. A unit of horsepower is defined as the work involved by a horse lifting 33,000 lbs one foot in one minute. In the metric system it is calculated as the power (Watts) needed when one Newton of force is moved one metre in one second. The formula is P = (F*d)/t where P is power, F is force, d is distance and t is time. One horsepower equals 746 Watts. The relationship between power and drawbar pull is that a low speed and a high drawbar pull can produce the same power as high speed and low drawbar pull. If you need to increase higher tractive effort and high speed, you need to increase the power. To get the variations needed by a locomotive to operate on the railway, you need to have a suitable means of transmission between the diesel engine and the wheels. One thing worth remembering is that the power produced by the diesel engine is not all available for traction. In a 2,580 hp diesel electric locomotive, some 450 hp is lost to on-board equipment like blowers, radiator fans, air compressors and "hotel power" for the train. Starting A diesel engine is started (like an automobile) by turning over the crankshaft until the cylinders "fire" or begin combustion. The starting can be done electrically or pneumatically. Pneumatic starting was used for some engines. Compressed air was pumped into the cylinders of the engine until it gained sufficient speed to allow ignition, then fuel was applied to fire the engine. The compressed air was supplied by a small auxiliary engine or by high pressure air cylinders carried by the locomotive. Electric starting is now standard. It works the same way as for an automobile, with batteries providing the power to turn a starter motor which turns over the main engine. In older locomotives fitted with DC generators instead of AC alternators, the generator was used as a starter motor by applying battery power to it. Governor Once a diesel engine is running, the engine speed is monitored and controlled through a governor. The governor ensures that the engine speed stays high enough to idle at the right speed and that the engine speed will not rise too high when full power is demanded. The governor is a simple mechanical device which first appeared on steam engines. It operates on a diesel engine as shown in the diagram below. The governor consists of a rotating shaft, which is driven by the diesel engine. A pair of flyweights are linked to the shaft and they rotate as it rotates. The centrifugal force caused by the rotation causes the weights to be thrown outwards as the speed of the shaft rises. If the speed falls the weights move inwards. The flyweights are linked to a collar fitted around the shaft by a pair of arms. As the weights move out, so the collar rises on the shaft. If the weights move inwards, the collar moves down the shaft. The movement of the collar is used to operate the fuel rack lever controlling the amount of fuel supplied to the engine by the injectors. Fuel Injection Ignition is a diesel engine is achieved by compressing air inside a cylinder until it gets very hot (say 400°C, almost 800°F) and then injecting a fine spray of fuel oil to cause a miniature explosion. The explosion forces down the piston in the cylinder and this turns the crankshaft. To get the fine spray needed for successful ignition the fuel has to be pumped into the cylinder at high pressure. The fuel pump is operated by a cam driven off the engine. The fuel is pumped into an injector, which gives the fine spray of fuel required in the cylinder for combustion. Fuel Control In an automobile engine, the power is controlled by the amount of fuel/air mixture applied to the cylinder. The mixture is mixed outside the cylinder and then applied by a throttle valve. In a diesel engine the amount of air applied to the cylinder is constant so power is regulated by varying the fuel input. The fine spray of fuel injected into each cylinder has to be regulated to achieve the amount of power required. Regulation is achieved by varying the fuel sent by the fuel pumps to the injectors. The control arrangement is shown in the diagram left. The amount of fuel being applied to the cylinders is varied by altering the effective delivery rate of the piston in the injector pumps. Each injector has its own pump, operated by an engine-driven cam, and the pumps are aligned in a row so that they can all be adjusted together. The adjustment is done by a toothed rack (called the "fuel rack") acting on a toothed section of the pump mechanism. As the fuel rack moves, so the toothed section of the pump rotates and provides a drive to move the pump piston round inside the pump. Moving the piston round, alters the size of the channel available inside the pump for fuel to pass through to the injector delivery pipe. The fuel rack can be moved either by the driver operating the power controller in the cab or by the governor. If the driver asks for more power, the control rod moves the fuel rack to set the pump pistons to allow more fuel to the injectors. The engine will increase power and the governor will monitor engine speed to ensure it does not go above the predetermined limit. The limits are fixed by springs (not shown) limiting the weight movement. Engine Control Development So far we have seen a simple example of diesel engine control but the systems used by most locomotives in service today are more sophisticated. To begin with, the drivers control was combined with the governor and hydraulic control was introduced. One type of governor uses oil to control the fuel