--- Water injection VS Steam Injection ---

[Harlan]

The steam dumped in the intake heats the intake. If it were inert it would lower thermal efficiency of the cycle, and with a gaseous fuel source like propane that would be bad. With gasoline it increases fuel vaporization early in cycle and thus increases fuel economy as you said. But steam is not inert in this cycle. The first phase change is steam to water, where the steam dumps most of it's heat to the intake air while condensing into tiny droplets. During compression the heat that would normally be absorbed by the air is absorbed by the water this does not really add efficiency, it just shuffles around the heat, since it initially was wet steam there is more water mass now than there was steam mass at the beginning which allows for more heat to be absorbed than was originally rejected to the air. The extra water in the steam also moderates the temperature of combustion. This continues through combustion and the power stroke finally giving dry steam with exhaust gasses. Yes the thermal efficiency should be much better with a turbo, but this is what I have to work with right now. I am not violating the laws of thermodynamics nor Carnot's heat engine, I'm simply massaging an Otto cycle adding some Rankine elements and creating something slightly new.

As for heating only with engine coolant. I've done steam injection already, albeit badly. It drops coolant temperatures because it removes heat from the cycle because it's wet steam. Using the coolant is self limiting because the steam acts as internal coolant. Exhaust heat is prevalent and free. The only concern is preventing superheat which should be easy enough with a thermocouple and some experimentation.

Still need a turbo to get the biggest gains. Then it would be a true coexisting Rankine cycle.

[ConnClark]

I did some searching and the only thing I could find as a research paper on steam injection into an internal combustion engine was on a diesel. Its only real benefit was on the reduction of NOx. At light loading there was a barely measurable increase in FE but everywhere else it hurt.

Total unicorn IMHO

[maxc]

http://www.youtube.com/watch?v=Im7Pb...ature=youtu.be

[maxc]

I have come across a steam injection system some 8 years ago, put into a 9-litre diesel engined London bus and was pushing out some good speed, so it was claimed. the same system was also put into a large lorry but fuel enomony is far shiodrt of conclusion. I believe I styil have the hard copy somewhere, if anyone is interested, I will scan it and put it up here. The company that marketed this invention is no longer trading.

The product was basically a heat exchanger ( a block of metal with internal channels) bolted to the exhaust manifold. It is connected to a large water tank, trickling a small amount of water into the block and turn in to steam. The steam is then channelled into the intake of the engine. The idea and physic is sound, it does work.

How much energy can be recovered or mpa improvement is still yet to be exploited. Unfornately the company did not servive long enough to make this product to the market place, either through a lack of fund or government red tapes (grant assisted product for the buses and lorries).
__________________
Richard L
aquamist technical support

[drmiller100]

Originally Posted by Air-Hybrid

Harlan:
"Also injecting steam allows you to recoup exhausted heat and preheat your intake at the same time."

Surely this flies in the face of the principles underpinning a Heat-Engine (Carnot).
The only true efficiency gains of HAIs is that improved evaporation of the fuel in warmer air allows for a cleaner burn.

Dumping heat from the exhaust into the intake has (by Carnot) to lower the thermal efficiency of the cycle.

So only in the circumstances where the gains arising from improved fuel evap. outweighs the efficiency losses caused by lowering thermal efficiency should WAI be used. And then the system should only ever be driven by coolant heat - because disposing of the heat in the coolant has it's own efficiency wins (reduced rad opening/aero and coolant pumping), whereas exhaust heat is actually best serving the engine if remaining as hot as possible.

You are exactly right.

Lets say we inject some small droplets of water into the intake. At atmospheric pressure, under most conditions, we would expect some of the water to "evaporate" and cool the intake charge. At part throttle, this effect is negligible, especially at part throttle under cruise conditions.

Once the intake valve is closed, the piston starts coming up, and pressure start rising. A quick glance at vapor pressure charts shows us as we increase the pressure, water vapor will condense into liquid - it "rains" inside the combustion chamber. Another example of this is the water in the bottom of our air compressor tanks - compress the air, and the water condenses.

After the ignition event, temperatures skyrocket. Back to the vapor pressure charts, and we see some of the liquid turns to vapor, keeping the humidity level at 100 percent as the piston goes down. This keeps pressure high, giving more thrust, and actually lowering the temperature of the gasses.

So, in this case, the exhaust gas temperature is actually lower, but the pressure was higher.

