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The future of the engine as we know it 1

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franzh

franzh

Automotive
Jun 4, 2001
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I normally run like crazy when someone asks me questions about a "new" engine, but when one of my directors asks me to evaluate a "new design" design, my knees shake. That happened this morning.

We have seen free pistons, opposed oscillating pistons, scotch yoke pistons, toroidal blocks, ball valves, sliding sleeves, and tons of other combinations. Strangely, or not so strangely, none of these has ever reached any significant success. The old, inefficient Otto cycle engine still hangs around. With the exception of sealing refinements and air-fuel metering, almost nothing has changed in 100+ years, not including OHC engines which is a refinement, or phased cams, also a refinement, or exhaust aftertreatments, which is not a refinement, but an attempt at fixing an engine inefficiency.

I wonder how long it will take before something else pops up and takes a reasonably strong stand against the tried and true engine design?

Lets look at the true IC engine replacement, not hybrids (although I feel that is where we are heading for the next 25 years). Turbines are nice but not practical for a number of reasons.

When we look at H2 as a potential fuel, it still uses the Otto cycle engine as a base, only the fuel has changed. Are we really gaining anything on the engineering side? I recognize the significant advantage on emissions, but fuel transport, storage, and infrastructure have still to be perfected.

Any ideas, fellow engineers?
Franz


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Terry -

Congratulations on the patent! That's exciting news. What about just hauling your test engine to their location? No substitute for the real thing to generate interest. Or to a manufacturer?

globi5 -
Very interesting article. I haven't had time to look through it completely, but they clearly grasp the basic challenges facing IC engine efficiency, and they seem to have a realistic plan to address them. Is there more information available?
 
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The whole project of the car with the high power density engine was funded by greenpeace (they wanted to show that it is possible to build a relatively inexpensive 80 mpg car without diesel, hybrid, fuel cell or solar technology.)
(It's actually not a hybrid as this article falsely claims.)
Also, the original Smart ( owned by the Swatch-group was supposed to be fitted with a similar engine before it was sold to DaimlerChrysler which decided to provide it with their own 600cc turbocharged 3 cylinder instead.

Here's more info about the pressure wave supercharger (it was originally invented by BBC (now ABB) about 50 years ago):
As with the Miller cycle engine Mazda was the only company that actually lead it into production (well as far as I know). I don't know why Mazda stopped producing them? Maybe because turbochargers were massproduced and readily available and it was therefore not cost effective?
 
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globi5 --

I'm with you on the idea of making the engine efficient at low throttle settings. That is the crux of the issue, because you are right, 90% of most driving cycles is done at partial throttle.

In automobiles, engines are in general hugely oversized to get acceleration, leading to greater engine friction due to larger engine size, and, much more importantly, to running at poor sfc due to low BMEP (I believe this is the correct way to express it). I have not yet seen any IC engine that can run at optimal or near-optimal sfc over the full range of engine loads and speeds -- not even close. Otto engines are simply not designed for it - particularly gasoline, spark-ignited, throttled engines running at stoich. The primary thrust of hybrids is, if you will, to try to mitigate this problem by stressing a smaller engine harder and getting power boost for the 10% of the time when it is required by using batteries, flywheels, ultracapacitors, etc.

The best answers I've seen to this problem are similar to those expressed in this link you provided:
namely, run higher BMEP, run lean, do EGR (perhaps), use VVT to try to approximate variable stroke and/or a Miller cycle, and run smaller and faster at higher boost pressure.

Yup. All of those. Add HCCI to run at detonation and thus close to ideal constant volume combustion (not to mention reducing heat loss and running at CRs approaching 50:1, at AFRs up to 40:1 or more), allow for real variable stroke in its purest form, use GDI partly to concentrate a richer area of charge but mostly to avoid blowing fuel out the exhaust in a two-cycle configuration, get rid of cranks to get real savings in engine friction, and run at really outrageous speeds while firing at every stroke to really get engine size down (I'm shooting for around 100 hp and 250 lb-ft. of torque, at least, at 0 rpm, from a 200cc engine).

Franzh--
Does that qualify as taking a "reasonably strong stand against the tried and true engine design?"

Sorry I'm not an engineer (so I'm told), but rather than waiting for something to "pop up," I've decided to try my hand at designing and building an engine anyway. Who knows? It might even work.
 
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schwee--

Do you happen to have a website showing your engine?

