Theory: not just disabled cylinders, but a power/compound cylinder engine
 

A lot of theories float around this site, mine included, and a lot of time nothing ever comes to fruition, as mods cost money - enough money to prevent the fuel savings offset from benefitting anyone, especially if testing proves that the mod doesn't work.

But, I have another one to ponder. I doubt I'll ever actually try it, but it's an interesting thought. It stems off of the thread where someone wanted to disable half of the cylinders on his engine.

As a side note, engineers have designed ways of capturing lost exhaust energy for quite some time. Turbochargers are one example, but more specificially, using turbo-compounding.
Turbo-compound engine - Wikipedia, the free encyclopedia

It is true that when the piston is nearing BTC and the exhaust valves open, there is still a lot of pressure left over in the cylinder. It is released into the exhaust manifold and basically wasted, because it has simply "run out of time" to produce effective energy. Turbo-compounding was used in WW2, where exhaust gasses would spin a turbine, much like in a turbocharger, but this energy was used to physically help turn the crankshaft, unlike a turbocharger. Currently, the DD15, a heavy duty truck engine, also employs such a design. This engine has a VGT turbo for supplying boost pressure, and also a compound turbo that physically drives the gear train at the back of the engine to supply an extra 50 "free" horsepower. Interesting.

My idea combines the disabling half the cylinders with compound-turbocharging. As an example, I will use my motorcycle, a 400cc four stroke parallel twin.

One cylinder will run normally. It will be called the "power cylinder." The other cylinder will be turned into the "compound cylinder." With some fancy welding and machining, we will add two bumps 180 degrees away from the normal intake and exhaust bumps on the cam lobes, so the valves open twice during one camshaft rotation, turning it into a 2-stroke "air compressor" of sorts, giving it twice the capacity of the power cylinder. The exhaust from the power cylinder is routed through an increased diameter "accumulator", necessary because of mismatched timing between the two cylinders, and then into the intake port of the compound cylinder. The exhaust port of the compound cylinder exhausts to the normal exhaust system.

How it works. Exhaust from the power cylinder, builds pressure in the pipe between the power cylinder exhaust port and compound cylinder intake port. When the air/fuel in the power cylinder is ignited, it expands to maybe five times its volume. The double capacity compound cylinder takes advantage of a higher volume, lower pressure exiting the power cylinder and turns it into energy to drive the crankshaft.

A four cylinder car could be turned into a 2/2 power/compound cylinder engine. Or a V6 into a 3/3. Would it work? Probably. Well? Who knows. I can see compound piston cooling being a big issue, since there would be no cool intake charge to moderate temps. Most importantly: what would we call it? A catchy name is mandatory. Maybe THIS is the question I need to ask!

I was just reading up on a drag race/veteran/engineer named ed donovan, makes racing aluminum engines.

he made a four cylinder to have 5 main bearings, four bolt main caps...because it needs all of it. today, all four cylinders inline are that design...but with two bolt caps or insane japanese mitsubishi types, still committing suicide to performance...anbd 25psi boost too much..just to make up for its own wobbling mass, like a jackhammer..

Aside from having my last name.. it occured to me. They are all crazy.

leave that darned inline four alone..not even a v-twin harley with momentum keepers can keep an engine going for long. An inline for is extremely set and proprietary with balance.. it is hopeless. Save time and money, and leave it alone with all four banging, ya know, up and down up and down with a hopeless hollow backside already....:rolleyes:

I have said it time and time again..the ONLY four cyl that can run on two cylinders and survive.. is a 3 main bearing boxer, with one timing belt removed...and ya know..that is just plain ol ridiculous... a four cyl takes the linear to a revolution at a zero degree loss..that is as small as it can get to maintain fantastic efficiency. :eek:

I do not type this to be mean to ideas.. given my own path and past.. it is just outright ridiculous to ponder.

personally I always liked the idea of just having a couple small engines, i.e. an opposed two cylinder for each drive wheel, and you can shut one off when cruising. with separate paths to the ground you would have ultimate reliability and have a more optimal sized engine for cruising and have twice that much for accelerating. I don't think most current disabled cylinder schemes go far enough, the pistons are still moving, and moving air and causing friction.

I'm not talking about removing pistons or anything, so the primary balance would remain the same. And I'm not talking about getting rid of half the power either. This design, while removing half of the combustion events, would add twice as many expansion cycles. If all went well, there would only be a 30% or so loss of power. And of course, increased efficiency.

Just an idea.

I like this idea.

I have looked at turbo-compund too, which is a really good technique.

There is a guy in india who is currently working for a forklift company. he has strapped a smaller engine next to the bigger ones and the only intake are exhaust gases and fresh air. the result is extra power off the exhaust gases as well as lower emissions.

there is a big issue about fuel burning time (whatever fuel you may be using) and wasted energy.............without looking at the technical details i like the idea.

The problem with stopping the cylinders altogether would be the massive imbalance. You'd shake the engine right off the mounts.

not, as I was suggesting, if they are separate engines, but this might be a hijack in progress.

Edit: moving two engine discussion here:
http://ecomodder.com/forum/showthrea...tml#post170570

You might want to have a look at the Comprex Supercharger developed by Brown-Boveri (Switzerland) and now made by ABB which uses pulse waves to do what your "Compound cylinder" is meant to do IF I am reading your post correctly.

By the way the unlimited development of the turbine to add power to the crankshaft lead to the demise of the piston engine for commercial aircraft !

When the main aim is to use expanding gasses to provide power a turbine is a much more efficient method of doing so.

