Has anyone tried removing the cold air induction duct to see if warmer air improves winter mpg? I'm thinking might speed warm up and fuel atomization.

 

It MAY help it to warm up faster, but anytime the engine is really running, the colder more dense air is best.

 

The colder more dense air is better for power.
The warmer more thin air is better for fuel economy.

Ken@Japan

 

We are NOT racing. This engine balances between MG1 and ICE trough the planetary gearset. My thinking is reducing the power potential will generate more electrical torque and use less fuel. Also this ICE has no heated intake manifold so really cold air could be a problem for atomization of fuel esp in the first 15-30 min of driving. However to warm air could cause the mass airflow meter to fail. I was looking at just removing the cold air snorkel and let the ICE draw from the engine compartment, looking for about 100 deg F on the intake temp on the SGII. Was wondering if anyone has tried this.

 

Could you explain that reasoning? We have a closed loop system with sensors for IAT, MAF, and A/F. Fuel atomization shouldn't be any different with a warm engine. If anything, I would think that the lower RPM with denser air would have an advantage for economy.

 

Its all about fuel atomization, thats why a cool engine gets HORRIBLE fe.

Air density is different depending on altitude and air temp. Pressure is corrected using a formula that includes altitude and temp for the specific location. So in Denver they may say the pressure is 29.67 but that is a corrected number. Higher presure, higher hp, lower pressure lower hp.

There is a useful formula that for every 10 deg F temp chang there is a coresponding 1% power change, Higher temp lower power, lower temp higher power.

We cannot change the pressure we drive in, but we can fake the engine into a "higher" altitude by warming the intake air, to bad it doesnt affect the areodynamic drag.

 

You're correct Prius ECU's always try to run the engine under stoichiometric(14.7:1) air-fuel ratio.
We know Prius accelerator pedal is just for power request input to the ECU's, drive-by-wire, then ECU's decide how much open the throttle.
Under the same level pf power request, the throttle is narrow open with cold intake-air and wide open with warm intake-air.
Therefore, there is less pumping loss when the throttle is wide open with warm intake-air.

Ken@Japan

 

Your argument makes more sense for an Otto-cycle engine. The efficiency improvement from pumping loss reduction has already been largely maximized in the Miller-cycle engine. Any marginal improvement would probably be negated by the increased RPM, unless of course the BSFC was less at the higher RPM.

If hot air was always better for FE, the intake air could easily be heated by the exhaust if the engineers so desired. That fact that it isn't speaks volumes.

 

Agreed, the poster makes a good point that is correct, but really only for regular Otto setups. The "Atkinson" (late-intake-valve-closing) type ICE mitigates a lot of pumping loss up front. Remaining potential pumping losses are further minimized by wide throttle openings. Contrary to what the poster says, the Prius throttle is rarely at what could be described as a "narrow open" condition.

The FEH uses the same trick. The throttle is typically farther open than one might expect, lessening pumping losses.

In a regular engine this would, of course, cause high RPMs. The engine would rev up when the throttle opens. This can be prevented by varying the valve timing as done on BMWs Vario Cam setup, which actually has no loss-inducing throttle at all and controls RPMs with the valves alone. In the case of the Toyota and Ford designs, the MG is used to prevent over-revving. The computer tells the MG to energize when the throttle opens. This loads and thus slows the ICE, preventing the revving that would normally result from WOT. Clever.

 

Which is exactly why modern vehicle all have a cold air intake. Economy. Colder=denser which translates to more power per engine revolution.

Warm air may result in leaner burning, but the corresponding combustion ineffeciencies and power loss just causes the engine to rev.