12-06-2015, 07:25 PM
Really interesting stuff!
Monitoring your air inlet temperatures is key to making decent power with any engine! But there's a bit of confusion between SI (spark ignition) engines with CI (compression ignition) engines - their limiting factors are quite different!
Petrol motors "knock" because their fuel (generally...) is mixed with the air as it enters the cylinder via the injector in the inlet manifold, this means that the fuel gets heated significantly by the compression of the engine and certainly the inlet temperatures!
Diesels can't "knock" or "pre-ignite" - by the fact they're Direct Injection - there is no fuel mixed with the air before top dead centre, therefore it can't accidentally ignite it. The diesel will ignite shortly after you inject it - in the HDi engine, this is calibrated inside the ECU, it's calculated by factoring in mainly the amount to be injected and the engine speed, but also all sorts of other variables like air temperature and coolant temperature to ensure that it's correct for the operating condition of the engine.
However Diesels are limited by their ignition delay, which inlet, cylinder and fuel temperature do affect - it's by no means a simple factor!
If anyone is interested in Diesels and stuff about injection timing, which is also closely related to inlet temperatures - here's a cracking article about it:
http://killerbeeperformance.com/download...Diesel.pdf
Monitoring your air inlet temperatures is key to making decent power with any engine! But there's a bit of confusion between SI (spark ignition) engines with CI (compression ignition) engines - their limiting factors are quite different!
Quote:The article does not specify why the injection cycle is extended, however going off my own knowledge I would say that perhaps its done to aid in the cooling of the air temps and reduce the chance of knock from the increased temperature of the mix during the compression cycle which could cause the mixture to ignite before optimal angle.
Petrol motors "knock" because their fuel (generally...) is mixed with the air as it enters the cylinder via the injector in the inlet manifold, this means that the fuel gets heated significantly by the compression of the engine and certainly the inlet temperatures!
Diesels can't "knock" or "pre-ignite" - by the fact they're Direct Injection - there is no fuel mixed with the air before top dead centre, therefore it can't accidentally ignite it. The diesel will ignite shortly after you inject it - in the HDi engine, this is calibrated inside the ECU, it's calculated by factoring in mainly the amount to be injected and the engine speed, but also all sorts of other variables like air temperature and coolant temperature to ensure that it's correct for the operating condition of the engine.
However Diesels are limited by their ignition delay, which inlet, cylinder and fuel temperature do affect - it's by no means a simple factor!
If anyone is interested in Diesels and stuff about injection timing, which is also closely related to inlet temperatures - here's a cracking article about it:
http://killerbeeperformance.com/download...Diesel.pdf