I agree with what you said, but with low AFRs, I'm not quite sure whether this a really such a efficiency increasing measure, just because you obviously end up pumping a lot of air for 'nothing' and therefore increase your pumping losses.
I can only see the merits if it's the only possibility to realize a constant volume combustion.

I think another alternative could be if you had a miller cycle engine with an electric supercharger. Instead of using the recycled braking energy to propel the car, you could use it to supercharge the engine.
Why? It's less efficient but you can save weight because by using the electric energy to supercharge the engine you'd end up with about 4 times more power than you'd end up by using the electric motor to power the car directly. Also you could use a centrifugal supercharger which is inherently lighter and adiabatically more efficient than a roots supercharger. Since you can control the speed of the supercharger independent from the speed of the engine this concept would give you more control over the supercharger as well.
 
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globi5-
Well, sort of..
You can try Look under Projects, Project X.

That gives a general overview. The free-piston compressor/combustor (X combustor, is I think what my partner calls it) is the innovation.

You have a good point on the possibly diminishing retuns of ultra-lean mixtures. I'm basing my estimate of its value on some experimental observations of a very similar engine (double-acting HCCI free-piston linear alternator) that has been built at Sandia by Van Blarigan and Aichlmayr. There's a good paper on it that's hard to find, but this is the gist:


Hmmm-- the Sandia guys use an electric supercharger, (turbocharger?) too. That's a good thought. I'm not wild abut regenerative braking, though, partly because I think I've heard estimates of about 5% of a combined (or even city?) driving cycle being braking, plus the added weight and cost of batteries and motors, and what I think may be problems with rapid charging of batteries (though it seems I may be mistaken there.) But using a much smaller motor to supercharge the main engine to get more bang for the buck is a very good plan. My issue is with supercharging/turbocharging in general as an efficiency measure-- since you have to downgrade the normally aspirated CR to accomodate the forced induction, you're left with poorer efficiency when you're non-turboed. Ah - supercharging obviates that.

So I still haven't had time to plow through your links, but what is the gist of what the Wenko SAVE guys are up to? I see references to a "pressure wave supercharger" and "variable gas pocket intake" but no tables or diagrams seem available on that link. I don't quite understand how they propose to do spark-ignition lean burn, unless they use GDI (?) or swirling or something to richen the mixture near the spark plug (I think Mitsubishi is trying this). I also don't see how they're going to avoid deterioration of BMEP in a throttled engine at partial load. Maybe that's what the pressure wave supercharging is about.

What's your idea with the Miller cycle? Are you going to do it with valving?
 
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On this of Franz:
>>>>Is the answer recovering the waste heat and totally transforming the thermodynamic capabilities of the fuel to usable energy?

What about cutting down on the waste heat in the first place? Who said that is a given? My take is that waste heat comes from combustion gases at high temperature sitting around "too" long in the cylinder, heating up cylinder walls, etc. Have 'em do their thing and get 'em out of there. Also, there are inherent problems of not recovering compression energy due to expansion stroke not being longer than compression stroke, etc., and blowing heat out the exhaust. So try to approximate a Miller cycle.

Obviously, you're right that no engine is 100% efficient. But what about 50%? 60%?

One question that has puzzled me is whether we are measuring the thermodynamic efficiency of a gasoline engine (say, 20%-25%) at optimal sfc or at partial throttle. I suspect that 25% represents optimal, and it deteriorates from there. So if you can bring up the part-throttle efficiency (I don't know, 10%?) to match the optimal sfc, you've gained a lot already.
 
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schwee--

Thanks for the links. I'll read through it. (And 100HP for a kart is plenty. Btw talking about karts: What I find interesting is that there's still no maintenance free (or little maintenance) race kart package out there.)

Regarding the electric supercharger:
Because you use the electric motor to supercharge the engine you can get away with less weight. Yes you still have to charge the batteries or capacitors very rapidly and braking energy might not be sufficient to charge the batteries (especially if you don't do a lot of city driving) but you can also charge the batteries at partial load.
I'd use the miller cycle because you don't need to downgrade the CR. The miller cycle reduces the volumetric efficiency but allows the CR of the engine to be kept the same. The supercharger makes up for that loss. Example: The Prius (miller or atkinson cycle) has a CR of 13.5 and reaches an efficiency of 34% with a gasoline engine.

