Direct injection spark ignition with gasoline engine

  • Thread starter sid_galt
  • Start date
  • #1
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Main Question or Discussion Point

If someday complete direct injection spark ignition with gasoline engine with Otto cycle is achieved so that very high pressure ratios are possible, what would be the impact on the automotive industry?
 

Answers and Replies

  • #2
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You can do that now, and you'd have a Diesel Cycle engine. That is the constraint that defines Diesel. The spark would simply be a redundancy.

KM
 
  • #3
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But the diesel cycle engine runs on the brayton cycle. I am talking about the Otto cycle which is more efficient since the pressure rises while combustion and further energy can be extracted from the exhaust if it is not fully expanded to atmospheric pressure.
 
  • #4
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sid_galt said:
But the diesel cycle engine runs on the brayton cycle. I am talking about the Otto cycle which is more efficient since the pressure rises while combustion and further energy can be extracted from the exhaust if it is not fully expanded to atmospheric pressure.
The Diesel engine runs on the Diesel Cycle. All you have to do is compare the P-V curves of the Otto and Diesel Cycles, and you will see the link. If you extend the 'compression' curve of the Otto cycle past the usual 'ignition point', you'll get exactly the curve of the Diesel Cycle. (Not quite that simple, to be sure.)

Both the Otto and the Diesel Cycles have the common characteristic of accomplishing the Intake, the Compression, the Combustion, the Expansion and the Exhaust in the Same place (Cylinder Chamber?). The Brayton Cycle (Which I personally prefer) Moves the air from place to place to accomplish these stages. To go from Otto to Diesel Cycle (as your suggestion does) only requires that fuel 'injection' be held off until you are ready for combustion, thus avoiding premature ignition (called Dieseling). The reason for spark plugs in an Otto Cycle, is just to get control over when combustion occurs, rather than having pre-ignition (Dieseling). The other way to control when combustion occurs, is to hold off fuel injection; exactly what a Diesel does, and this allows greater compression ratios. You described conversion from Otto to Diesel Cycle.

KM
 
Last edited:
  • #5
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Thanks for the help
 

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