Gas cleaning and cooling
Trouble free operation of an internal combustion engine using producer gas as fuel requires a fairly clean gas (see section 2.1.3).
As has been mentioned in sections 2.3 and 2.5 well designed downdraught gasifiers are able to meet the criteria for cleanliness at least over a fairly wide capacity range (i. e. from 20% — 100% of full load). Up draught gasifiers in engine applications have to be fitted with bulky and expensive tar separating equipment. It is however possible to get the gas from up draught gasifiers up to specification as is reported by Leuchs (26). Methods are under development to reform the gas in a high temperature zone (secondary gasification), in order either to burn or crack the tars.
When suitable fuels are used, the gasifier and cleaner are well designed and the gasifier is operated above minimum capacity, tar contamination of the gas does not present a major problem.
Gas cooling mainly serves the purpose of increasing the density of the gas in order to maximize the amount of combustible gas entering the cylinder of the engine at each stroke.
A ten percent temperature reduction of the gas increases the maximum output of the engine by almost two percent. Cooling also contributes to gas cleaning and makes it possible to avoid condensation of moisture in the gas after it is mixed with air before the engine intake.