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Differences Between Otto Engine and Diesel Engine Jin Zhihua 1023-25-9665 October 30, 2013 1 Introduction Otto engines and diesel engines are quite famous types of engines which are widely used especially in transports. Actually, otto engine is invented by Niko- laus Otto in 1860s,1 and diesel engine was invented by Rudolf Diesel in 1893. 2They are similar in some ways, so I will do a brief comparison in this report. 2 The Difference in Ignition In otto engines, air and fuel are taken into the cylinder together as mixture. The air-fuel mixture is carried into the carburetor, and it is ignited by sparks.In diesel engines, air is introduced into the cylinder through ducts combusted will suction valve while the fuel is introduced directly by means of an injector. The air-fuel mixture takes place in the cylinder. As it is also called compression-ignition engine, it is ignited through the process of compression naturally. Because of this intaking process, due to the speed difference of air and fuel, otto engine has a problem of distribution of air in each cylinders, which may lead to more emission of poisonous gas, and as diesel engine needs enough compression to ignite, more air is needed during intaking process. 3 The Otto Cycle and Diesel Cycle The otto cycle is mostly utilizing otto cycle, and the diesel engine, depending on the requirements, there are two kinds of cycle, including diesel cycle and sabathe cycle utilized, 3however, the two cycle for diesel cycle is quite similar, as the sabathe cycle only has one more isochoric process in the middle. So I will just do a simple comparison between the ideal cycles of otto cycle and diesel 1http://en.wikipedia.org/wiki/Nikolaus Otto 2http://en.wikipedia.org/wiki/Diesel engine 3http://en.wikipedia.org/wiki/File:Theoretical Sabathe process.gif 1 cycle. I also attached the graphic or the two cycle in the back to see it clearly. Otto cycle consists of mainly 4 steps: (intaking of air-fuel mixture) Isentropic compression, (ignition) Constant-volume heat-addition, Isentropic expansion, Constant-volume heat rejection(exhausting gas). On the other hand, the diesel cycle has 4 steps: (intaking of air) Isentropic compression(intaking of fuel), (ignition) Constant-pressure heat addition, Isentropic expansion, Constant-volume heat rejection (exhausting gas). So actually, considering the steps, otto cycle has constant-volume but no constant- pressure part and diesel cycle is the opposite. In this way, it is obvious that sabathe cycle, using both constant volume and pressure part, makeing an engine more effective in thermodynamical view. 4 4 Some Other Differences There are also some minor differences between otto enging and diesel engine, though most of these are because of the difference of the cycle utilized as men- tioned above, I will just simply discribe the differences I found in books and websites. 4.1 Compression Ratio and Efficiency The value of the compression ratio in spark ignition engines (Otto cycle) varies from 6-10, except in exceptional cases, while in compression ignition engines (cycle diesel) ranges between 14 and 22.5Relatively, the efficiency of otto engine is around 25%to 35% and the one of diesel engine is around 35%to 50%. 4.2 Exhausting Substance and Other Characteristics Otto engine emits plenty of CO2 and diesel emits less CO2 but more PM. Usually, diesel engine is more noisy than otto, but it does work as well as otto in low temperature.6 5 Conclusion So there are merits and demerits of each kind of engines, because of the com- bustion and main cycle. And personally, I suppose that that is why both of them are still being used, without being totally eliminated. 4Hajimetemanabukisoenjinkougaku, Nagayama Isao 5http://en.demotor.net/differences-between-otto-and-diesel-engine 6Hajimetemanabukisoenjinkougaku, Nagayama Isao 2