Abstract
To reduce the greenhouse effect, it is important to reduce not only carbon dioxide but also methane emissions. Methane gas can be not only a fossil fuel (natural gas) but also a renewable energy source when it is extracted from biomass. After biogas has been purified, its properties become closer to those of natural gas or methane. Natural gas is an alternative energy source that can be used for spark-ignition engines, but its physicochemical properties are different from those of gasoline, and the spark-ignition engine control parameters need to be adjusted. This article presents the results of a study that considers a spark-ignition engine operating at different speeds (2000 rpm, 2500 rpm, and 3000 rpm) and the regulation of the timing of intake valve closure when the throttle is partially open (15%), allowing the engine to maintain the stoichiometric air−fuel mixture and constant spark timing. Studies have shown a reduction in engine break torque when petrol was replaced by natural gas, but break thermal efficiency has increased and specific emissions of pollutants (NOx, HC, CO2 (g/kWh)) have decreased. The analysis of the combustion process by the AVL BOOST program revealed different results when the engine ran on gasoline as opposed to when it ran on natural gas when the timing of intake valve closure changed. The volumetric efficiency of the engine and the speed of the combustion process, which are significant for engine performance due to the different properties of gasoline and natural gas fuels, can be partially offset by adjusting the spark timing and timing of intake valve closure. The effect of intake valve timing on engine fueled by natural gas more noticeable at lower engine speeds when the engine load is low.