racks hydraulically and another uses the fuel oil pumped by a gear pump driven by the engine. Some governors are also linked to the turbo charging system to ensure that fuel does not increase before enough turbocharged air is available. In the most modern systems, the governor is electronic and is part of a complete engine management system. Power Control The diesel engine in a diesel-electric locomotive provides the drive for the main alternator which, in turn, provides the power required for the traction motors. We can see from this therefore, that the power required from the diesel engine is related to the power required by the motors. So, if we want more power from the motors, we must get more current from the alternator so the engine needs to run faster to generate it. Therefore, to get the optimum performance from the locomotive, we must link the control of the diesel engine to the power demands being made on the alternator. In the days of generators, a complex electro-mechanical system was developed to achieve the feedback required to regulate engine speed according to generator demand. The core of the system was a load regulator, basically a variable resistor which was used to very the excitation of the generator so that its output matched engine speed. The control sequence (simplified) was as follows: 1. Driver moves the power controller to the full power position 2. An air operated piston actuated by the controller moves a lever, which closes a switch to supply a low voltage to the load regulator motor. 3. The load regulator motor moves the variable resistor to increase the main generator field strength and therefore its output. 4. The load on the engine increases so its speed falls and the governor detects the reduced speed. 5. The governor weights drop and cause the fuel rack servo system to actuate. 6. The fuel rack moves to increase the fuel supplied to the injectors and therefore the power from the engine. 7. The lever (mentioned in 2 above) is used to reduce the pressure of the governor spring. 8. When the engine has responded to the new control and governor settings, it and the generator will be producing more power. On locomotives with an alternator, the load regulation is done electronically. Engine speed is measured like modern speedometers, by counting the frequency of the gear teeth driven by the engine, in this case, the starter motor gearwheel. Electrical control of the fuel injection is another improvement now adopted for modern engines. Overheating can be controlled by electronic monitoring of coolant temperature and regulating the engine power accordingly. Oil pressure can be monitored and used to regulate the engine power in a similar way. Cooling Like an automobile engine, the diesel engine needs to work at an optimum temperature for best efficiency. When it starts, it is too cold and, when working, it must not be allowed to get too hot. To keep the temperature stable, a cooling system is provided. This consists of a water-based coolant circulating around the engine block, the coolant being kept cool by passing it through a radiator. The coolant is pumped round the cylinder block and the radiator by an electrically or belt driven pump. The temperature is monitored by a thermostat and this regulates the speed of the (electric or hydraulic) radiator fan motor to adjust the cooling rate. When starting the coolant isn't circulated at all. After all, you want the temperature to rise as fast as possible when starting on a cold morning and this will not happen if you a blowing cold air into your radiator. Some radiators are provided with shutters to help regulate the temperature in cold conditions. If the fan is driven by a belt or mechanical link, it is driven through a fluid coupling to ensure that no damage is caused by sudden changes in engine speed. The fan works the same way as in an automobile, the air blown by the fan being used to cool the water in the radiator. Some engines have fans with an electrically or hydrostatically driven motor. An hydraulic motor uses oil under pressure which has to be contained in a special reservoir and pumped to the motor. It has the advantage of providing an in-built fluid coupling. A problem with engine cooling is cold weather. Water freezes at 0°C or 32°F and frozen cooling water will quickly split a pipe or engine block due to the expansion of the water as it freezes. Some systems are "self draining" when the engine is stopped and most in Europe are designed to use a mixture of anti-freeze, with Gycol and some form of rust inhibitor. In the US, engines do not normally contain anti-freeze, although the new GM EMD "H" engines are designed to use it. Problems with leaks and seals and the expense of putting a 100 gallons (378.5 litres) of coolant into a 3,000 hp engine, means that engines in the US have traditionally operated without it. In cold weather, the engine is left running or the locomotive is kept warm by putting it into a heated building or by plugging in a shore supply. Another reason for keeping diesel engines running is that the constant heating and cooling caused by shutdowns and restarts, causes stresses in the block and pipes and tends to produce leaks. Lubrication Like an automobile engine, a diesel engine needs lubrication. In an arrangement similar to the engine cooling system, lubricating oil is distributed around the engine to the cylinders, crankshaft and other moving parts. There is a reservoir of oil, usually carried in the sump, which has to be kept topped up, and a