[Gasification] gas quality and engine lifespan?

[doug.williams]

Hi Ken, and Colleagues,

Just to add to this discussion, and clarify a couple of points.

We all work from some sort of knowledge base, but there is a danger in 
quoting antidote stories, or even experiences when the subject turns to 
engines. Not everyone is in a position to know why their engines had 
problems, or discover the cause, and when you begin to add a dated event, it 
can add real confusion.

Here are a few factors to consider regarding engine failure, or short life.

1. Before about 1950, nearly all engine oil was just a plain non-additive 
mineral oil. You changed it every 1,000 mile as a religion. Contamination by 
soot just fell out of the oil and made sludge deposits. Modern oils have 
additive packages, that suspend all solids like soot, and generally do not 
make sludge unless overheated.

2. Old style engines were "run in" before seeking maximum outputs.

3. New modern engines can be operated to red line speeds, or full output, 
and need this to bed the rings.

4. New engines left to idle for long periods, will glaze the bores, and 
suffer diesel fuel dilution of the oil. This makes excessive soot in the 
oil, shortening the oil filter life, and it's pressure by-pass will open so 
the oil can still flow. In doing that, the oil pressure drops about 10 psi, 
and then the thickened oil has trouble reaching all the important places. 
Logging trucks are prone to this condition.

5. LPG fuelled engines can also suffer fuel dilution of the oil, but you do 
not see any soot, They also become very acid, but the oil stays brown 
colour. Producer gas makes the oil darker as it picks up carbon blacks.

6. Most spark ignition engines derate about 50% on producer gas, and that 
alone extends their life if the oil is monitored.

7. Using normal liquid fuel, diesel oil suffer from sulphuric acid formation 
in the oil, and gasoline engines hydrochloric acid. In normal conditions, 
both engines will produce water from the combustion of these fossil fuels 
equal to the amount of fuel consumed, most of it as exhaust gases. Ring 
blow-by, and condensation in colder or start-up conditions, takes the 
moisture into the oil as the last ingredient of acid formation. Two thirds 
(2/3rds) of all engine wear, is not wear at all, but acid erosion.

8. Additional additives are not necessary if you have clean gas. Tar gas is 
very acid, and ultimately will kill the engine. Tar bakes onto valve stems 
making them stick. Tar also is likely to cause engine overheating, as it is 
a high calorific fuel.

9. The best oil for a producer gas engine, is a good diesel engine oil as 
you would use for any diesel engine of your acquaintance.

10. Air filters are often overlooked as a problem source, and as we 
restricted the air supply to suck in producer gas, should be monitored 
closely.  Ten inches (10") WG is considered to be the maximum pressure drop 
across the membrane.

11. Engines with end entry air manifolds are not good choices for producer 
gas. Central entry as for gasoline is best. End entry can generate a 
manifold pulse that causes uneven distribution of the gas to each cylinder. 
This can in turn cause excessive top ring wear, plus big end bearing wear 
out of step with the other cylinders.

12. Failure to cool gas down to at least ambient temperature reduces the 
volumetric efficiency, and heating the gas to control moisture problems 
compounds all of the above problems.

13. Engines with cast iron valve seat inserts will suffer from valve seat 
recession, due to the lack of lubrication in producer gas. This used to be 
the lead additive once used in gasoline, but the advent of superior valve 
seat materials no longer requires this type of lubricant.

14. Dual fuel engines do not tolerate dirty gas, either tar, or carbon 
particles. The hot diesel injector tips attract the contamination and they 
burn on the tip, causing overheating, and sticking of the pintle.
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That just about covers the main points that I noted from recent discussion.

Doug Williams,
Fluidyne Gasification.