Combustion Process Optimization for Wood Gas Engine of a Biomass Power Plant

Abstract

On the path toward carbon neutrality, decentral small-scale biomass power plants (P < 50 kWel) can play a crucial role in heat and electricity supply and grid stability in areas with rich wood resources. The biomass, such as wood chips, is gasified, and the wood gas is utilized by a small high-speed engine that drives a generator. Due to wood gas properties, the engine applies a fast-burn and ultralean combustion concept at a high compression ratio. However, efficient engine operation is challenging due to specific operating conditions such as low-pressure wood gas supply, fluctuations in gas composition, and low heating value. Hence, the present paper focuses on the combustion process investigation and aims to determine the potential for efficiency improvement and pollutant emissions reduction by applying selective optimization measures such as intake pressure boosting, adaptive combustion control, and spark-assisted autoignition on the related wood gas research engine. The experiments occur on a single-cylinder engine test bench with a fully flexible gas composition mixer. Boosting intake pressure prevents significant engine efficiency losses related to the low-pressure gas supply and gas exchange process. Adjusting the engine operating parameters by a combustion control can compensate for the composition fluctuations and avoid efficiency losses of up to 2%. An efficiency breakthrough is realized by applying spark-assisted compression ignition (SACI) on the naturally aspirated wood gas engine. In the lean engine operation, "Near-Zero NOX Emissions" are achieved, whereby an exhaust gas aftertreatment system can reduce CO effectively.