pump to keep the oil circulating evenly around the engine. The oil gets heated by its passage around the engine and has to be kept cool, so it is passed through a radiator during its journey. The radiator is sometimes designed as a heat exchanger, where the oil passes through pipes encased in a water tank which is connected to the engine cooling system. The oil has to be filtered to remove impurities and it has to be monitored for low pressure. If oil pressure falls to a level which could cause the engine to seize up, a "low oil pressure switch" will shut down the engine. There is also a high pressure relief valve, to drain off excess oil back to the sump. Transmissions Like an automobile, a diesel locomotive cannot start itself directly from a stand. It will not develop maximum power at idling speed, so it needs some form of transmission system to multiply torque when starting. It will also be necessary to vary the power applied according to the train weight or the line gradient. There are three methods of doing this: mechanical, hydraulic or electric. Most diesel locomotives use electric transmission and are called "diesel-electric" locomotives. Mechanical and hydraulic transmissions are still used but are more common on multiple unit trains or lighter locomotives. Diesel-Electric Types Diesel-electric locomotives come in three varieties, according to the period in which they were designed. These three are: DC - DC (DC generator supplying DC traction motors); AC - DC (AC alternator output rectified to supply DC motors) and AC - DC - AC (AC alternator output rectified to DC and then inverted to 3-phase AC for the traction motors). The DC - DC type has a generator supplying the DC traction motors through a resistance control system, the AC - DC type has an alternator producing AC current which is rectified to DC and then supplied to the DC traction motors and, finally, the most modern has the AC alternator output being rectified to DC and then converted to AC (3-phase) so that it can power the 3-phase AC traction motors. Although this last system might seem the most complex, the gains from using AC motors far outweigh the apparent complexity of the system. In reality, most of the equipment uses solid state power electronics with microprocessor-based controls. For more details on AC and DC traction, see the ,Electronic Power Page, on this site. In the US, traction alternators (AC) were introduced with the 3000 hp single diesel engine locomotives, the first being the Alco C630. The SD40, SD45 and GP40 also had traction alternators only. On the GP38, SD38, GP39, and SD39s, traction generators (DC) were standard, and traction alternators were optional, until the dash-2 era, when they became standard. It was a similar story at General Electric. There is one traction alternator (or generator) per diesel engine in a locomotive (standard North American practice anyway). The Alco C628 was the last locomotive to lead the horsepower race with a DC traction alternator. Below is a diagram showing the main parts of a common US-built diesel-electric locomotive. I have used the US example because of the large number of countries which use them. There are obviously many variations in layout and European practice differs in many ways and we will note some of these in passing. More Information This page is just a brief description of the main points of interest concerning diesel locomotives. There aren't too many technical sites around but the following links give some useful information: ,US Diesel Loco Operating Manuals, - Copies of some of the older US diesel locomotive manuals issued to staff. Contains some very interesting details. ,Diesel-Electric and Electric Locomotives, - by Steve Sconfienza, PhD.D. - >Includes some technical background on the development of diesel and electric traction in the US, an illustration of the PRR catenary system and some electrical formulae related to different traction systems. ,Diesel-Electric Locomotive Operation, - A general list of US diesel locomotive types, designs and statistics with a summary of their development. A useful introduction to the US diesel loco scene.

What does bypass in plane engine terminology mean and why is it important?

It’s part of the description of an engine that gives a quick overall idea of the engine’s design and layout, much like you might describe a car engine as a ‘4 liter twin-turbo overhead cam V8’; there’s a lot more to the engine’s design that that, but that short phrase tells you the essentials. The first jet engines were what we would now call ‘turbojets’; they are fairly simple things that sucked fresh air in at the front, added some fuel and burned it in the middle, and then shot all the resulting hot exhaust gases out of the back, creating thrust. Although this works, it’s not very efficient; you can get lots of thrust, but you have to burn a lot of fuel to get it. A later development was to add a large fan on to the front of the engine to accelerate air around the sides of the central engine core, creating lots of additional thrust. As shown in the image above, the air that goes around the outside of the engine core is called ‘bypass air’. You can design your engine to have a relatively small fan, to make a ‘low bypass engine’, or with a big fan, to make a ‘high bypass engine’. The diagrams above came from: How Does A Turbofan Engine Work? which is just one of many sites that answer this question.

What are some of the best interview questions asked for a mechanical engineering student?

