i was reading the other day about air fuel ratio in wikipedia ( i guess it cannot be trusted) but can a car have an air fuel ratio of 45:1 or higher????
also has it ever been tried out practically????
A diesel engine can operate happily with an A/F ratio of 45:1. But a spark-ignited engine (like in F1) wants something very close to stoichiometric (approx. 14.7:1) for best power. An very lean A/F ratio of 45:1 in an SI gasoline engine would result in severe detonation and unstable combustion.
A word of advice: Wikipedia still promotes the widely discredited myths about AGW, so you should probably find yourself a better technical reference than Wikipedia.
Regards,
riff_raff
"Q: How do you make a small fortune in racing?
A: Start with a large one!"
i know that it will be an extremly lean mixture but at the same time... will it be possible to obtain the required power to run the engine considering the factor of octane no of the fuel???
( if the fuel being used consists of high concentration of chemicals.... then naturally more air will be required to dilute it and thus the ratio increases)....
Petrol racing engines (in fact all high revving engines, and even some not-so-high-revving road car engines) run on rich AFR (lambda at & below 0.8 in some cases) for many reasons. AFR is hardly a constant - it depends on engine load, revs, etc. You can see some old BMW turbo engine dyno-run here. Perhaps anyone can enlighten us with specific numbers for modern F1 engine?
Ratios below 0.8 are not seen on modern racing engines, that is very rich.
The reason you will typically see the ratio decreasing with higher speeds typically for a turbo is because the charge temperature also increases. One way to stop detonation at elevated charge temperatures is to overfuel to cool the temperature.
This is one of many problems that downsized, highly turbocharged economical engines of the future will have to deal with: there is no use in downsizing the engine for economy then have to inject more fuel to deal with the high inlet temperatures because of the high boost pressures.
I believe that using ethanol as a fuel could be a very effective way of overcoming this issue. Not sure if any manufacturer is looking at this method, have been out the engine development loop for a couple of years and developments come thick and fast.
I am not going to post much on this topic as I don't have time now but it's definetely interesting.
regarding numbers of a modern f1 engine... the air-fuel mixture is in the ratio of 12.5:1 or 13:1....
my question is if the compression ratio of the engine is increased can a leaner air fuel mixture be used to obtain the power which is produced currently???
regarding numbers of a modern f1 engine... the air-fuel mixture is in the ratio of 12.5:1 or 13:1....
my question is if the compression ratio of the engine is increased can a leaner air fuel mixture be used to obtain the power which is produced currently???
Not with petrol unless different types and percentages of additives are used, petrol would detonate without the right mixtures.
Of course it is conveniently forgotten that both ethanol and methanol need no additives for use at much higher compression ratios i.e 17 to 1.
LPG gas is also far better than petrol. I was involved once with a touring car designed to run on LPG and it easily beat the petrol cars until banned by pressure from the oil companies.
Direct injection or not, you're still at the mercy of the fuel. 91 octane gasoline is going to pre-ignite at a given cylinder temp regardless of injection method. Direct injection can help fuel economy by applying the fuel in a better burning pattern (and require less fuel to complete a good burn) but if the CR goes up you still need better fuel to deal with the increased cylinder pressures and temps.
I see what poster Rooky is getting at.
The thing to remember, Rooky, is that unless the air/fuel ratio is prety close to correct, it won't burn/ignite. Sure, it can be a little lean or a little rich but will then require a particularly strong ignition and good combustion chamber design. Of course the power output of the engine will be reduced, also the driveability. Also, with a lean mixture, it takes longer to burn which means it is still burning when the exhaust valve opens, this leads to grosely overheated ex valves and seats and early failure, not to mention overheating of the engine itself.
If you're interested in economy, bear in mind that slightly lean is good, but too lean (and still drivable), apart from causing valve problems and possibly piston problems due to heat and detonation, you'll probably end up using more petrol simpily because, due to reduced power output, you have to use higher throttle openings to avhieve the same results!
Regards
PK.
Besides the high-voltage, high-pressure DI systems that reduce this side affect somewhat (and have their own packaging disadvantages due to the additional required systems), didn't high-revving DI engines still have problems with the proper amount of fuel atomization? As far as I know this reduced atomization (hence reduced mixture-quality) is one of the reasons why recent production superbikes tend to use fuel injectors higher up in the intake trajectory when operating above a certain rpm range...
