Small Capacity Producer Gas Engine Adaption from Natural Gas for Decentralized Power Generation Application

Abstract

The adoption of automotive natural gas engine for producer gas fuelled stationary power generation application is addressed and for a target power rating, producer gas fuelled engine performance is compared with natural gas (base fuel) performance. Adoption of the engine from natural gas fuelled automotive to producer gas fuelled stationary system required physical modifications and tuning of the load-throttle-ignition reference map on the electronic control unit which was based on in-cylinder analysis. Adoption of the engine for producer gas fuelled operation resulted in power de-rating of 33% with the 22.5 kWe natural gas rating reducing to 15 kWe. Comparative fuel consumption analysis at loads of 8/10 kWe, which are of interest, indicated specific fuel (biomass for producer gas operation) consumption of 1.51/1.28 kg/kWh for producer gas fuelled operation and 0.398/0.336 kg/kWh for natural gas fuelled operation. The corresponding energy consumption amount to 24.18/20.45 MJ/kg for producer gas and 17.91/15.12 for natural gas at the loads of 8/10 kWe respectively indicating superiority of natural gas fuelled operation over producer gas operation. Analyzing the energy balance, it is observed that the gas to electricity efficiency for natural gas fuelled operation is slightly inferior / on par with producer gas fuelled operation and is attributed to the enhanced part load operation for natural gas as compared to producer gas, adversely influencing the fuel conversion efficiency. Higher cooling load is observed for producer gas fuelled engine operation and is fundamentally attributed to higher thermal conductivity of producer gas due to the presence of hydrogen. On the emissions, the primarily pollutants of carbon monoxide, oxides of nitrogen and unburned hydrocarbons are all well within the prescribed limits for stationary power generating application though the carbon monoxide emissions for producer gas fuelled operation is slightly higher than that for natural gas fuelled operation. Addressing the in-cylinder response, it is observed that the producer gas fuelled operation indicates sluggish heat release, particularly towards the terminal phase of combustion and is attributed to the end mixture cooling due to higher thermal conductivity. Addressing the transient response of the engine, with a recovery time of under 7 seconds for producer gas as compared to 17 seconds for natural gas, superiority of producer gas fuelled operation for transient operation is established.