I'm sharing this question list to fellow mechanical engineers that I made to prepare for an interview. It contains two sections viz. technical questions followed by HR questions. 1. Technical questions:, Type of technical questions asked will be definition type and that too from basic. Your favorite subjects will be asked first and then they start questioning what they want you to answer.Some of the questions are... 1. Why we do not use same technology to start both SI/CI engine? 2. Which one is more efficient? A four stroke engine or a two stroke and why? 3. 4 Stroke engine is more efficient primarily Because of the presence of valves which precisely control the flow of charge into the chamber and exit the exhaust gases with proper timing which is hard to achieve by ports in a 2 stroke engine. 4. Why there is no differential in a train. What happens when a train takes a turn? 5. A cantilever beam is loaded a point on its ends what will be the effect in shear force? 6. Why vehicle does not move when its gear is applied though parked in slope area? 7. What is shear force in fluid particle? 8. How gear ratio helps in power variation? 9. What is the angle of twist in drill? 10. What is the difference between impact force and sudden force? 11. How to calculate the turbine efficiency? 12. Why centrifugal pump casing is called involutes casing? 13. What will happen if reciprocating compressor run in exactly opposite direction? 14. What is the effect of clearance volume in performance of air- compressor? 15. What is the advantages and disadvantages of critical speed of turbine? 16. What will happen if oil is mixed with boiler feed water? 17. What is difference between fan and blowers? 18. What are the protections required to protect turbine? 19. what is critical temperature? 20. Air is a bad conductor of heat. Why it becomes hot in summer? 21. How many stages in compressor in there in gas turbine? 22. Which is more efficient? A rear engine Volvo Bus or a Front engine Volvo Bus? (Engine Capacity is same for both) why? 23. What is difference between stress and pressure? 24. What is Boiler HP? 25. What is Auto Dosing? 26. What happens when too much oil is injected in the working cylinder? 27. How many manholes should be there on boiler? Why? 28. What is used to check the amount & quality of fuel in two stroke IC engine? 29. Work done in throttling process is given by which formula? 30. Function of the strainer in IC engine? 31. What is the difference between the air pre-heater & air blower? 32. Why the compression ratio of the diesel engine should be high? 33. A vertical plate and a horizontal plate are suspended in an open room. Both are heated to the same temperature. Which one will cool first? Why? 34. What is the color of flame if the boiler is running? 35. Which is the best lubricant-air, oil or water? 36. Tell the octane number in Indian petrol? 37. Difference between enthalpy & entropy? 38. What is the difference between safety valve and relief valve? 39. Explain cooling and its types? 40. What is the working principal of air compressor? 41. What is cryogenics and what are its fundamentals? 42. What is the difference between a shaper machine and a planner machine? 43. Why stress relieving of stainless steel is not proffered? 44. What are the advantages of PID controllers compared with those of a PLC? 45. Which two continents are mirror images of each other? 46. Where half nut is used? 47. What is the need for drafting? 48. Turbo charger driven by.............? and what its speed 49. Why...? Turbo charger used in DG....? 50. The stage below saturation is called? 51. Why is a condenser used in a Rankin cycle? 52. What is servo motor? 53. Can we use light duty vehicle axle into the heavy duty machinery axle? If no then why? 54. Stress strain diagram for fluid? 55. Where manning formula used? 56. What is level of documentations for a ISO 9001 certified company? 57. What is back plate in centrifugal pumps and its purpose? 58. Why tyres are manufactured in black colour? 59. Whether ductile material can fail in brittle manner? When? 60. On what property u can distinguish material as brittle or ductile? 61. Name fuels used in nuclear power plant? 62. On what thermodynamic cycle nuclear power plant works? 63. How can you increase the efficiency of power plant without changing in effort? 64. What is purpose of governor in Diesel engine? 65. Why petrol engines have more power than diesel engines of same capacity? 66. What is the difference between Torque and Power ( layman Idea)? 67. What will be the induced stress in the bar? 68. What is the Difference between Rated Speed and Economic Speed? 69. How to convert from HP to BHP or CC to Bhp please explain???????? 70. How the material no. 2062 will mild steel of density 7.85? What are the other codes? 71. Why petrol engine gives more power than diesel engine even though diesel engine has high compression ratio? 72. What is mean by Resistance welding? 73. Compare Brayton and Otto cycle. 74. Why we have to know the specific frequency of any equipment? does anybody know about specific frequency ? 75. What is pulverization? 76. What is the function of an isolator? 77. Why the back wheel of tractor is bigger than front wheel? 78. Flow will increase or decrease or remain same? 79. Why Mechanical seal used in Pumps? 80. The ratio of Emissive to absorption power of heat by a body is equal to heat emitted by a perfect black body. Who said the statement 81. What is colour of flame if the of Halide Torch detects a refrigerant leakage? 82. How can we remove paint from (painted over)plastic or nylon objects with out damaging the object? 83. How to calculate or arrive the capacity of a mechanical press? 84. The property of a metal that is determined by the indentation on a metal surface 85. The amount of thickness of the metal sheet that can be welded by ultrasonic welding is? 86. The amount of carbon present in Cast Iron? 87. Numeric control is used for? 88. The amount of moisture that is to be present in wood to be called dry wood is? 89. The pattern material used in Investment casting Process is? 90. What is the use of offset follower in cam? Why and where we have to use this type of follower? 