4 L Light Duty LPG Engine Evaluated for Heavy Duty Application

Mohammad Ali Khan; Harry C. Watson

doi:10.4271/2010-01-1463

Many applications of liquefied petroleum gas (LPG) to commercial vehicles have used their corresponding diesel engine counterparts for their basic architecture. Here a review is made of the application to commercial vehicle operation of a robust 4 L, light-duty, 6-cylinder in-line engine produced by Ford Australia on a unique long-term production line. Since 2000 it has had a dedicated LPG pick-up truck and cab-chassis variant.

A sequence of research programs has focused on optimizing this engine for low carbon dioxide (CO₂) emissions. Best results (from steady state engine maps) suggest reductions in CO₂ emissions of over 30% are possible in New European Drive Cycle (NEDC) light-duty tests compared with the base gasoline engine counterpart. This has been achieved through increasing compression ratio to 12, running lean burn (to λ = 1.6) and careful study (through CFD and bench tests) of the injected LPG-air mixing system.

The outcome of this work (and others) has stimulated a major Australian Government investment in gaseous fuels consistent with increased home consumption of LPG as over half of local LPG production is exported.

Thus the engine is evaluated in its application to trucks of 15 - 20 tons GVM, needing 170 kW and high torque over the Euro truck steady state and transient test cycles; the European Stationary Cycle (ESC) and the European Transient Cycle (ETC) respectively. It is shown that this engine has the potential to deliver better than diesel CO₂ emissions with relatively low-cost LPG components and likely meeting Euro 5 emission standards with only oxidation catalyst aftertreatment in contrast to the complex aftertreatment needed for diesel engine compliance with the diesel standard (e.g., DPF and SCR using urea for particulates and oxides of nitrogen (NO_x) control).

The paper also comments on the relative merits of liquid-phase, gaseous-phase and throttle body LPG injection.

Efficiency and emissions performance comparison are made with the same engine at a higher compression ratio optimized for compressed natural gas (CNG) and a 6-cylinder Euro 3 diesel engine of similar power. The data indicates that LPG can perform at a thermal efficiency equal to that of the diesel engine, but slightly worse at low NO_x levels. Although CNG has highest efficiency over both ESC and ETC, a significant NO_x control strategy is needed.

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4 L Light Duty LPG Engine Evaluated for Heavy Duty Application 2010-01-1463

SAE MOBILUS