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## otto cycle ideal gas Post Review

Always assume ideal gas in Otto Cycle, they saidCv=(5/2)R, they said

"It's left to the reader to corroborate that for an ideal gas with temperature independent heat capacities, the Otto Cycle efficiency is(...)"

otto cycle kena tengok table A-17 , ideal gas properties. (Y)

Masih berpusing2 dg IdeaL Gas Turbine, Otto cycLe, dan DieseL CycLe...,yuk,.itung...itung.-itung.! *Semangat mode On :D :D

## otto cycle ideal gas Q&A Review

### How do diesel engines run without spark plugs?

All the answers look good, but let me inject some basic textbook concepts. The traditional gasoline engine is an Otto Cycle engine, named after Nikolaus Otto. The diesel engine, named after Rudolf Diesel, uses the Diesel Cycle. The ,cycles, in these cases refer to a graph of pressure versus volume as one cylinder goes through its 2 or 4 strokes and is ready to repeat. In the idealized Otto Cycle, air is compressed, then heat is added quickly--at constant volume--when the spark plug detonates the mixture. The heat raises the pressure, so that work will be done as the heated air expands in the power stroke. In the idealized diesel cycle, the compressed air is hot enough to start combustion, then the fuel is added over a non-zero time during the power stroke so that the gas is heated at constant pressure during part of the power stroke. To an engineer, the idealized cycle defines each type of engine. When the air in the cylinder is hot enough to ignite the diesel fuel, then the time of fuel burning is controlled by the time during which the injector sprays a mist of fuel. The Otto cycle calls for quick burning, so the air and fuel can be pre-mixed, ready to burn ASAP when the spark plug sparks. If you can gradually absorb the idea of the idealized cycles, then you can read Wikipedia articles on different interesting engines. For example, some current Ford hybrid cars have Atkinson-cycle engines. They are like Otto cycle engines, but less air is taken in during the cycle, which raises efficiency. Wikipedia has an article called ,Heat engine, which will give you links to other articles on specific idealized cycles. Traditional Otto Cycle engines depend on keeping the air/gasoline ratio in a range where the flame will propagate after it's ignited by the spark. In diesel engines, the air/fuel ratio is not a critical parameter in the same way. Of course more recent gasoline engines use new technologies to bend the old rules and save fuel.

### How is the actual P-V diagram of a 4 stroke SI engine different from the theoretical one?

It is not very different if you do Finite heat transfer model (Thermally variable properties). If you compare with Otto cycle directly, there are tons of differences as that's no way realistic (ideal gas, Constant properties, uniform composition etc.). But I did experiments with the variable property models and they are very alike (for ensemble averaged characteristics).

### What is difference between otto and diesel cycle?

In simplest terms the Otto cycle is an internal combustion engine that compresses a mix of vaporized fuel and air in a cylinder through the rise of the piston stroke. Then ignites the mixture with a spark of electricity so that it burns explosively just before maximum compression. This can be done with either four stroke or two stroke engines. In order to run safely an Otto cycle engine must use a fuel that vaporizes easily, and it must not compress the fuel to the auto ignition temperature for that fuel. This compression limit is commonly described as the Octane rating. The higher the Octane rating the more the vaporized fuel air mixture can be compressed before it will auto ignite without the sparkplug igniting it at the correct time. Low octane gasoline has an Octane rating of 87 at most American gas stations while E-85 fuel has an Octane rating of 105. This makes E-85 fuel suitable for high compression Otto cycle engines with the correct fuel system components. Diesel cycle engines are internal combustion engines that compresses air with no fuel in it to a very high pressure which causes the temperature of the air to rise. This effect is known as Boyle’s Law, compressing a gas causes it to heat up and decompressing a gas causes it to cool down. Because the air has no fuel vapor mixed in it you can compress it to a very high pressure which causes it to grow very hot. In a Diesel cycle engine a fuel injector sprays a very fine mist of liquid fuel into the cylinder just as the gas reaches maximum heat and the heat causes the mist to burn very rapidly. The spray of mist is a very short spurt, but in that short time the burning fuel heats the air in the cylinder and keeps it very hot even as the cylinder volume expands as the piston goes back down. This steady high pressure lasts for most of the down stroke and provides great torque to the drive shaft. Much like Otto cycle engines a Diesel cycle engine can also be two stroke or four stroke with two stroke engines often given catchy names like ‘Power Stroke’ because every compression cycle leads to a power cycle. A four stroke cycle has a compression upward stroke, downward power stroke, upward exhaust stroke, downward intake stroke. By careful design a two stroke engine combines the bottom of the stroke into an exhaust/intake event by forcing fresh intake air into the top of the cylinder under pressure that forces exhaust gasses out the bottom of the cylinder through a side valve. You should also be aware that Otto cycle engines are not the only design intended to use easily vaporized fuels like gasoline or alcohol. The alternative gasoline design is the Wankel engine that uses lobed chambers instead of cylinders and pistons. This permits the engine to constantly turn through a cycle instead of forcing the pistons to reverse direction every half cycle.

