Experiments with Wood Gas Engines 2001-01-3681

The utilisation of producer gas - from thermal gasification of biomass - as a fuel for spark ignition gas engines is of vital importance to the ongoing effort of making biomass gasification a commercially feasible technology.

Tests have been carried out with a 1.1 litre four-cylinder natural aspirated SI engine in conjunction with a two-stage gasifier with a nominal thermal input of 100 kW. The fuel-gas is produced from wood chips in order to get a CO₂ neutral fuel for combined heat and power production. The producer gas has a very low tar and particulate content and high hydrogen content. As the gasifier was operated with varying fuel properties, engine tests were made with different fuel-gas compositions. The engine tests showed that producer gas has a power and efficiency advantage compared to natural gas when operating the engine at lean burn conditions. The engine was operated at air/fuel ratios varying from stoichiometric to extremely lean burn (λ>3). This was done while maintaining a good efficiency and power output.

A gas-mixing apparatus was fabricated in order to make synthetic producer gas. With this apparatus, engine experiments were possible, without starting up the gasifier. Experiments have been conducted with a 0.48 litre one-cylinder high compression ratio SI engine fueled by synthetic producer gas, natural gas and a mixture of both. The engine has a detachable piston crown. Different combustion chamber configurations, compression ratios and fuel-gas compositions have been tested.

It has been shown that it is possible to operate the engine at a compression ratio of 16:1 without experiencing knocking.

By using a fuel mixture of 50 v% producer gas and 50 v% natural gas the unburned hydrocarbon emissions from the engine were reduced by up to 70 % compared to natural gas.