Experiences With CNG and LPG Operated Heavy Duty Vehicles With Emphasis on US HD Diesel Emission Standards

The lengthy experience of TNO with the application of gaseous fuels in engines is discussed. The emphasis is on emissions and efficiency of optimal gaseous fuelled engines in comparison to systems with partial diesel fuel replacement. In spark ignition operation (100% diesel fuel replacement) lean-burn and stoichiometric (electronic control and 3-way catalyst) concepts have been developed. In the optimization mathematical modelling of combustion and flow phenomena is used in combination with engine test bed work. Essential new hardware including micro-electronic control systems is developed. It has been demonstrated on test bed with CNG and LPG that the US HD Diesel Standards of 1994 can be met in the diesel transient cycle. Sufficient lifetime of the system has yet to be demonstrated however. Practical results in different demonstration projects in different countries in the world as well as the application on a practical scale in Vienna (Austria), whereby TNO had an involvement, are reported.