Pumping loss reduction strategies

[Bicycle Bob]

Aye, it is far better to close the intake early than late. Late closing pumps the mixture twice to no purpose at all. The best retrofit, and a candidate for OEM is a reverse supercharger - run the generator off the intake vacuum. That makes it easy to have a regular supercharger, but then it becomes very helpful to get a variable compression ratio to keep the actual charge density at ignition uniform. Perhaps the main bearings should sit on a series of ramps that can be cranked fore and aft.
Ideally, the exhaust valves should not release unused pressure, but we currently waste the intake pressure differential needed for that without a true Atkinson crankcase.
Lean burn is wonderful for efficiency - those NOX producing temperatures mean high Carnot efficiency. A stratified charge and some EGR help to tame it, but catalysts probably leave more efficiency.

[cRiPpLe_rOoStEr]

Originally Posted by Bicycle Bob

Ideally, the exhaust valves should not release unused pressure, but we currently waste the intake pressure differential needed for that without a true Atkinson crankcase.

The only advantage that I can see in that Atkinson effect applied through a longer intake valve timing is that the mixture that goes back to the intake manifold decreases further the temperature of the subsequent intake charge.

[Bicycle Bob]

That re-pumped mixture will be hotter both from friction and from cylinder heat.

[LittleBlackDuck]

Originally Posted by cRiPpLe_rOoStEr

The only advantage that I can see in that Atkinson effect applied through a longer intake valve timing is that the mixture that goes back to the intake manifold decreases further the temperature of the subsequent intake charge.

If the charge has entered the cylinder and has also been squeezed somewhat, then Boyle's law and common sense would expect the charge temperature to be higher, even allowing for the latent heat of evaporation of the fuel.

Simon

[cRiPpLe_rOoStEr]

Maybe I got it the wrong way, but I've seen some claims that it keeps the intake charge colder and that it was the reason why Toyota retained a regular port-injection instead of upgrading to direct injection in the current generation of the Prius.

[LittleBlackDuck]

Originally Posted by cRiPpLe_rOoStEr

Maybe I got it the wrong way, but I've seen some claims that it keeps the intake charge colder and that it was the reason why Toyota retained a regular port-injection instead of upgrading to direct injection in the current generation of the Prius.

Port injection vs direct lowers the intake temperature somewhat. This is offset a bit by the heated charge being pumped back into the intake from the cylinder.

I am interested to see where Toyota goes in future updates of this series of engines.

Simon

[serialk11r]

Originally Posted by ChazInMT

Annnnd you totally dissed BMW's Valvetronic and some others Variable Valve Lift (VVL) systems which change the displacement of the engine by varying the intake valve to close before BDC on the suck stroke. In fact they keep the throttle plate wide open on those engines using the valves to "Throttle" the engine. It'd be somewhat difficult to retrofit your Geo Metro engines with it. Just sayin. Although I bet that magnificent b@st@rd MPGeo could pull it off....that guys a frickin genius.

Actually I think these are good case studies for understanding why a lot of manufacturers have not gone down this road. Every BMW today is equipped with Valvetronic, and thus has miniscule pumping losses, yet the fuel efficiency is not really stellar. My parents leased a new BMW hybrid X5 and its gas mileage really isn't much better than an MDX or RX350. It's better, but not by much.

Are BMW sedans much more efficient than Mercedes sedans? Nope.

Same with the Fiat Multiair, is the Fiat 500 getting far better gas mileage than a Smart or Scion iA? Don't think so.

Do the Nissan VQ37 cars get better gas mileage than Toyota 2GR or Honda J35 cars? Not really.

Pumping losses are only part of the equation. Mechanical friction is still the biggest culprit, which is why transmissions are getting more and more gears since that is the cheapest way to improve efficiency. It's worth remembering that pumping losses can only be a bit over 100kPa in specific torque, but friction can be several times that, and as you get into very low specific output ranges the combustion temperature is so low that the gas cycle efficiency itself is total crap.

For most cars, regearing them taller (with tires is cheapest) and running them a little leaner gets you most of the way for cheap. Tuning the engine lean can raise your manifold pressure by 10-15%, which translates into 1psi reduction in vacuum on the freeway for most cars. A reasonable cam will reduce the vacuum by maybe another 1psi. In some cases like my FR-S, there's some money left on the table with the VVT, and you can get another 0.5-1psi or so, and that's already half your throttling losses.

This is why Toyota has mostly ditched their variable lift approach and gone with very wide angle cam phasers in their newest engines.

[LittleBlackDuck]

Originally Posted by serialk11r

(Snip)
This is why Toyota has mostly ditched their variable lift approach and gone with very wide angle cam phasers in their newest engines.

Less complication and Atkinson on demand. Next step is the camless engine that will give full control of valve events.

Simon

[Ecky]

Originally Posted by LittleBlackDuck

Less complication and Atkinson on demand. Next step is the camless engine that will give full control of valve events.

Simon

I'm willing to bet we'll be mostly electric before that happens.

[LittleBlackDuck]

Originally Posted by Ecky

I'm willing to bet we'll be mostly electric before that happens.

Would be good, if range anxiety does not intervene.

Simon