91. What is the use of offset follower in cam? Why and where we have to use this type of follower? 92. State the difference between Forging & Fabrication? 93. What is flange rating? 94. What amount of heat energy loss in ESP? 95. What happen when diesel is injected in petrol engine? 96. What do you mean by property of system? 97. Why joule-Brayton cycle is not suitable for a reciprocating engine. 98. How does “turbulence” differ from swirl? 99. Is octane number beyond 100 is possible? 100. Explain the effect of fuel structure on knocking. 101. Discuss the advantages and disadvantages of LPG as a fuel in S.I. Engine? 102. What is the impact of using throttling device instead of expander in vapour compression cycle? 103. What is moisture choking? Which refrigerants are more prone to it? 104. What is Montreal protocol and why CFCs are being phased out? 105. Why reverse Joule Brayton is used in aircraft refrigeration system? 106. Explain how solar-energy can used in refrigeration system? 107. Is wet bulb temperature a thermodynamic property? 108. What is the utility of comfort chart? 109. How would you decide whether a reciprocating compressor or centrifugal compression is to be used in a refrigerating system? 110. Why smoking is not allowed in air conditioned enclosure? 111. Why desert coolers become ineffective in raining season? 112. Why package units are being preferred over central air conditioning system? 113. What is MAPI. 114. What is capital budgetary? 115. What is group technology layout? 116. What is leveling & smoothing in production technology? 117. What is deference between method study & work measurement? 118. What you know about drilling? 119. How oil is produced? What is the size of well? 120. Pumps used in drilling procedure and why? Why not centrifugal pump? What if we want high head and high discharge? 121. Difference between Pipeline and Piping ? 122. Use of CNG, LNG, LPG etc. ,Additional questions subject wise: Fluid Mechanics and Fluid Machinery What is the difference between impulse & reaction turbine. Explain unit speed, unit discharge unit power & specific speed. Explain NPSH, in which parameter it depends on. What is jet ratio? What is Deriaz turbine? Which turbine is good for tidal power plant? What is Navier-stroke equation. What are the significance of Mach number Weber number Material Science What is quazi-crystal? What do you understand by a free cutting steel? What elements are usually added to make a steel free cutting, & how they make the steel free cutting? Explain various method of hardening of steel? What do you understand by the term “Arrest point” in connecting with heat treatment of plain carbon steel? What influence does grain size have on the mechanical properties of metals. Describe the difference between brittle and ductile fracture. What is the difference between natural & artificial aging? Thermodynamics What is availability function for a closed system? If it is possible that entropy of a system can decrease during a given process? What is dead state in thermodynamics? What is exergy? What happens to triple point line when projected to P-T plane? What is compressibility factor and what is its value for Vander walls gases. What are initial conditions for formation of shock waves? What do you understand by choking in nozzle flows? Is it possible that pressure and velocity decreases simultaneously/ Distinguish between “Available energy” & Availability? What is pure substances. What is critical point? What is the value f critical temperature, pressure & volume of water? What is sublimation curve, fusion curve & vaporization curve? What is Rayleigh Line & Fanno Line? What is normal shocks & when its occurs? What is High Grade Energy & Low Grade Energy? Heat & Mass Transfer What is Newton’s Law of cooling. What is Recuperator & Regenerators? Whether fin can actually reduce heat transfer? is it possible? When? What is difference between Biot no. & Nusselt no? Which one is greater, thermal boundary layer or hydrodynamic boundary layer? What is film temperature in forced convection flow? What is fully developed region and where it is applicable? What is the critical radius of insulation, explain clearly in terms of thermal resistance and heat transfer rate? At what case do you recommend Fin? What is the difference between free convection & forced convection in what parameter forced & free convection depend. Internal Combustion Engine What is the use of Carburetor in SI Engine, There is trend towards increases of injection system in Automobiles, Explain. Why Supercharging is not popular with SI Engines? What is performance number. Explain Knocking in SI Engine & Mention, the factor that tend to reduce Knocking? Explain the difference between Knocking in SI Engine & CI Engine? How does “Turbulence” differ from “Swirl”? Name some Antiknock additive and explain the Mechanism by which they reduce the knock? Power Plant engineering What is slip ratio in thermal power plant? In Pendant super heater whether parallel flow or counter flow heat exchange between steam and flue gases. What happens to mass flow in case of supersaturated flow? Why clearance are provided in reciprocating compressor? Explain turbojet & Rocket Engine. What’s the advantage of compounding of steam turbine? What’s are boiler mounting & accessory. Draw the sketch of pulse jet engine. What are its main advantage & disadvantage? Explain working principal of scram jet engine, what is advantage over the ramjet? What are the advantage of nuclear power plants over thermal power plants. What is fast breeder reactor? What is circulation ratio and what is its range in power plant? One 2-row Curtis turbine is equivalent to how many reaction turbines for same value of blade velocity and angle of nozzle? What are thermal neutrons? What is breeding ratio? What is the application of jet and rocket technology? Which is used