h a l f b a k e r yNot so much a thought experiment as a single neuron misfire.
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Note: This idea was actually inspired by a youtube video of an 8HP single-cylinder Honda engine that was modified with an old Mercedes turbocharger. The fact that the turbocharger wasn't able to spin very fast because of the low pressure in the exhaust gasses was what let me to think about how that pressure
could be added to, even in small engines.
Looking at the diagram of a turbocharger, it looks similar in design and function to a steam turbine. The only minor differences between the two are that A.) the turbocharger uses the power to generate air pressure while the steam turbine uses power to turn a shaft and B.) the turbocharger uses exhaust gases as pressure while the steam turbine uses steam.
My proposal is pretty simple: on a turbocharged engine when the piston is about halfway up its exhaust stroke, water would be injected directly on to the piston to both cool the engine and generate large amounts of steam (pressure). Now before people comment to say that taking heat away from the engine is a bad thing since it all helps with thermal efficiency, I'd like to point out that the water injection would be instead of a cooling system (the same way the crower 6-stroke works). Now the good thing about the added pressure of steam is that there isn't a direct link between engine heat and RPMs, meaning that as long as the engine is warm, there will be almost the same amount of steam and pressure at low RPMs below the boost threshold as there would be at high RPMs and above the boost threshold. Only downside to this in my mind is that the turbocharger would have to be corrosion resistant, and could therefore be heavier than most. Any thoughts?
Autoweek Article on the Crower engine
http://www.autoweek...1023/THISWEEKSISSUE
[elhigh, Jun 25 2007]
PESwiki article on the Crower engine
http://peswiki.com/...s_Six-Stroke_Engine
Addresses a few of the technical difficulties [elhigh, Jun 25 2007]
Wikipedia article on six-stroke engines
http://en.wikipedia...i/Six_stroke_engine
Crower's mentioned here too. I wonder if the Aermotor eight-stroke is in here somewhere? [elhigh, Jun 25 2007]
US Army direct water injection testing
http://ergosphere.f...ater-injection1.pdf
"A study was conducted on the feasibility of totally cooling a single-cylinder diesel engine by direct injection of water into the combustion chamber." [cajunfj40, Jan 31 2012]
[link]
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Wouldn't much of the water just be expelled with the exhaust gasses before turning to steam? |
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Wouldn't the exhaust system fill up with water/condensate? |
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Not when it hits the piston, which would immediately turn it into very high pressure steam (although this means the water would have to be injected at high psi, I'm thinking diesel injectors). |
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Yeah, I'm thinking that there would be some kind of intercooler to purposely condense the steam into water and pump it back into the tank. The fact that ICEs produce a ton of water in the exhaust would make up for a less than perfect condenser, and would be a benefit. |
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At 3000rpm the exhaust stroke lasts for 0.01 seconds. You are saying inject the water at the halfway point, which would give you 0.005 seconds in which to turn the water to steam. At 6000rpm that would be 0.0025 seconds. |
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That sounds like too short a time for anything but a trivially miniscule quantity of water. |
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If you look at a single RPM then of course. But looking at the fact that the steam would be pulsating as rapidly as there would be exhaust strokes, it's actually a lot. Think of the time in between when the steam is injected as the interuption. At high rpms, the interuption sure doesn't last long between steam injection intervals. |
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MFD - this exact idea has been circulating in both televised and print news recently. The guy who heads up Crower Cams - his name is Bruce Crower - built a gas engine, using a diesel block for greater strength, and devised a six stroke cycle: suck, squash, bang, blow (+water injection at the top of the exhaust cycle), expand, blow again. |
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The reports pointed out that the steam exhaust cycle was blasting paint off his ceiling. That's a great potential source for turbocharging, and I wrote to Crower himself to recommend turbocompounding. |
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[Texticle] - considering that aftermarket high-flow injectors are out there that will deliver ridiculous amounts of fuel (and could be adapted to deliver water), and it doesn't take much water to explode into a very useful volume of high-pressure steam, a trivially miniscule amount of water is plenty. |
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Look it up: I'm attaching several links. |
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Well see, the difference is that the crower engine uses the steam for an additional power stroke while my concept does not. While you wouldn't get the added power of an extra stroke, you would get the full power of the steam harnessed by the turbo and wouldn't have to interupt the gasoline strokes like the crower does. |
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You also wouldn't have the extra power. The Crower cycle delivers two power strokes out of six, versus the old Otto cycle of one power stroke out of four. I know which one I like. |
