Hydrogen generator, a failure as you guys said 2

[Lou Scannon]

At low throttle settings you don't need all the octane that is required at WOT (but you've got it in the tank anyway). Something like H2 to accelerate the burn at low BMEP could indeed enhance efficiency. Going leaner instead of throttling can also lead to improved efficiency.

 

[globi5]

thundair,

hemi is correct.

Saab made a variable compression ratio engine with a maximum compression ratio of 14 in order to take full advantage of the gasoline at low throttle settings:

http://www.saabnet.com/tsn/press/000318.html

 

[globi5]

And of course hydrogen has a higher flame speed than pretty much anything. (Hydrogen is the lightest molecule and steam is also lighter than CO2).

 

[gpara]

All of this is mute because it made NO difference when added to a fuel injected engine.The extra Hydrogen did nothing to enhance the combustion or mileage without modifying the operating system. All these claims are for standard engines with extra hydrogen added.
Gary

 

[globi5]

I don't doubt your test results and the usefulness of these systems sold online.

But I don't think it is impossible to gain anything out of it per se.
As you mentioned, the amount of hydrogen added to the combustion will need to be significantly higher.
And fuel management and throttle control would definitely need to be adapted.

However, it might make more sense to use all that extra electric power to power an electric motor connected to the drive or a supercharger and gain efficiency this way.

 

[MKimagin]

I just wonna start new thread, and fortunately I spot this one. It exactly cover what I have in mind.

I think most people have little understanding when exactly adding extra hydrogen to in regular fuel mixture (gasoline or diesel) will have any impact on general fuel economy.

The only time when you can expect significant improvement in fuel economy with added hydrogen is when the engine is in extreme operational condition. That specially apply when the engine is in high RPM. That mean very short time to perform complete combustion.
I do not think that you will see much of a different in highway driving. You probably will see much bigger difference in city driving. Starting the car from total stop required the engine to go to high RPM. This where combustion become less deficient . And this is the point where extra hydrogen may help.
I so on one of the web sides that sell the hydrogen buster that the old SAAB with turbo have the best improvement in fuel economy. That might have some sense specially in the older cars.

Now to the point that I really wonna talk about.

I read some info about Wankel rotary engine.
The engine have remarkable power to wight ratio.
Mazda by the way did pretty good job on that engine.
I found all that advantages of: low weight, high power , simplicity....
The biggest disadvantage is that this engine use a lot of fuel. One of the reason of that it have difficulty to burn all that fuel. Reason for that is, very short period of combustion, and "inconvenient " shape of combustion chamber (very long and narrow as oppose to piston engine).
The result is high fuel usage (basically a lot of hydrocarbon go un burn thru exhaust).
Mazda solve the problem with high emission of hydrocarbons by using "afterburner" with extra fuel from the tank (that make the millage even worst).
Another solution Mazda did (in there experimental car) is just usage of hydrogen instead of gasoline. That solve all the problem (except come from we can get cheap hydrogen).

The question is.
What will be the impact on Wankel rotary engine fuel economy if extra hydrogen generator was used to improve the speed of combustion?
Should the millage improve?
Should the level of un burn hydrocarbons by reduce?
How much of hydrogen we will need to see the difference if any?

 

[patprimmer]

There are good reasons to start your own thread instead of hijacking some one else's thread.

If you start with the poor thermal efficiency of a rotary, then add some special technology to improve it you can also apply the technology to a piston engine. Youmight close the thermal efficiency gap between rotary and piston but you will not surpass the piston engine.

The three problems with rotary engines and fuel efficiency are:-

Combustion chamber shape. This is somewhat offset by the leading and trailing spark plug arrangement.

Chamber surface area to volume ratio. This is inherent and can't be fixed.

Port timing is fixed and cannot be varied by changing cam or cam timing on the run.

Their advantage is their power density that allows for a smaller motor and as crank speeds are high, the torque is low, so a lighter duty gearbox can be used. This all helps save fuel by reducing chassis weight and maybe reducing friction in the gear box with smaller gears, but at higher speeds.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[globi5]

As far as thermodynamics goes: Wankel engines and gasoline piston engines both adhere to the Otto-cycle.

http://www.grc.nasa.gov/

http://WWW/K-12/airplane/otto.html

So, speeding up the combustion at low loads will improve combustion in both piston as well as a Wankel engine, because it will adhere closer to the ideal Otto-cycle.

In a Wankel engine it will create bigger gains because the extremely high surface area will cool the gases even more the longer the combustion takes.
Also, one other issue with the Wankel engines is the moving combustion chamber, which seperates the heavier gasoline molecules from the lighter air molecules and enrichens one end of the combustion chamber, which obviously also worsens the slower the combustion. This should indeed be less of an issue with hydrogen.

Keep in mind: The Mazda 787B winning Le Mans 1991 with a naturally aspirated Wankel engine did not have a reduced fuel economy compared to its turbocharged piston driven counterparts even though the Wankel engines are generally not known to be economic. This is related to the fact that economy of Wankel engines suffer particularly at low loads and race cars are hardly driven at low loads.

On the other hand though, pumping losses do not really exist with a Wankel engine, because the rotor doesn't work against any pressure in a crank housing. So reducing the pumping losses by opening the throttle and leaning the mixture will not generate the same benefits with a Wankel engine as with a piston engine.

I wish Mazda would release some data regarding the combination of driving its gasoline/hydrogen RX-8 on mainly gasoline and use hydrogen just to speed up the gasoline combustion particularly at low loads. (Obviously they won't, because this was and is not the goal of their project).

 

[globi5]

Oh, btw and still off topic. Wankel engines do have variable port timing - probably even before the piston engines applied it commercially.

Even the very first commercially available Wankel engine in the NSU spider already had variable port timing. 2 intake ports and the second port would open after reaching a certain load and/or rpm.

The Renesis engine in the RX-8 actually has 3 intakes ports (3 on each side: 6 per rotor).
And possibly the only engine (including piston engines) currently produced without port(valve)-overlap (and still reaching max power at 8500 rpm).

Obviously the timing of each port is fixed (and not variable) and they also don't have variable exhaust port timing - but still.