[Gasification] Rebuilding engines (was Re: CharcoalGasifier No 2.)

[Ken Boak]

Bob, List

You are correct - cylinder volume to surface area works against all small 
steam (and IC) engines.  Heat losses are significantly larger in proportion 
for the small engine.  Internal friction and bearing losses are also likely 
to contribute too.

Small scale steam is unlikely to make used of multiple expansion stages or a 
separate condensor.

Whilst the model racing hydroplane enthusiasts in the 1940s made extremely 
powerful small steam engines (1 bhp from 1" bore - often competing with the 
best IC engines), it was at the expense of a very powerful gasoline fuelled 
burner and several tens of feet of stainless steel monotube boiler  - 
overall efficiency was very poor - but it was speed that they were looking 
for.

The same can be said for small IC engines,  a 1hp, 22cc strimmer engine is 
likely to be about a third of the efficiency of a typical vehicle engine. 
Fuel consumption figures for these smaller engines are not often available, 
and who really cares if your strimmer brush cutter or chainsaw uses a pint 
more gasoline?

The 3hp Mike Brown engine will quite happily power a 1.5kW generator - but 
consuming about 40 lbs (18.18kg) of steam per horsepower hour.

As it takes 2.2MJ  to evaporate a kilogram of steam, assuming the water is 
already boiling,  then the 3 hp engine will use 18 x 3 x 2.2MJ  per hour  = 
120 MJ  or  33.3kW of energy to produce 1.5kWh of electricity  - in other 
words approximately 4.5 or 5% overall efficient.

This is probably OK if you are running a sawmill or wood processing plant or 
sugarcane refinery and you need loads of heat and you have loads of biomass, 
but it makes no sense at all for the domestic environment when you can use 
an off the shelf  IC engine and get 4 to 5 times this efficiency.

IMHO I think that the ready availability of IC engines will encourage people 
to use these first instead of reverting to the less efficient steam cycle - 
purely because the hardware is just not out there at reasonable cost.


Ken