Regarding Wenko:
The Wenko guys are using a very small engine (360cc) to produce the power necessary. This way they can reduce the frictional losses and the weight of the engine. To generate the extra power they use a pressure wave supercharger, which compared to a turbo doesn't have a lag and is probably even more efficient. Actually Ferrari was testing it in a F1 engine about 20 something years ago.
There's no lean burn. It is simply a very small engine that can produce a lot of power only if necessary.

Pressure wave or comprex supercharger or wave rotor:
The pressure wave supercharger does basically the same as a turbocharger just without a turbine and a compressor wheel. To put it very simply: The exhaust gas compresses the intake gas directly.
 
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By nature and design, almost all gasoline spark ignited engines are throttled. One of the biggest culprits for engine inefficiency are suction throttling losses. Visualize pulling three (for a 6 cylinder engine) 3" diameter suction cups 3", 1200 times a minute, or 20 times a second. That is roughly what an engine has to overcome at part throttle and 1200 rpm, or a slow speed or fast idle. I agree that most of today’s engines operate at part throttle and that is certainly not the most efficient mode of an engines operation.

The idea of getting it out of there quickly bears some merit and is one of the reasons for variable cam timing. What cam lobe profile and timing event works for idle is not exactly ideal for part throttle or full load.

As for the other posters, this thread is to discuss what engines may be like in the future. I appreciate discussing new ideas and rehashing old ones, but be careful of posting self promoting designs. As a patent holder myself, owning a patent simply means no one has done it before you, not necessarily that it works. As a reference ONLY, no specific inference intended or implied, there are almost 300 patents on file of overunity engines, or engines that make more power than is inputted, also called the Perpetual Motion machine.

Franz

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
 
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Franz, good job clearing the air with reality here. And the rest of yous guyz, the next significant breakthrough for SI is to minimize ring crevice outgassing and pumping loss. Throttling via plate or valve actuation is not required, they are crutches to facilitate antiquated dare I say cheap to facilitate combustion strategies. The real interest in plasma ignition is its capacity to produce enough btu's of heat to ignite... um, we can call it dieseline for now. Lean direct injected gasoline mixtures, guided away from heat robbing flame quenching ring grooves and walls, on the order of 80:1 facilitate low load decel due to the inadequate heat to tick the engine over but enough to keep a nox reduction cat lit using combustion heat. Part of the strategy involves throttling up to 50% egr in order to reduce excess heat loss. Various aspects of this work have been in the lab at a few universities and at numerous oem consulting and component supplier locations for some time. Thermal efficiencies in the peak neighborhood of 28% are the norm for SI, 39% for unthrottled is the best I have witnessed. Others report up to 45%.. I dont beleive 45%. Best case diesel is not that good in production. The real advantage of all this is particulate free with closer to diesel efficiency without currently unmanageable CI cold start emissions.

In the future the SI and CI engines will have more in common and dieseline may become the norm. This is not new news. Why don't we have it yet? The technology has to be more reliable and less costly than the reliable status quo AND without unacceptable risk.

To get there gasoline must be accomodated because a $900billion intl fuel station infrastructure is in place.
 
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I still think downsizing and supercharging appears to make more sense than leaning the air fuel mixture. If you run an engine with small displacement at a given rpm and 16:1 AFR, an engine with double displacement needs to run at 32:1 AFR in order to consume the same amount of fuel. However the large engine has higher frictional losses, has to pump double the amount of air (or recycled exhaust gas), the combustion chamber has more surface (more heatloss) and the engine has more mass (more drag, reduced acceleration, mass distribution etc.). The only advantage of a larger naturally aspirated engine as opposed to a smaller supercharged engine is it's possibly cheaper to manufacture and maybe more reliable - or what is it? (If it's a miller cycle it doesn't need to have a lower CR.)

Another advantage of supercharging is that it can exploit the higher knock resistance of ethanol by simply increasing boost. (If someone wanted to switch between gasoline and ethanol).
Also an engine with a pressure wave supercharger has EGR basically integrated (no extra piping and valving necessary).

I wonder whether we'll ever see laser plugs in engines of passenger vehicles?
Of course a very simple way to reduce pumping and frictional losses would be by having an extra economy gear (which seemed to have disappeared as well - my car runs 70mph at 3000rpm in 5th gear and I'm sure it could do the same at 1500rpm).

schwee-- Doesn't a gasturbine usually have difficulties to react to rapid load changes? Or are there ways to solve this?
 
