Fuel gas compression

[jcarrr]

We hope to use an automotive style turbocharger to compress fuel gas from an approximately -6 psig source to several psig to supply the engine.

There is no need or desire to turbocharge the spark ignition engine.

We hope to avoid the expense and complexity of controls on the unit. There will be flow through the device under all circumstances.

Despite being a generator person, I understand that turbochargers expect to pass the same, or at least same order of magnitude, mass through the turbine and compressor. This is not the case for this installation. More like 16:1

The turbocharger people I have discussed this with are like deer in headlights.

It seems likely that this application will require a mix and match of parts that are outside the usual range of combinations available off the shelf.

Help please.

Thanks

 

[dcasto]

The typical arrangements for a turbocharger come out that the ACFM entering the turbine are about the same as the ACFM entering the compressor. This means the wheel diameters will be close to the same size. The air compression ratio and the exhaust letdown ratios also are very close so speeds match.

You want to compress the fuel so the inlet ACFM of the compressor is nearly 15 times less, so you would need a compressor that handles 1/15 the volume. Put it this way, If your engine where a 500HP unit, you would need the compressor from a 35 HP unit attached.

Finally, the mole wt of natural gas is about 1/2 that of air, so the compressor would have to put up twice the ft of head which means the compressor will have to spin at a reaaly high speed, so high that the exhaust side would be a problem.

Use a supercharger or like someone else once brought up was use an AC compressor.

 

[jcarrr]

Thanks for the reply decasto, are you saying:

The turbine end must match the engine
The compressor end must matche the load

Examples of 15:1
500:35 HP or 20:1.3 HP

The mole weight of air is about 29, and of methane, 16. The compressor must spin 1.3 X the speed required to pressurize air to deliver the same mass of gas. The problems is compounded by the fact that the smaller compressor end needs to spin much faster than the larger turbine end to perform as rated.

Thanks,

John C

 

[dcasto]

Yeah, you could fool the turbine side by haveing a huge waste gate and only let the exhaust needed to match the fuel rate. That would cost you severly on engine HP.