### A closed system contains an ideal gas that expands to a fixed final volume. If the ideal gas can expand either at constant pressure or constant temperature, which of these two processes will produce the largest amount of work?

Most of the power is delivered along the high temperature isothermic expansion in the Carnot Engine. Most of the work is done on the engine during the isothermic compression See ,Four-stroke engine, for the Otto Cycle and ,Carnot cycle, for the Carnot Engine.

### Why do we use otto cycle for petrol engine?

Otto Cycle is an idealized cycle and is based upon some assumptions: Gas and air mixture are modeled as air and an ideal gas, which continuously circulates in a closed cycle. Thus, there are no intake and exhaust processes. All the processes making up the cycle are internally reversible. The combustion process is replaced by a heat-addition process from an external source. The exhaust process is replaced by a heat-rejection process and the gas returns to its initial state. petrol engines have an compression ratio of 6 to 10. The efficiency of Otto engine is function of compression ratio only. The higher the compression ratio the higher the efficiency of Otto Cycle. Where as Compression ratio is a function of fuel, engine design, and operating conditions. k= specific heat ratio The thermal efficiency curve is rather steep at low compression ratios but flattens out starting when r=6,,, increase in thermal efficiency with r is not that pronounced at high compression ratio. also when r increases temperature of fuel air mixture rises above self ignition temperature of fuel . When the mixture ignites without spark causing an early and rapid combustion of fuel ahead of flame front, followed by almost instantaneous burning of remaining mixture. This prominent ignition of fuel is called auto ignition and produces an audible noise called knocking. So to prevent that condition ,,,, we use Otto cycle for SI engines.

### What is otto cycle?

There are certain assumptions for air that we need to consider before studying the Otto cycle. It starts with the working fluid, which is air. It continuously circulates in a closed cycle. Air is considered as an ideal gas. All the processes in (ideal) power cycles are internally reversible. Combustion process is modeled by a heat-addition process from an external source. The exhaust process is modeled by a heat-rejection process that restores the working fluid (air) at its initial state. Finally, specific heats are assumed to be constant @25°C for air. We'll look at the Otto Cycle using Processes. Process 0: a mass of air is drawn into piston/cylinder arrangement at constant pressure. Process 1 is an adiabatic (isentropic) compression of the charge as the piston moves from bottom dead centre (BDC) to top dead centre (TDC). Process 2–3 is a constant-volume heat transfer to the working gas from an external source while the piston is at top dead centre. This process is intended to represent the ignition of the fuel-air mixture and the subsequent rapid burning. Process 3–4 is an adiabatic isentropic expansion also called the power stroke. Process 4–1 completes the cycle by a constant-volume process in which heat is rejected from the air while the piston is at bottom dead centre. In the final process Process 1–0 the mass of air is released to the atmosphere in a constant pressure process. . Hence, We first saw what the air cycle assumptions are and then saw what the otto cycle is?

### Why are the constant quantities during heat addition different in Otto and diesel cycle?

The Otto cycle idealizes the operation of a SI (spark ignition) engine where a spark at the end of compression ignites the fuel air mixture (mixed in the engine port or carburettor), which burns almost instantaneously, raising the temperature and pressure. This can be modeled as a constant volume heat addition. Whereas the diesel cycle idealizes the operation of a CI (compression ignition engine) where the air is compressed to a high pressure to cause ignition when fuel is injected into it in a fine spray, which causes a high pressure flame front that travels forward and burns the fuel while pushing the piston forward. This can be modeled as a constant pressure heat addition. In real engines, there are always losses and delays leading to thermodynamic inefficiency, and the P-V diagram does not exactly follow the "constant" lines. For more details, see these references: Engines: An Introduction: John L. Lumley: 9780521644891: Amazon.com: Books Internal Combustion Engines: Theory and Design; A Text Book on Gas-And Oil-Engines for Engineers and Students in Engineering (Classic Reprint): Robert L. Streeter: Amazon.com: Books Internal Combustion Engine Fundamentals: J. Heywood: 9781259002076: Amazon.com: Books

### Can you draw 4 and 2 strokes Otto and Diesel cycles (ideal and real cycles)?

Yes. Four Stroke: GAS POWER CYCLE Two Stroke: Overall: Difference between actual and theoretical Otto cycle Comparison between the three theoretical cycles

### What is the reason for distinguishing the working fluids associated with thermodynamics as pure substances and ideal fluids?

Ideal fluid, I think you mean ideal gas. Otherwise, it is not true. The reason is that there are two classification of thermodynamic cycles Gas-power cycle -which uses gas (or in thermodynamic analysis, ideal gas) as working fluid (Otto cycle, Diesel cycle, Brayton cycle, Ericson cycle etc.) Vapour-power cycle-which is based on phase change of fluid, and uses vapour as working fluid. (Rankine cycle, Refrigeration cycle etc.)

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