Peter.

...the Wright R-3350's on our Lockheed Constellation EC-121's used 3 each "power-recovery turbines" (PRT's) that recovered energy from the exhaust from 6 cylinders (3 x 6 = 18 cylinders), to boost total horsepower from 2900 hp up to 3400 hp...that's 500 hp just from exhaust gases at 2,900 engine rpm!

yup, but to Peters point, it wasn't long before they got rid of the piston engine that was between the supercharger and the turbine.

But I'm sure there is work left in standard car engine exhaust fwiw. Problem is extracting the additional heat energy without undue back-pressure (which makes the pistons not want to come back up).

...true, but can anyone cite a "fuel economic" jet engine? I doubt it!

...our R-3350's each burned about 100 gallons of 115/145 AVGAS per hour, which is almost half of what other, non-PRT engines, consumed.

...jet's go thru JP-fuel like 'frat freshmen go thru "free" beer.

I'm not sure if a bit more backpressure really matters. I used to think it does, but not anymore. Any modern diesel engine with a variable geometry turbocharger can have upwards of 50 psi (yes, 50 psi) of exhaust manifold pressure at full load. You would think 50 psi is ridiculously high, especially compared to a naturally aspirated engine with almost zero exhaust manifold pressure, but this pressure is miniscule when compared to the other pressures that make things "go." Combustion pressure can be 2800 psi +. Compression pressure can be 800 psi + at TDC at full load with 35 psi of boost. I'm not sure that a relatively small 50 psi of backpressure means a lot.

I think what killed the piston engine in the airplane wasn't a lack of power and efficiency, but unreliability, complexity, expensive maintenance, and the inability to do high altitude well.

The turbo-compound Napier Nomad held the fuel-specific record for years, and is still ahead of straight turbines because the intermittent combustion allows a higher peak temperature, and with it, better Carnot efficiency numbers. It was just considered too complex.
One thing to consider with the automotive application is that when running at part throttle, the exhaust can be just returning to ambient pressure, leaving nothing for the turbo or second cylinder So this would work best on a very low-powered car. I don't think peak temperatures will be a problem in the second cylinder at any point.

depends on what you call a bit, dont know what engine you are thinking of either, but if it is a 7 litre job, running @ 4000 rpm, putting out 50 PSI, with a bore/stroke of say 4 inches (keep me honest here):

it has to push 50 sq inches of piston area, at 50 psi for 4 inches every revolution

so thats about 2500 pounds of force, for 1/3 a foot or 840 foot pounds per rev

or about 3350000 foot pounds per minute @ 4000rpm, or over 100hp!!

Of course the intake is presumably pressurized too, so that would offset the losses by the ratio of intake PSI to exhaust PSI. i.e. if the intake is at 25psi, you would be spending a total of 50hp just on backpressure. If I figure this right.

Or as a generator, intermittently cycling on @ max load/efficiency for charging.
But doesn't any turbo'ed engine's efficiency increase with load?

Every diesel engine with a VGT and EGR has high exhaust manifold pressure.
A VGT (Variable Geometry Turbocharger) is simple: when the ECM wants more boost, it closes down the volute, much like when you squeeze the end of garden hose. The pressure in the hose increases and the water sprays much farther. When more boost is required, the volute closes, creating a) backpressure, and b) high velocity exhaust that spins the turbine much faster, raising boost levels. VNTs (Variable Nozzle Turbocharger) are slightly different, changing the pitch of the volute fins, but the principle is the same: more restriction = more backpressure + more boost.

Also, backpressure in a EGR diesel isn't a nasty side effect of the VGT, but necessary for EGR to occur. Unlike a gas auto engine, diesel engines require EGR flow at full power where NOX production is extremely high. In order to jam recirculated exhaust into an intake manifold with high boost levels, the exhaust manifold pressure has to be higher than the boost pressure. If is wasn't, EGR flow would be backwards. In the 12-13L and 15L HD diesels, I typically see 40 psi of boost and around 50-55 psi of exhaust manifold pressure at max HP. And lots of EGR flow. This pressure difference between the "hot" and "cold" sides of the engine, combined with an EGR valve for control, is what causes EGR flow in a diesel engine.

Diesels require much more EGR flow than a gas engine to have the same effect, because diesel exhaust contains a higher % of oxygen (which aids combustion, not what you want), and a lower % of inert gas (which cools combustion, what you do want) in comparison. EGR levels in 2007 + diesels (without SCR) are as high as 30% of the intake charge!

I would say that the your calculations for a 7L engine are nifty on paper, but in a real working diesel engine with many things that affect many other things - the kind of things that only engineers know the real calculations for - they are pretty much meaningless. But, so is this entire thread unless someone (AKA myself) actually tries the theory in question.

lol, well psi is psi, and area is area, and since it is measured values the egr doesn't mean anything for these calculations. so you are looking at maybe 20hp in a 13L (large swag), that is to say if you reversed the pressures and put 50psi on the inlet and 40 on the outlet (or any 10psi differential) you could expect 20hp on the shaft then subtract for losses (VE/friction). Pretty far from zero meaning though.

I'm merely trying to point out that backpressure is a very real consideration, not something to be ostracised to the land of magic.

But to your original post, if this DD15 takes ~20hp to make 50hp, then it isn't free, but still a bargain.

Agreed and in most cases piston engines were linked to propellors which limited the top speed of the aircraft whereas the axial flow gas turbine was well suited to both high speeds and high altitudes.

Peter.