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globi5:
I think that you will find that the Comprex Pressure-Wave Supercharger is now owned by Caterpillar. I believe that they purchased the rights to the concept about 8 or 10 years ago, perhaps recognizing that the future would require EGR and high boost levels. It turns out that while the Comprex will give you boost with some control over EGR, it is not capable of the pressure ratios that modern engines and certainly future premixed diesel engines require, and which can be had from (1 or 2-stage) turbochargers.

While the previous incarnations of the Comprex concept had the rotor belt driven at a fixed ratio from the crankshaft, the ultimate intent was to have the rotor drum driven by a variable speed motor, so that the system could be tuned for torque demand, gas temperature, and other variables.

PJGD
 
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globi5-
Sure, gas turbines are terrible in regard to rapid load changes. They also simply eat fuel at idle. Gas turbines are totally inappropriate for automotive use, as Chrysler found out in the 1960s. They have their limitations in other applications as well, which are not limited to their being expensive.

However, I'm not proposing a gas turbine. Maybe the easiest way to conceive of what I'm on about is to take a look at http: and go to


and download the free "alternaTIFF" viewer.

Then go to the home page, left column, Patent, search, then
Patent Number Search, and search on

1,785,643 (include the commas).

Click on "Images." You can't access the thing without downloading the Tiff viewer, or at least I couldn't.

Anyway, you'll find a 1930 patent for a rather ingenious system for using a linear alternator/motor to rotary alternator/motor system designed to smooth the oscillations in a double-acting compound free piston-gas turbine engine (whether it is HCCI or not is not specified -- it certainly could be).

Forget the smoothing system, which is actually what the patent is for. Focus on the engine. That's what I'm talking about (more or less). Check it out.
 
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PJGD:
Do you have more information on plasma ignition? I don't fully understand its purpose, but it could be useful to me to know.

Of even more immediate relevance is lean direct-inject gasoline, which is exactly what I propose doing, I think. That is, what I really need is any information about developments in direct in-cylinder injection of homogeneous mixtures in a gasoline engine, at not especially high pressures but very fast (20,000 rpm equiv). Mixture range needs to be lambda 3 (say) to stoich. The reason I want this is so that I can inject fuel after my piston has already closed off my exhaust ports in my two-stroke.

When you say 80:1, 80:1 what? AFR?

 
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I don't want this to become a pressure wave thread, but I'd like to point this out.
Here's a link regarding Caterpillar and Comprex.
Actually Comprex is not a new technology. Saurer a former Swiss-truck manufacturer which also produced the first turbocharged truck 1938 had been testing the Comprex supercharger 1969 already. ABB (former BBC) owned the trademark Comprex and must have sold it to Caterpillar. ABB still sells turbos for very large engines: ABB also built large gasturbines but sold this division to Alstom.
schwee-- Again thanks for the links. I think I understand. By the way what's interesting is that the inventor lived in the same Swiss town where part of ABB and Alstom are still located. And if you look at the wave rotor, it actually works somewhat like a free piston just that the actual piston is missing and substituted by a gas layer.
PJGD-- It appears to me that the Comprex drum is difficult to seal (compared to a shaft in a turbocharger), that the size of the drum and its cells is not really adaptable to different load conditions and that it is definitely more complex to control. But I don't see why the pressure ratio couldn't be as high as in a multi stage turbocharger as long as there's enough pressure in the exhaust manifold. In this case they are mentioning a pressure ratio increase of 3. The exhaust gas compresses the intake gas in a cell directly, so I don't quite see what could limit this process as opposed to a single turbine or a compressor wheel which always have a limited pressure ratio. (I just try to understand it and I'm not claiming the pressure wave supercharger doesn't have a pressure ratio limit.)
 
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SphincterBoy-- The stirling engine has a very low power to weight ratio. In order to recover the waste heat with a stirling engine you might require a stirling engine several times the size of the IC itself.
 
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Schwee, that was afr. Lean as in like dropping a match into an empty gas can. A typical ignition system wont do it but a match will due to the adequate btu's.
 
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sphincterboy-

Honda has received several patents recently for a "Rotary type fluid machine and waste heat recovering device for internal combustion engine". See US Pat. #6,681,738. Don't know exactly what it is for.

Also take a look at patents: 6,945,050 6,884,051 6,862,974
 
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