CNG engines

[silver343124]

CNG's autoignition point is from 480 to 630 deg C, depends on the methane percentage in the mixture.

So according to thermodynamic equation T2[K]=T1*(V1/V2)^k-1 temperature after compression will be round 660 deg C.

So theoreticaly diesel with added throttle plate and spark ignition could operate with CNG, and if we enclude that CNG is stored under 200-220 bar of pressure and when extracted to the atmospheric pressure or engine boost pressure it will lower the temperature of incoming air and thus lowering the peak compression temperature, that will not exced 630 deg C.

So diesels with lower compression on my opinion could operate with CNG, but I'll gues that the problem will be speed of burning, or from the other point of wiev engine's stroke.

[slideways...]

the burning speed and temperature are the main things that keep companies from making everything compression ignition. its all cool in theory but in practice is harder than most people think. direct injection helps to make gasoline an acceptable fuel for a compression ignition engine because at over 1000 psi, the fuel injected directly into the combustion chamber doesnt create localized hot spots that cause predetonation.

[silver343124]

Originally Posted by slideways...

the burning speed and temperature are the main things that keep companies from making everything compression ignition. its all cool in theory but in practice is harder than most people think. direct injection helps to make gasoline an acceptable fuel for a compression ignition engine because at over 1000 psi, the fuel injected directly into the combustion chamber doesnt create localized hot spots that cause predetonation.

so what you're trying to say?

I really don't get it? Direct injection over common indirect MPI doesn't have a think with compression. It's main reason is to run lean under partial load.
Also DI gas engines has spark ignition like indirect MPI engines, as compression is way too low to self ignite the fuel.

Basicaly my question was is, why CNG operated engines (city buses), don't have higher compression ratio, 17 to 18 almost like diesels.

I know that modified diesel (spark and throttle), will still have too long stroke and will be unsufficent, because gas will burn instantly, while piston will still be in uper 1/3 of position.

But with partial injections, spark ignition and than some more partial after injections it (on my opinion!) could run on CNG.

So basicaly we will inject just small amount of gas (wery lean mixture), ignite it with the spark, and that add 2 to 3 more injection periods to compleate burning.
Of course lean air-gas mixture won't burn, but with stratisfied injection we can attain heterogeneous mixture, where round spark plug will be stoic mixture.

[Moppie]

Originally Posted by silver343124

so what you're trying to say?

He's trying to prove he knows something, and is doing a very poor job of it.


LPG is often added to diesel engines here and in Ausie as a power adder, that also helps with efficiency. Its popular with off road 4WD users as it can extend their range, or give them more power for competition use.


I believe CNG also works, but the LPG works better (care to do the math?) and is more easily obtained here.



The biggest problem with any dual fuel set up of course is the added cost, and the reduction in interior space from the addition of a gas cylinder.
CNG is more flexible than LPG, since you can use several smaller tanks, but they are still intrusive.

[slideways...]

jesus moppie do you have a problem? i was trying to add input but since i dont know a whole lot about CNG setups i was referring to related info involving petrol engines. if you think im way off base just go about it in a logical respectful way. talking down about me just makes you look like the dick.

[Moppie]

Originally Posted by slideways...

jesus moppie do you have a problem? i was trying to add input but since i dont know a whole lot about CNG setups i was referring to related info involving petrol engines. if you think im way off base just go about it in a logical respectful way. talking down about me just makes you look like the dick.

Generally if you don't know what your talking about, its best to keep your mouth shut, or in this case, your fingers off the key board.
Lest you be made to look like a fool.

[slideways...]

i do know what im talking about though. i didnt try and add info about CNG motors because i dont have any to offer. i just was trying to add some tech info to the conversation because no one else was chiming in. flaming someone for trying to have a conversation makes YOU not me look like the fool.

[534BC]

CNG (compressed natural gas) will indeed detonate at 17 or 18:1 ratio whether injected or carb'd. If memory serves me a 14 or 15:1 is about the max ratio for LNG or CNG.

There should be a ton of these engines out in the field hammering away and manuy of them are converted diesels.

"got free gas"?