The link given shows ethanol and methanol makes more horsepower then gasoline at WOT.

[Harlan]

All that would be true were the compression of air were isothermal. It isn't. Adding the water makes it closer, because as the temperature increase the saturation point goes up. I'm trying my damnedest to wrap my head around this, but these concepts combine to form something very daunting. Too many variables working counter to each other, and adding combustion dynamics makes it much worse.

Also, I've seen the Youtube video. Found it while researching as well as the other one with the Sabb. Also seen writups on gas turbine steam injection. The problem is that nobody has done the kind of injection I'm planning and shared anything more than hearsay. I'd be willing to admit it wouldn't work if I had any proof of that or any logical reason it shouldn't, I'd be willing claim it does work if I had any solid proof of that too. Since I don't have either, I'm trying it until I get it right and have results. I'm not saying it has to be beneficial, just that I want to have actual quality steam injection before I make that judgement. The math seems to work.

[drmiller100]

simply, water collects in my compressor.

therefore, if you compress 40 percent relative humidity hair, the water "rains" out of the compressed air, regardless of how high the temperature gets.

[Harlan]

Water collects in the receiver when it is at low temperature. When the air is compressed it follows Gay-Lussac's law. P1/T1=P2/T2 at 70F or 294k if you compress air from 1bar to 10bar the temperature goes to 2940K or 4832F. This may seem impossible, but it's how the math works. The air never actually reaches this temperature because of the low specific heat capacity of the air and the losses to the compressors cylinder, but the temperature is hot enough to keep the water from condensing. At 10bar the boiling point of water is 453k. Thanks for making me shake the rust off though, been a while since I'd used that information, and it makes everything make a bit more sense here. I was dumb to say evaporation. That only happens quickly before you hit 100% humidity when injecting.

[t vago]

Cylinder compression is modelled as an adiabatic (no heat energy transfer) process. We ignore real-world losses to the combustion chamber surfaces, because cylinder compression typically happens fairly quickly, and because the real-world losses that do occur in this short period of time will not substantially affect the temperature of the compressed air.

Therefore, T1*V1^(gamma - 1) = T2*V2^(gamma - 1)
or
T1 / T2 = (V2^(gamma - 1))/(V1^(gamma-1))
or
T1 = T2 * (V2 / V1)^(gamma - 1)

The quantity (V2 / V1) is also known as the compression ratio. So,

T1 = T2 * CR ^ (gamma - 1)

So, let's set T2 = 32 F or 0 C or 273.15 K. Let's set CR to 9.5. Let's set gamma to 1.4 for air.

T1 = 273.15 K * 9.5 ^ 0.4
T1 = 672.2 K or 399 C or 750 F

Note that the presence of gasoline will lower this temperature somewhat. As the air temperature inside the cylinder rises, it will rise above the evaporation temperature of the gasoline. The gasoline will then absorb heat energy from the air in order to vaporize. This is why extra gasoline is squirted into cylinders at wide open throttle - The gasoline "cools off" the fuel/air mix such that detonation is avoided.

This cooling effect is also why water injection is popular as an anti-detonation mechanism. Water tends to take over 2 times as much heat energy to vaporize as does gasoline. Charge temperatures are reduced by about this much with a water injection setup, as compared to gasoline alone.

It is unrealistic to compare an engine to an air compressor. Water entrapment inside an air compressor is a consequence of concentrating water content as a result of gathering the compressed air inside a pressure vessel. At some point, the water vapor present in the compressed air will exceed the saturation point of that compressed air, and water will condense out.

[drmiller100]

Originally Posted by t vago

C
It is unrealistic to compare an engine to an air compressor. Water entrapment inside an air compressor is a consequence of concentrating water content as a result of gathering the compressed air inside a pressure vessel. At some point, the water vapor present in the compressed air will exceed the saturation point of that compressed air, and water will condense out.

but doesn't an air compressor look a WHOLE lot like a piston engine?

And doesn't a 10:1 compression ratio pretty much equal the final pressure in most compressers?

And if you are arguing the gasoline gets boiled/vaporized, why wouldn't the water reach 100 percent relative humidity for the given pressure/ temperature and do the same?

And if the pressure is 150 psi, the ignition event happens, and the temperature sky rockets to, say, 1200 degrees or so, wouldn't the water turn to steam keeping the absolute pressure up nice and high for the entire piston stroke????