WhiteBlue wrote:alelanza wrote:WhiteBlue wrote:The ignition is actually some degree after TDC and the 12-15° ignition after injection is required to evaporate the fuel and help it cool the compressed air.
I think you have the bolded words all mixed up
Injection starts 20° before TDC
Injection ends 10° before TDC
Ignition happens appr. between 2-5° after TDC
-> ignition 12-15° after end of injection to allow for proper evaporation and ignition in the downstroke.
xpensive wrote:Never mind ignition WB, do you have any more info on that gorgeous Ferrari I4?
WhiteBlue wrote:The "late" ignition is to make sure that you have sufficient evaporation due to the comparatively late injection. That is what they have found gives you the most efficient combustion. No, there is only one ingnition normally. Of course one can also go to laser based linear ignition, which is better but more expensive.
The reason why this is more efficient is the maximum use of the the fuel evaporation enthalpy for suppression of knocking. It means you can go leaner even at full power. At port ignition the evaporation happens in the ports and the cooling energy gets lost for the compressed charge. There is also fuel lost which remains on the walls of the intake system. As I have said before the direct spray guided injection gives a massive step in fuel reduction compared to port injection. At part loads it can be up to 20% and at full load I still reckon 5-10% .
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