Hi Efficiency Engine Design

2/21/2002 | John Jamieson

[mamelukesabre]

Water injection is often used to lower cylinder head temps but does nothing to the burning of the gas.

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Exactly. It is actually wasting energy. The strategies for maximizing peak power output and for maximizing Miles per gallon, are not the same.

[mamelukesabre]

--if all the cyliders were common and inline, well, like they usually are of course, you wouldn't need that many solenoids, either, like one or two per bank if they were hefty enough. The other way like referenced the old caddy attempt, it was one per valve, with valves themselves always being a compromise because they are round. They add more, make them smaller, still a compromise for the area they want to cover. I think the whole dang head should open and close, skip the valves.

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I don't follow this at all. If the cylinders are all firing in unison, then you could use only one solenoid. But that would be really dumb to build a multi-cylinder engine where all cylinders fired together.

[Dinsdale]

Do you know if the current generation of F1 engines is 'short opening' the intake valve to produce results similar to what you are discussing (e.g. limiting the time open during the intake cycle, resulting in vacume at the bottom of the intake cycle but allowing a longer effective power stroke vs intake). I realize F1 engines are a special breed (19K redlines on 1.5 liter 800 HP V10 unblown motors), but fuel efficency is still a huge issue for them. They also don't publish any information, but they are all using computer controlled values so something has to have gotten out.

[mamelukesabre]

There's certainly something to be said for computerized engine management. There are, unforutnatley, thermodynamic limits - probably the most salient being that a Carnot cycle (which cannot be built) is the upper limit on engine efficiency.

I've always thought that more effort should be put into designing a good stratified charge system. It would allow higher compression ratios by increasing the "apparent" octane rating of this miserable quality gasoline we have to use these days.

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I think all that is needed is to simply remove all the "hot spots" from the combustion chamber....more attention to cooling uniformly and to material surfaces

[Dinsdale]

But that would be really dumb to build a multi-cylinder engine where all cylinders fired together.

The harley people would love it. Except their girlfriends would lube up the seat so bad they would slide right off.

[mamelukesabre]

The harley people would love it. Except their girlfriends would lube up the seat so bad they would slide right off.

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Whoa there. Let's not go bashing Harley's now. Harleys are actually a pretty good over-all design....better than most of the japanese bikes. A 1970 vintage harley with a 1200cc motor in a 600lb bike will get 50+MPG. A brand new 300lb rice rocket with a 600-900cc motor is lucky to get 30MPG. Granted, the harley motor isn't too glamorous in terms of technology, but it provides just the right kind of power/torque for the application and fits perfectly right between your knees.

[zog]

--no, they would allow follow some sort of normal firing pattern. Although making opposed cylinders that fire balanced like bmw motorcycle engines might be a *good* thing. Then they would need to be paired of course.

[nightdriver]

"I'm not sure I totally buy your theory about higher compression ratios being the reason for the higher efficiency."

It works out that compression ratio is the main parameter that determines efficiency. There are gains that can be realised by making sure ALL the induced fuel gets burned (more turbulance, residence time, etc.) but this only goes so far. In order to increase the efficiency of any thermodynamic cycle, heat has to be added AT THE HIGHEST TEMPERATURE of the cycle.

Any hydrocarbon fuel has about 20,000btu/lb, whether it's natural gas or crude oil, so that's all we have to work with. With higher compression ratio, higher combustion temperatures are accomplished and benefit efficiency right up to the metallurgical and mechanical limit of the engine.

So a diesel engine with it's 21:1 ratio (it wont even run with less than about a 16:1 ratio) will always be more efficient.

[techcor]

I think I can answer that one. They don't produce enough power (in the space and weight requirements). Also, because they are an external heat engine , they have been traditionally slow to start (have to warm up). If you're interested int Stirling engines, do a search on google for "Thermal accoustic engines". I call them genie bottles and they will be important to the future. Just not for transportation.

[blabs]

His name was Tom Ogle, and he created the ogle mobile. See some of the links I posted.

[Doctor Stochastic]

In burning fuel-air mixtures, more energy is converted into mechanical motion at higher pressures. The rest of the energy is discharged into the manifold or goes out the exhaust. Burning is more complete at higher pressures, less carbon monoxide and unburned hydrocarbons.

Higher pressures also produce more nitric oxides and thus are not allowed leading to:
more unburned hydrocarbons and carbon monoxide in the exhaust leading to:
a post drive train burner (catalytic convertor) needing:
more expensive gasoline without lead, sulphur, phosphorous leading to:
more crude oil per gallon of gas.

The additional discharge of heat into the manifold leads to heavier radiators needing heavier engines. I'm guessing that the cost of complying with the nitrogen oxide regulations costs about 35% in efficiency, not to mention that photo-reactive partially burned hydrocarbons are still increased.

[webstersII]

From my reading of this subject (which has been some years ago), the main issue of engine efficiency has more to do with the fact that you are only utilizing about 35% or so of the actual energy in the fuel. The remainder is heat loss due to friction and some other inefficiencies, but the majority of it is just lost through poor combustion (hence the reason for catalytic converters and other pollution control devices; perfect combustion would have zero pollutants).

The issue is that the fuel to air mixture is still not optimized at all times when the car is throttled at different levels. The ideal ratio of air to gasoline is 14 to 1 (by volume) for ideal combustion. To my understanding, the fuel injection systems of cars today still do not overcome this in any major way, and that is the main issue in poor efficiency of the overall system.

You can mix the fuel and air much more efficiently at a higher temperature but then the fuel mixture tends to become stratified and the result is severe detonation in the combustion chamber. Designing a way to overcome this detonation issue by heating the mixture but mixing it in a more uniform way may overcome this.

Popular Mechanics did an interesting series on this subject back in the early 80's. There were some guys who build race car engines who were experimenting around with trying to get the air-fuel ratio improved by heating and mixing the fuel.

I knew a guy who received his engineering degree at General Motors Institute. From my discussions with him, I decided that they didn't teach people to think outside the box at GM, they just wanted people to make small improvements and continue the basic designs that they have been working on for years. I would be surprised if they ever overcome this lack of efficiency in the basic internal combustion engine at any major American car manufacturer.

Solve the engine efficiency problem and you will absolutely change the whole world. And I firmly believe that someday someone will. Might as well be you!

Good hunting!!

[John Jamieson]

Yes, the "Miller cycle"

[VikingsRazeAVillage]

GOOD POINT about the piston rings.