What is the feasability of a motor using both Internal Combustion and steam?
Water circulated through the engine’s water jacket and/or exhaust manifold, heating it to boilingthen injected into a cylinder just after TDC when combustion temps are at their highest.
You mean like a bank of cylinders, some of which are IC (to produce the heat to warm the water jacket) and others of which are driven by steam (from the hot water jacket)? Both turning a common crankshaft? Naaahhhh! Combines the worst of both designs.
I’m a proponent of steam engines (or at least the modernized External Combustion engine), but not this bastardized design. I frankly cannot see how it would work.
BMW Developing Steam Assist Drive Based on Waste Heat Recovery
I think this one acts something like a turbine attached to the crankshaft.
Feasible, but not developed for widespread use yet.
No…IC and Steam in the came cylinder.
Imagine a cylinder head for one cylinder:
A big circle (the diameter of the cylinder) with two smaller circles inside it (the intake valve at the north position and the exaust valve at the south position).
On the East position you would have a spark plug on a gas engine or an injector for a diesel motor.
I propose adding a hot water/steam injector at the west position. Recycling thermal energy otherwise lost out the exhaust pipe.
Boiling hot water is injected into the cylinder just after TDC…fuel combustion *should * be complete by now, and the low volume liquid water would encounter the red-hot combustion chamber and white-hot combustion gases and immediately flash into high pressure steam.
The water can be recondensed and recovered after the exhaust flows through an aftercooler.
The point in time you choose for injecting water is the time of maximum pressure from the fueled explosion. It is this explosion that is driving the piston down. Your water (hot, cold or luke) will have to be injected at a pressure higher than the pressure within the cylinder.
I assume this pressure to be overcome is comparable to that of a diesel injector at just before TDC.
Furthermore, the injector can keep injecting for the entire power stroke: certainly, the pressure is dropping between TDC and BDC.
No-- the pressure before TDC is relatively insignificant, otherwide the piston wouldn’t continue to rise against it. In gasoline engines this pressure is often expressed as a ratio-- you might speak of “an 8 to 1 compression ratio”, or 12 to 1, etc. Lower ratios can use low octane fuels while higher ratios require high octane fuels. (Octane is merely a measurement of resistance to premature detonation, and premature detonation is more likely at higher cylinder pressures.)
The pressure in the cylinder after TDC is orders of magnitude greater. This is the “explosion” that creates the power stroke. It is hardly comparable to presures used for fuel injection. Yes, strictly speaking this pressure should decrease as the piston moves down, since the volume of the cylinder is increasing. But this is an infinitesimal amount. And the actual dynamics of combustion (time to complete the burn, speed of piston movement at engine speed) makes it moot.
There’s no real need to combine these dramatically different engine types. External combustion engines (“steam engines”) have some dramatic advantages, enough to reconsider them in their own right even today.
An EC engine stores its energy as the pressure in its boiler. That energy can be used directly to power an engine. IC engines store energy in their fuel, which can only indirectly provide power.
EC engines produce virtually zero emissions, since the products of complete combustion of hydrocarbon fuels are carbon dioxide, water, and heat. While today we might have additional worries about the co2, it would still be a huge advantage for, say, Los Angeles or other places burdened by smog.
EC engines also need no transmission, since they have a “flat power curve”-- they can produce full design torque at any RPM. They don’t need a “low gear” to get started at low RPM and higher and higher gear ratios as the engine increases in speed. Eliminating this piece of equipment would be a great weight saving, as well as reducing maintenance.
EC engines also do not need complicated, computer timed fuel systems- no carburetor, no fuel injectors, no cam shafts, no distributors, no spark plugs. The boiler can be heated by an open fire, like a Bunsen burner or a gas BBQ grill, fueled by natural gas, coal gas, or even crude oil or vegetable oil. It can even be heated by alternatives, like lumps of coal, kindling wood, or anything else that will burn.
Lots of reasons to reconsider EC as a modern alternative for personal vehicles. No good reason to burden them with the limitations of an IC cycle.
I agree that fuel combustion *should * be completed in a conventional IC engine just after TDC, but there are always incomplete combustion products (pollutants) because nature’s not perfect (gasp!). Adding steam *might * help with that (due to what’s called steam reforming reactions), but it just as easily can make things worse. In this case, my guess is that it would make things worse. Not only are you cooling the reaction, you’re also displacing a significant amount of oxygen. In addition, the water/steam-cooled cylinder walls could end up being colder than in a conventional engine, resulting in additional pollutant formation.
I don’t have a specific cite to point to, but water injection *is * known to improve the power of an engine because (as you point out) the water flashes to steam and adds more volume expansion inside the cylinder. I seem to recall that this method was used in WWII fighter planes to give them extra power in dire situations. Water injection also works for gas turbines, by the way, since they also work through the expansion of the gas.
I think that if you were interested in using steam in conjunction with IC engines, the most practical approach would be simple water injection, similar to what you’re describing, but without the preheat. It doesn’t take a lot of mass to make a difference. My guess is that doing the condensation/repressurization step would probably add so much more weight that it wouldn’t be worth it. You’d have to have a pretty complex control system as well so that you weren’t injecting water (or steam) when the engine is cold or at low fuel flow rates (idle). This would be something that would work best at high speed/high acceleration conditions.
Just found this:
Though, this is a six-stroke engine instead of a 2- or 4-stroke.
And a Wiki article on Combined Cycle powerplants.
