trinidefender wrote:gruntguru wrote:Of course the ICE in both cases is a diesel which means the AFR can be chosen to maximise efficiency since detonation and flame propagation are unaffected by mixture. What it does tell us however is that somewhere around 1.5 is the place to aim for best efficiency provided detonation and flame propagation can be effectively controlled (by optimising DI etc).
While I do personally believe that current F1 engines run slightly lean of lambda (~1.2), there are a few problems with your post. Firstly it is a diesel piston engine. Diesels never run close to stoichiometric in piston engines because it is very hard to achieve complete combustion with compression ignition.
That doesn't contradict the reasoning in the above paragraph I have requoted. The primary motivation for not running the Nomad and the Garrett model even leaner would be the reduction in power/weight ratio.
Combustion stability and ability of achieving complete combustion improvements in recent developments of diesel engines is the reason why modern diesels are getting closer to stoichiometric and making more power.
"more power" per unit displacement but not
"more power" for a given fuel flow so not
"more power" in the fuel-restricted F1 sense.
OTOH a higher pressure ratio in the turbomachinery is clearly a benefit to TE so I suspect the mixture chosen will be the leanest value that allows efficient heat release.
The napier nomad also used a system that used excess air and burned it in a separate combustion chamber before flowing through a turbine that powered the compressor and crankshaft.
Of course that would murder the efficiency and would only be used for emergency or take-off power.