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Bio-mass fuel gas is very important because bio-mass gas is renewable and carbon free. Especially, woody chips are very popular and are not used efficiently. Gasifier makes the producer gas from woody chips. Conventionally, dual fuel engines are used to generate electricity by producer gas and light oil. As the dual fuel engine can run under the low heating value gas, dual fuel engine is very useful. As light oil is fossil oil, it is not carbon free. If bio-mass gas engine can run only by producer gas, this power unit is carbon free. As the heat value of producer gas is very low and fluctuates always, bio-mass gas engine should be controlled A/F precisely. As the producer gas contains of hydrogen from 15 to 18%, NOx should be higher on concentration of 15 % hydrogen. Output of bio-mass gas engine should be low because of low heat value of producer gas. The three way catalyst can reduce NOx and CO. Stoichiometric mixture can make output higher than lean burn.

To control natural-gas HCCI combustion, internal exhaust gas recirculation (EGR) by exhaust valve reopening (EVRO) during the induction stroke was applied to a single-cylinder test engine. The results demonstrate that combustion phasing can be controlled successfully by adjusting the EGR ratio, and so improvement of thermal efficiency and reduction in unburned exhaust emissions are feasible. In addition, the results of the EVRO method were compared to those of intake-valve pilot opening (IVPO) during the exhaust stroke. It was shown that EVRO is more useful than IVPO as a heat-recovery method for HCCI combustion.