Control of Tar Cleanup Engine and Power Producing Engine System

A biomass conversion system is disclosed. The system comprises a syngas generator, a cleanup engine and a power producing engine. The power producing engine is coupled to a load, such as an electrical generator. Methods of controlling the power producing engine in response to changes in load are disclosed. In certain embodiments, the air-to-fuel ratio, spark timing, and/or recirculation gases are varied to change the power of the power producing engine. In other embodiments, the power producing engine is throttled by limiting the amount of clean syngas that enters the engine.