Quote:
Originally Posted by ChazInMT
Funny, back in November I got into a thread discussion where a guy who was claiming that Variable Valve Timing was a way to eliminate pumping loss, I thought he was full of it, but this led me to research the whole VVT thing and really cemented for me how it is that intake systems control the power of engines. The thread is Warm Air Intake (WAI) vs Cold Air Intake (CAI) ... School Me and worth having a look at.
Modern engines are 98%+ efficient at burning all the fuel that goes into the cylinder, so looking to improve fuel efficiency by claiming to promote “Better Combustion” is ridiculous. Pumping losses are a result of the cylinders in our engines needing to pull a small amount air into the cylinder in relation to what the cylinder is capable of pulling in. These result in about 3% of the energy produced by the engine being wasted on this process. No modification of the throttle body can eliminate this loss. |
Well removing the throttle plate would,
, but then you'd be at constant WOT. Actually I've heard Formula 1 cars didn't have throttles for a while until they mandated them, they controlled engine speed and output purely through valve and ignition timing, though Formula 1 cars tend to be driven at WOT most of the time, unlike regular cars. Isn't the pumping loss a necessary evil of the Otto cycle? The throttle controls engine speed and power output by inducing a vacuum, thereby reducing fuel/air mixture? Doesn't variable valve timing do the same in effect? Or does VVT produce a mild simulated Atkinson cycle? Actually reading about how the Yaris and Prius engines are basically identical except for the pistons and camshafts made me wonder about an engine that used VVT to switch between Otto cycle for high load and simulated Atkinson cycle for low load. Only problem would be compression, if you used a high compression ratio, like the Prius, to make up for the volume lost during the compression stroke, the Prius has a possible compression ratio of 13 to 1 but because of the Atkinson cycle, its effective ratio is something like 10.5 to 1. This would necessitate the use of high octane fuel to prevent knock when in Otto cycle. Or the compression could be left at a normal ratio, but then the ratio during Atkinson cycle would be quite low, reducing efficiency but allowing the use of low octane fuel. Sorry, I've been mulling this over in my head for a while.