in missiles? Strength of Materials What do you mean by equal strength in a beam? What is difference between pure shear and simple (normal) shear? Is it possible that decrease in area gives a decrease in stress? Whether shear stresses are always parallel to shear forces? By which experiment, you find it toughness of material. Distinguish between direct stress & bending stress. What do you mean by Torsional rigidity & lateral rigidity? Define “slenderness ratio”. How it is used in long and short column? Machine Design What are rolling contact bearing? What are the anti friction bearings? What is stress concentration factor? What is the bolt of uniform strength? What is the difference Static Load carrying capacity & Dynamic Load carrying capacity? Why we are not using the unit joule for torque instead of N-m. What is Low cycle fatigue failure and High cycle fatigue failure? What are considerations of these while designing a machine? What is mechanical advantage? How trains take turns though there is no differential gear? Do you know epicyclical gear box? What is the practical application of epicyclical gear box? What is tooth profile? Which one is better? Theory of Machines What is Keneddy theorem? Do we need a screw with efficiency less than 50%? What is backlash? What is damping ratio? Define Resonance. Define critical speed or whirling speed or whipping speed. What is machine? Giving example, Differentiate between a machine & structure. What is Mechanical advantage. Refrigeration and Air-conditioning What is utility of comfort chart? hat is wet compression? To maximize COP what should be the condition of vapour at suction to compression? What is the range of NBP (normal boiling point) in case of most refrigerants? Why COP of CO2 gas is less and still why it is used in transport refrigeration? What are the most crucial parts in reciprocating compressors? How compressors are selected based on type of refrigerant? What is correlation between wet bulb temperatures an adiabatic saturation temperature? Why isothermal compressor is Desirable? What is desirable property of ideal refrigerant? Define effective temperature & what is the optimum design condition for comfort for summer A/C? Production Engineering Why arc is slowly extinguished in case of arc welding? Which inert gas is commonly used for thin work piece and which inert gas for thick work piece? What is friction welding? What is difference between brazing & braze welding? Why hole basis system is adopted in manufacturing? What is 3- 2-1 principle? Where diamond pin locator is used? How presses are rated? What is spring back? What is difference between fillet and corner radius? What are overhead costs? Why depreciation is to be taken into account in industrial management? Why breakeven point is important in any industry? What is sine bar? What is marginal cost and marginal revenue? What is shear and where it is provided in case of punching and blanking? What is angle of bite? What is extrusion ratio? What is gutter and where it is used? Which process is used for making nuclear reactor fuel rods? What is difference between Amorphous and crystalline solids? What are the various method of inspection of casting for internal & external defects? Why are allowances provided for in the production of patterns? What do they depend on? What is the deference between soldering & brazing? What is meant by solid-state welding explain. What is cold welding? Describe the principal behind resistance welding processes. What function should a lubricant perform in manufacturing process? Explain the difference between punching & blanking. Explain the difference between discontinuous chips and segment chips. Explain the different type of tool wear. What is difference between oblique & orthogonal cutting. What are the main difference between jig and fixture? What is AOQ What is LTPD What is Producer risk What is Consumer’s risk What is JIT approaches? What is group technology? What are its main advantages? Define the term “production & productivity. What is the significance of ISO 9000 series & 1400 series. What is artificial intelligence? Which welding process does not required any filler material? What is tack weld? Which process used for cutting thicker plates? Where drooping characteristics of power source is required in arc welding? 2. HR questions: Tell me about yourself? What is your hometown famous for? Tell about your achievements in life. Your strengths and weakness Are you a team player? Tell me about your ability to work under pressure. How would you know you will be successful on this job? Describe your management style. Global warming Chief justice of India Vice President of India CEO of Apple, when did he die? Gas scenario RBI policy Corporate Governance Corporate Laws Cast system is boon or bane ? What’s the difference in the modus operandi of Amir Khan’s “Satyameva jayate” and Anna Hazares movement? What will u do on your part to remove corruption? If you travel in a train without confirmed ticket will u bribe the TT for a seat? What do u mean by optimistic. Is it always good to be optimistic or it helps sometimes to be pessimist? What is difference between confidence and over confidence? What is the difference between hard work and smart work? What are your goals? What motivates you to do a good job? What makes you angry? Give an example of your creativity Describe ideal company, job, and location? What are your hobbies? Inspiration in your life and why? What was the toughest decision you ever had to make? Define success? and how do you measure up to your definition About present job (if employed) Why did you resign from your previous job? Why have you been unemployed so long? What was the toughest challenge you have ever faced? What would you say to your boss if he is crazy about an idea, but you think it stinks? Why should I hire you? Explain how you would be an asset to this organisation. If we give you a job will you leave IIT B or your organisation? What changes would you make if you came on board? Thanks Akshay.

