Influence of swirl on performance and emissions of natural gas heavy duty engines

Generally, nowadays, natural gas heavy duty engines are derived from the equivalent in production diesel ones. As a consequence, they have elevated swirl index, essential for diesel combustion, but not for homogeneous charge spark ignition engines. To improve the benefits obtaining from natural gas spark ignited engines it is primary the development of dedicated engines, according to fuel and its combustion characteristics. Therefore an analysis has been carried out on the swirl ratio (SR) effect on engine behaviour and combustion development. Experimental data have been obtained on a heavy duty engine with two different heads at SR 1.8 and 0.8, and instrumented to acquire the pressure cycle in the combustion chamber. Tests at wide open throttle (WOT) and 50% of maximum load have been carried out. Small benefits on BSFC and volumetric efficiency have been found with the 0.8 SR head.