Diesel fueled generators are widely used to provide electricity in off-grid locations in Canada. Transporting diesel fuel to such generally remote locations is often an expensive endeavor and the cost of the electricity may swell to as much as three times the Canadian national average. This also makes it challenging to reduce the greenhouse gas (GHG) emissions in such locations. One solution is to convert the locally available waste biomass into biogas which can subsequently be used in these diesel generators to offset the diesel use. The objective of this study is to demonstrate the use of biogas-diesel dual-fuel combustion in a small diesel generator and study the effects of the biogas flow rate and composition on its operation. The study is unique in highlighting the challenges associated with the application of biogas-diesel dual-fuel combustion in such small generators which typically operate at high engine speeds.
The study is conducted on a 4.0 kW diesel generator which is powered by a four-stroke, single-cylinder, direct injection diesel engine. The generator’s intake manifold is modified to introduce biogas, and the diesel supply and return lines are rerouted to a separate tank to measure fuel consumption. Tests are conducted at an electrical load of 3.3 kW with the engine running at 1800 rpm. Other measurements include in-cylinder pressure, exhaust temperature and exhaust emissions. Biogas is simulated by combining compressed natural gas (CNG – with ∼95% CH4) from pipeline supply and carbon dioxide (CO2) and nitrogen (N2) from high purity gas bottles.
Three common biogas compositions are evaluated with the biogas flow rate progressively increased. Increasing the biogas flow rate leads to higher hydrocarbon and carbon monoxide emissions in comparison to diesel-only operation, though emissions of nitrogen oxides are reduced. Distinct differences are observed in the performance of the engine when the composition of biogas is changed.