I want to know everything about bikes. How do they work? What should be looked for before categorizing them into good and bad? What are cc, strokes, etc.?

In this answer I will be trying to make you understand the terms which you are going to face often on the web pages of different motorcycles. 4 Stroke Engine, A 4 stroke engine is the one in which the piston completes four separate strokes while turning a crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. 4 strokes can be categorized as following : (Please refer to this animation as I couldn't incorporate it in my answer ,Four-stroke engine, ) Intake: Open the intake valve(right one in the following diag.) so that air fuel mixture can come into the chamber. Compression: Compress the air fuel mixture. Power: While the mixture is fully compressed and piston is at its top most position, ignite the mixture using spark plug.Ignition leads to expansion of air-fuel mixture and thus forces the piston down to its bottom most position. Expansion: Exhaust valve (left one in above diag.) is opened and the piston forces the residual air-fuel mixture out of the chamber. These days all bike engines are of 4 strokes so their is no need to get further into it. Let's start focusing on more important aspects. 4 Valve and 2 Valve, In above diag. you can see there is one valve present for intake and one valve for exhaust of air fuel mixture hence the term 2 valve engine. In a 4 valve engine, there are 2 intake valves and 2 exhaust valves. Just as when you run at fast speeds you start taking breath from mouth as well, having 2 extra valves will help engine to get air-fuel mixture in sufficient amounts at higher rpms. Sports bike like R15 and CBR have 4 valve engine whereas 2 valve engines are more common in street bikes. SOHC and DOHC, In the engine diagram shown above, just above the rods attached to intake and exhaust valves, you can see two rotating pieces having a bulge outside. This mechanical piece is known as Cam and the bulge present at its surface helps to open and close the intake and exhaust valves just at right moments. Both cams used to be attached to a single rotating shaft, known as Camshaft, as shown in the following diagram. Fig. 1: The two bulgy pieces are Cams and the whole structure of cams and shaft/rod going through them is called Camshaft. Orange pieces are the rods connecting intake and exhaust valves. (Refer ,Camshaft, for complete animation) In a 2 valve engine a single camshaft is enough to open and close intake and exhaust valves by placing the cams at appropriate angles. Things get complicated in a 4 valve engine. There are two options to circumvent this problem : i) Use two camshafts, each camshaft having 2 cams for 2 inatke valves and other camshaft having cams for 2 exhaust valves. ii) Use single camshaft alongwith more complicated mechanism to operate all 4 valves. Hence, the name dervied are : SOHC : Single Overhead Camshaft DOHC : Double Overhead Camshaft Fig 2: 2 Valve SOHC Engine ( Image source ,Motorcycle Specifications, ) Fig 3: 2 Valve DOHC Engine ( Image source ,Motorcycle Specifications, ) As the camshafts are present just directly at the head of the engine, hence the name Overhead. Just to avoid any confusion, camshafts are present outside the engine but just above its head. DOHC layout has better valve opening and closing timings and more precise also but increases the weight and number of moving parts in engine. SOHC although will be lighter but we will have to use rocker arms to control the valves. CBR has 4 valve DOHC engine while R15 has 4 valve SOHC engine. 2 valve engine bikes have usual SOHC. Spark Plug, Position of spark plug plays key role in the efficient combustion of air-fuel mixture, as the ignition should spread evenly in the chamber. A 4 valve DOHC engine offers very favourable top central position for spark plug. In case of 4 valve SOHC engine, due to single camshaft present at top central position, spark plug is placed slightly away from this key position. Fig 4: 4 Valve DOHC Engine with spark plug in the middle of 4 vlaves (Image source ,http://www.caranddriver.com, ) Bajaj has been using DTSi technology which use two spark plugs instead of one for more efficient combustion although other key players are able to give equivalent benefits using only single spark plug. Air Cooled and Liquid Cooled, Air cooled engines are cooled naturally by outside air. They generally have fins present to dissipate more heat. Fig 5: Air cooled engine. (Image source ,http://zxj510228.en.ec21.com, ) Liquid cooled engine is surrounded by a continusouly flowing coolant which absorbs the heat and dissipate it at the radiator. Liquid cooling is used in the engines having high compression ratio, which can operate at high rpms as sports bike. Fig 6: Liquid cooled engine (Image source ,http://www.iamabiker.com, ) R15 and CBR use liquid cooled engine as opposed to air cooled engine in FZS, Gixxer, etc. Max Power and Max Torque, These parameters are of great importance to look out for while comparing motorcycles but they are very hard to understand and quite confusing. I am incorporating few words from this article ,http://www.bikesindia.org/reviews/difference-between-motorcycle-power-torque-explained-which-is-better.html, Power:, The Power produced by any engine is the capacity of that engine