[Gasification] Engine knock

[doug.williams]

Hello Harmon,

You asked:

>    What about just methane (or rather biogas) in a diesel?

Methane is much the same as CO, or H2, in that it has a spontaneous ignition 
temperature of 1170-F, and will need nothing over 16:1 to work in an engine.

>There seems
> to be a lot of talk in the trucking industry lately about running on
> compressed biomethane, and I know some people use propane injection in
> their diesels for extra power. Any idea what the compression limits
> would be there?

It is easy for people to talk about these issues, and easy to get a funded 
project from the less informed agencies, than it is to make it happen, at 
least in the economy you would hope to achieve. The same would apply to all 
engines that were not set up for duel fuel used in a variable load situation 
(trucks).

Back about 1978-9 here in New Zealand, forestry trucks were set up using 
propane as supplementary fuel with diesels. It was established that the 
maximum replacement ran about 38%, which might be OK to some, but not 
forgetting the potential problems that can be experienced. Some engines take 
it better than others, and if you think about melted pistons,you need some 
real expertise to do it correctly. I am out of touch with those doing that 
work, but the technology has been exported around the World, converting bus 
fleets. Nothing is new, except the need to replace as much diesel as 
possible, given the renewed interest in gaseous fuels.

The reason for the minimal replacement, is that the gas/air ratios change 
across the load range, and this needs a quality close tolerance governor. 
With the advent of computerized systems, it should be easier to sort out 
these truck gas systems, but then again, I have found very few technical 
people who can get their head around the combustion phenomena. As an example 
of this, we were supplied a gas conversion kit last year from the USA, and 
after a lot of mucking about, turned out to be only a version of metered 
supply, not appropriate for variable loading. And it only cost $12,000 
!!!!!!!!


>   Maybe it would be better to run a digester for the genset and reserve
> the woodchips and gasifier for direct heat of a boiler. Or steam, I
> suppose.

Horses for courses Harmon, just sort out the difference between a gas 
producer, and a close coupled combustor.

Regards,
Doug Williams,
Fluidyne Gasification.