LPG Direct Injection Engine for Medium Duty Trucks

This paper provides a summary of a Liquefied Petroleum Gas (LPG) concept engine developed for medium duty applications (class 6-7 trucks) targeting high efficiency with a power density that matches turbocharged diesel engines. The turbocharged in-line 6 cylinder engine incorporates an advanced spark ignition combustion system design, a purpose built medium-duty class engine structure optimized for operation with a direct propane injection system, dual overhead cams with individual cam phasers and twin-entry turbocharger. The high tumble charge motion combustion system targeted for operation with direct injected (DI) LPG has resulted in an engine capable of producing up to 22 bar brake mean effective pressure (BMEP) at high brake thermal efficiency (BTE) throughout the operating map.

The high BTE combined with low carbon to hydrogen ratio of LPG results in 12% lower Brake Specific CO2 (BSCO₂) emissions on the heavy-duty FTP cycle when compared to a diesel engine of same displacement and power and 15-30% lower BSCO₂ when compared to other commercially available medium-duty LPG engines.

The present work demonstrates total cost savings between 1 and 40% (depending on the cost differential between LPG and diesel) over 10 years on a drive cycle represented by the FTP cycle when compared to a diesel engine with similar displacement and torque curve. The ability to run at or close to Maximum Brake Torque (MBT) spark timing along with low pumping losses have ensured high BTE over the entire operating region of the engine.