to take the motorcycle to its maximum speed. Torque:, The Torque generated by an engine is an entity which determines the pulling capacity of the bike. You will have to dive deep into this topic on your own. Displacement, As given on Wikipedia, engine displacement is the volume swept by the piston inside the cylinder of engine in a single movement from top dead centre (topmost position) to bottom dead centre (bottommost position), commonly specified in cubic centimeters(cc). Generally higher the displacement higher the torque and power you get. But there is no direct relationship between displacement and power. For example Honda CB Trigger with 150cc engine given max power of 14 bhp whereas Honda CBR 150R with 150cc engine gives max power of 18 bhp. So instead of looking just at displacement, give more weightage to maximum torque and maximum power the engine can deliver. Disc Brake and Drum Brake, In a disc brake, the brake pads squeeze the disc attached instead of the wheel, and the force is transmitted hydraulically instead of through a cable. Friction between the pads and the disc slows the disc down. Fig 7: Working of disc brake ( Image source ,http://auto.howstuffworks.com,) In drum brake set of shoes or pads press outward against a rotating cylinder-shaped part called brake drum. Disc brakes are superior to drum brakes in stopping vehicle, they dissipate heat better and also have less wear and tear. General trend is to have disc brakes in front, as momentum is transferred to the from while stopping, and drum brakes in rear due to cost constraints. High end bikes have disc brakes in both front and rear. Fuel Injection and Carburetor, Constant supply of air-fuel mixture in right proportions and in right amount to engine is of upmost importance and the amount should be adaptable according to the factors like the speed at which engine is running, load, etc. Before the advent of modern electronic sensors, this task was handled by a mechanical device called Carburetor. Fig 8: Carburetor (Image source ,http://www.rc-trucks.org,) Now days, carburetors are replaced with electronic Fuel Injection systems which gather engine operation information using various sensors and then decide the control over the air-fuel mixture. Carburetor are still popular in motorcycles and there is a heated debate between which one to use. Carburetors can be diagnosed by a mechanic in case you got unlucky in some remote area and their performance have been quite satisfactory until now. Fuel injection systems provide better fuel efficiency and power but to what extent is a topic of debate. Also if you got unlucky with fuel injection system in a remote area, then there is not much that you can do. There are lot of other factors which you can find on internet. Twinshock and Monoshock Rear Suspension, For rear suspension generally Twinshock absorbers are used but they add additional weight and get bendy and flexible in extreme riding conditions. Fig 9: Simplified view of twinshock absorber ( Image source ,The Car Maintenance Bibles, ) These problems can be overcomed by the use of Monoshock absorbers. Fig 10: Monoshock absorber ( Image source ,BikeAdvice.in,) Monoshock are more popular with high end sports bike and Twinshock with general street bikes. Full Fairing and Half Fairing, A motorcycle fairing is a shell placed over the fame of some motorcycles with primary purpose to reduce air drag. Full fairings cover both upper and lower portions of motorcycles, as distinct from a half fairing, which only has an upper section, and leaves the lower half of the motorcycle exposed. Fig 11: Full fairing, most portion of engine gets hidden behind the fairing. (Image source ,http://sv1000.lsn.net, ) Fig 12: Semi faired version of Karizma. (Image source ,Top Speed In,) Kerb Weight, Kerb weight is the total weight of a vehicle with standard equipment, all necessary operating consumables such as motor oil, transmission oil, coolant, air conditioning refrigerant, and a full tank of fuel, while not loaded with either passengers or cargo. So lesser the kerb weight more performance engine can provide. Wheelbase, Wheelbase is the distance between the centers of the front and rear wheels. Well the shorter it is the quicker a bike can turn and the longer it is the more stable it will be. That is why criusers like Bajaj Avenger have much greater wheelbase compared to other street and sports bikes. Fig 13: (Image source ,http://www.carbibles.com, ) More motorcycle geometry and handling factors can be read at ,Motorcycle Geometry 101,. Tubeless Tyres, Tubeless tyres do not require a separate inner tube and hence light weight and air leakage is slower in case of puncture. You can cover few more kilometers on motorcycle itself once tyre gets punctured. At the end of my answer, I will say that although the features described above play key role, factors which cannot be described but rather can only be experienced are handling, comfort, easiness in shifting gears, engine vibrations, noise and many more. I will also not recommend you to maximize the features described above as that will lead you only to Sports Bikes. Instead, first the select category from which you want your bike to be and then you can sort according to the above parameters. Bikes are broadly categorized as : Street Cruiser Sports Happy Hunting !!