Quote:
Originally Posted by Diesel_Dave
You say that cold air has "more oxygen" and warm air has "less oxygen". That's sort of true. Cold air does have more oxygen per unit volume--but only because there's more air per unit volume. The temperature doesn't affect the percentage of oxygen in air--therefore the amount of oxygen per unit mass doesn't change.
Now, you might be tempeted to think that because the stoke of the engine is a fixed volume, that volume is what matters. However, closed loop control keeps the air-fuel ratio basically constant (near stoich)--and AFR is mass-based, not volume based--the throttle will adjust to keep the same mass of air regardless of temperature (by changing the intake pressure). So warmer temps mean higher intake pressures--to keep the density the same. Higher intake pressure means lower pumping losses and also lower throttle losses, therefore, better fuel efficiency.
Also, warmer air increases the flame speed, so the combusion happens more quickly, giving it more room to expand. That also increases fuel efficiency.
Diesels are a different story because they're typically not at constant AFR and also don't have flame propogation. I've gone into the details on how a CAI benefits a diesel in other threads, but since you asked about a gasser, I'll stop now.
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Thanks for that explanation. It is hard to find a legit explanation that doesn't just say it "works because it works".
So the question comes down to new technologies now.
With infinite cam profiles the cam profile is optimized to virtually eliminate pumping losses. Since it is 99% optimized the need for a wai is basically negated besides the slight minimal increase in flame speed (DI helps with this more). A cai though is still beneficial. Thoughts on this?
Side Note: For other readers, pumping losses are inefficiencies caused by vacuum created when the valve closes causing air to back track within the intake system. The engine has to work a little harder to draw back in this air which are pumping losses. Back in the day car tuners would run intake runners which were designed to eliminate this back pressure. Some new cars still use this idea but use an extra butterfly valve to simulate intake runners.