Combustion characteristics of low-BTU gases (about 1000 kcal/N m(3)) were experimentally investigated in order to develop engine generators for waste gasification and power generation systems. Two simulated low-BTU gases, obtained from one-step high temperature gasification (hydrogen rich) and two-step pyrolysis/reforming gasification (methane rich), as well as natural gas, were tested in a small-scale spark ignition engine. Compared to the natural gas driven engine, the hydrogen rich low-BTU gas driven engine showed similar thermal efficiency but with significantly lower NO, and hydrocarbon emissions and wider equivalence ratio range for stable engine operation. On the other hand, the methane rich low-BTU gas engine showed narrower equivalence ratio range for stable operation. The test results show engine performance more depends on combustion characteristics than on the heating value of the fuel gas. For better engine performance, hydrogen rich fuel gas is desirable. (c) 2004 Published by Elsevier Ltd.