Compression ratio is one of the main properties of a reciprocating internal combustion engine defined by its geometry. Typical values are between 8 and 12 for Spark Ignition (SI) engines and between 12 to 24 for Compression Ignition (CI) engines. The ignition in engine operating with producer gas takes place via spark and thanks to a higher octane rating compared to gasoline, it is possible to use engine with a higher compression ratio in order to increase the thermal efficiency of the process. To test the behaviors of the producer gas combustion with different compression ratios four engines were used. Two of them were GM Vortec 3 Liters, with 8.3:1 and 10.5:1 compression ratios respectively, in this case the comparison was based on the exhaust emissions and on the maximum electrical power output reached. The other two were Ashok Leyland 3.8 Liters both with compression ratios higher than the GM engines, which were 12:1 and 16:1. This time, the comparison related mostly to the manifold absolute pressure and to the input from a Bosch Knock sensor. Both the Ashok Leyland engine heads were disassembled from the crankcase in order to inspect pistons and combustions chamber. Results obtained with the two GM engines showed higher performances of the 10.5:1 one in terms of maximum power output compared to the 8.3:1, and similar emissions. The test with the two Ashok Leyland showed lower manifold absolute pressure at the same power output for the 16:1 engine, indicating better performances. During the engine inspection no signs of erosion or wear were observed, confirming the input from the knock sensor about the total or near-total detonation absence.

Proceedings of the 27th European Biomass Conference and Exhibition, 27-30 May 2019, Lisbon, Portugal, pp. 1927-1931