The problem with combined cycle powerplants (and for that matter, external combustion engines) is their inherent complexity. The appeal of an Otto Cycle or Diesel Cycle engine is that the thermodynamic action all takes place in one chamber. Oxidizer compression (supercharging and turbocharging) has made significant contributions to engine power and efficiency (and water injection has seen some limited use), but having seperate, coupled thermodynamic processes has required prohibitive complexity and weight for something on the scale of an automobile engine. For a large stationary powerplant gaining even a few percent efficiency from additional cycles is worth the cost, but the weight and complexity for a mobile powerplant has not been worth the effort. (BMW’s hybrid steam cycle heat exchanger is an interesting concept for heat recovery, but it appears, based upon their schedule of ten years to production, that much effort still needs to be dedicated into simplifying and compactifiying the system to fit within the envelope of a passenger vehicle.)
The problem with an external heat source is that you have to contain the energy generated adiabaticallyh (so that it doesn’t leak into the environment) and deliver it efficiently to the heat engine. This is a tricky–though not insoluble–engineering problem.
Stranger
A google search for
“steam injected” gasoline engine -turbine
turns up lots of hits. It has been done many times, there are patents, etc.
w.
Gunnerman’s solution which allows water and naptha to be mixted together (if it’s legit) would be simpler. In WWII, some military aircraft were equipped with a water injection system to increase horsepower on take off.
There was an article about a “six stroke engine” in this month’s Popular Science.
“Water injection systems” introduce water into the fuel/air mixture, not directly into the cylinder. The extra mass of the water adds to the pressure driving the piston, thus increases the engine’s power. But the water is not injected into the cylinder **during ** the power stroke. To do so would still require extreme pressurization of the water. Acheiving that pressurization will require a heavy parasitic load penalty that may exceed any benefit from the steam produced. If you’ve got water at that pressure, probably better to use it directly for work, perhaps in a turbine.
The 6 stroke engine avoids this problem, but as Stranger notes, only by the addition of considerable complexity. There are the usual 4 IC strokes, then another pair of strokes exclusively devoted to steam. Apparently the test engine is a single cylinder which has never been run on a dynamometer (previous cites). I suspect that it will prove extremely difficult to balance the actual power of a fuel fired stroke versus a steam fired stroke. With only one cylinder this doesn’t matter-- the thing will still go around and around. But when more cylinders are added I think he’ll see some issues. In a gas or diesel IC engine, having a “bad cylinder” (one that produces less power than the others) will send you swiftly to the shop. Designing an engine where **every ** cylinder is a “bad” cylinder on every other cycle seems inherently problematic.
I still like EC as a stand alone. As Stranger further notes, there are complexity issues (as well as lubrication of the “dry” cylinders) issues, but these are not insoluble. Trade off this engine complexity against the elimination of complex fuel systems, ignition systems, transmissions, radiators and cooling systems, and the overall complexity (and total weight of the vehicle) is reduced. In addition, recirculating freon instead of water as the phase change medium allows for lower overall pressures for equivalent power, due to their lower boiling point.
CannyDan, concerning the “bad cylinder” problem, is there any inherent reason why the imbalance between the fuel stroke and the steam stroke should be of more impact than the imbalance between either of these and the unproductive intake stroke?
As for the complexity - yes, you need another set of valves, of course. I wonder how this would work with a sleeve-valve rather than conventional valves. 
As I understand it, water injection was used to enable IC engines to run at higher compression ratios (> 11:1), without detonation (“knock”). The higher the compression ratio, the greater the fuel efficiency. however, at CR’s > 10:1, you incread NOx emissions-which is bad.
The WWII aircraft H2O injection systems were to give a temporary power boost 9so a fighter pilot could break free of a persuing aircraft0. they were not meant to be used continuously.
H2O injection systems have been tried on car IC engines, usually with mixed results,most of the time, they are not worth the added complexity.
The intake stroke is merely a result of momentum-- the piston descends because it is attached to the rotating crank shaft and thus to (a) another cylinder(s) to provide the force or (b) a massive flywheel (1 cylinder engine).
A power stroke, explosive or steam expansion, is just that-- powered. The piston is being rammed downward against resistance (presumably the wheels of the car, or whatever). With multi-cylinder piston engines (IC or EC) the cylinders each ideally produce nearly the same force. Although there is a firing order such that each one fires in turn and not at the same time as any other, all are connected to the same crank shaft. So the crank is turning at speed X, as a result of the repeated “hits” it receives from each cylinder.
In the proposed 6 stroke hybrid, the IC strokes attempt to produce this rotational speed X. But the EC strokes are not exactly equal in power to those IC strokes, and each EC “hit” tries to turn the crank at speed X+Y (or speed X-Y, doesn’t matter). This will put the connecting rods, bearings, crank, and main bearings under terrific stress.
Like the 1 cylinder prototype, I suppose it will run. But I’d take no bets on how well or how long.
I’m still not seeing it. Supposing the EC stroke to be less powerful than the IC stroke (the argument works just as well if it’s the other way around) , why is there more stress in the underpowered EC stroke than there is when the crank is just having to drag the dead weight of the piston down the cylinder on the unpowered intake stroke - or when it’s having to ram the piston up against the blocked-off combustion chamber on compression? From where I’m sitting those both look like bigger stresses, yet we cope with them easily.
I can buy the complexity argument, though. And I wonder how much water you need?