Percentage of non-ideal combustion is more in a diesel engine,why?

In summary, the difference in combustion between diesel and spark ignition engines is due to the fixed quantity of air and varying fuel injection in diesel engines, leading to non-ideal combustion at low power and ideal combustion at full power. This is in contrast to spark ignition engines, which require a stoichiometric air/fuel ratio to minimize air pollutants. The compression ratio remains constant in diesel engines, while only the mean effective pressure varies with load ranges.
  • #1
marellasunny
255
3
In this diagram,non-ideal combustion in a diesel engine takes-up a lot of the fuel energy. Why is this so? Also intrigues me that there is a lot more non-ideal combustion at low load than higher loads. Is this because the diesel engine operates with a lower compression ratio at lower loads? This leads me to my next question:

2.I've assumed the compression ratio to remain constant irrespective of the engine rpm,is that realistic?
LOGIC I USE: Only the mean effective pressure(measured at flywheel) varies with load ranges. The engine displacement remains the same.

http://imageshack.com/a/img571/7527/3l3n.gif
 
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  • #2
A spark ignition engine runs at a high temperature. To minimise the production of air pollutants such as NOx, a stoichiometric air/fuel ratio must be used in gasoline engines. There should be little unused oxygen available in the combustion products.

A diesel takes in a fixed quantity of air with each induction stroke and runs cooler than a SI engine. The full quantity of air must be compressed in order to reach a consistent compression temperature. Only sufficient fuel is then injected to generate the power required. Non-ideal combustion therefore occurs at low power, the unused oxygen flows out with the exhaust. At full power the maximum volume of fuel is being injected and almost all the oxygen is being consumed. That is the ideal stoichiometric situation as found in spark ignition engines. Any more fuel, or less air, and the diesel will produce black sooty smoke which is again, non-ideal combustion.
 
  • #3
Thanks
 

1. Why is the percentage of non-ideal combustion higher in a diesel engine compared to a gasoline engine?

The main reason for this is the difference in the combustion process between diesel and gasoline engines. In a gasoline engine, the fuel and air mixture is ignited by a spark plug, resulting in a more controlled and even combustion. However, in a diesel engine, the fuel is injected into the compressed air, causing it to ignite and burn unevenly. This results in a higher percentage of non-ideal combustion, as some fuel may not burn completely.

2. How does the percentage of non-ideal combustion affect the performance of a diesel engine?

A higher percentage of non-ideal combustion can lead to decreased engine performance, as it can result in incomplete burning of fuel and reduced power output. It can also lead to the formation of harmful emissions such as nitrogen oxides and particulate matter.

3. Can the percentage of non-ideal combustion be reduced in a diesel engine?

Yes, there are several methods that can be used to reduce the percentage of non-ideal combustion in a diesel engine. These include optimizing the fuel injection system, improving air intake and exhaust flow, and using additives in the fuel to improve combustion efficiency.

4. Are there any other factors that contribute to the high percentage of non-ideal combustion in diesel engines?

Aside from the combustion process, other factors that can affect the percentage of non-ideal combustion in diesel engines include the quality of fuel, engine design and condition, and operating conditions such as load and speed.

5. How important is it to minimize the percentage of non-ideal combustion in diesel engines?

Minimizing the percentage of non-ideal combustion is crucial for both engine performance and environmental impact. Inefficient combustion can lead to decreased fuel efficiency, increased emissions, and potential damage to engine components. It is important for manufacturers and users of diesel engines to continually improve and optimize combustion processes to reduce the negative effects of non-ideal combustion.

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