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The Crower cycle still leaves plenty of oomph for running a turbo. Your idea adds mass and volume to the exhaust flow, what will that do to backpressure? It will also cool the exhaust flow enough to shut down the catalytic converter. The Crower cycle will dump its steam exhaust through a different valve than the combustion exhaust and run the steam through a condenser. |
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//The Crower cycle delivers two power strokes out of six, versus the old Otto cycle of one power stroke out of four.// |
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Well, you got me there. But this idea isn't completely for an all new engine designed just for this feature. It's more an idea for an aftermarket system (so when a street tuner decides to turbocharge his Civic, he'll be able to just install the water injectors and enjoy more power than with just a turbo, plus the benefit of no needed mods to the cooling system). It isn't hard to see that the Crower engine is a better concept than this, but that doesn't mean this idea wouldn't have its advantages. Oh and by the way, thanks for the links. |
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A lot of Honda (for example) engines have four-valve heads. Add the injector and the sparkplug and that doesn't leave a lot of room for the water injector. It's getting crowded in there! |
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To give it full credit, this will definitely cool your engine off some. You could maybe run a high-pressure turbo and get away with pump gas for big power on a budget. The turbo will run cooler too: happy bearings. |
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Okay, at first I was ready to bone this idea because it looked derivative, but now I'm going to bun it. If there's a way to add an injector for water, it looks like it could actually be worth the trouble. |
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//Add the injector and the sparkplug and that doesn't leave a lot of room for the water injector. It's getting crowded in there!// |
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Well, unless the engine is direct injected, there would only be the sparkplug at the head. Since direct injection engines have enough room for the injector and sparkplug (and some engines even have 2 spark plugs), I reckon there must be enough room for a water injector. And thanks for the bun. |
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I love this idea. The only gaping flaw is corrosion. How do you propose to keep the cylinder / piston / valves / everything that is in contact with steam from rusting? I know every IC engine produces water vapor, but I could see steam eating away at the metal. Bun to you sir for the idea. |
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The reason that there isn't a close link between RPMs and temperature is that the cooling system cools to a temperature, not a power level. |
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If you start extracting large amounts of power from the engine by using it to boil water, you will use up the heat stored in the block. Thereafter, your availability of steam will be directly proportional to the power input, and hence boost available at low power will be low, while boost at high power will be high. |
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//I love this idea.// Thank you. |
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The corrosion could be handled simply by making the turbo and its componants from stainless steel or a list of other corrosion resistant metals. |
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Although you would be taking heat away from the block and make the heat directly proportional to RPMs by injecting water, that would only be true if it was injected constantly. Since most cars (even high performance ones) most of the time aren't driven even close to their full potential (and in my system water would only be injected at wide open throttle), that means that there should be a good amount of heat in the engine (the water would only be injected at low amounts all the rest of the time when the engine needs cooling). |
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That system is not so good for turbo life. |
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I know, I guess what I meant is that this system couldn't be as corrosive. |
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could use spray on ceramic? they use it on porous blocks
gd stuff tho!
thanks
Nick |
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The military has studied this for diesels, but AFAIK it has not been implemented in a production unit. The PDF gives details of when in the engine cycle to inject for best cooling with least effect on efficiency, some data on port injection rather than direct injection, effect on emissions, "scrubbing" effect of all that water in the exhaust, even a diagram of a closed-loop system for complete re-capturing of the water used for a closed-cycle water cooling system. Somewhere in there is a bit about ~17.5% more turbo power available via steam generation in the exhaust under certain circumstances. Lots of good data in the link. |
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Note: there is all kinds of declassified documents out there revealing military testing of all sorts of odd add-ons to piston engines. Most of it is old, but still useful as the older engines are usually mostly mechanical, so easier to tinker with for the non-electronically inclined. |
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