Investigations of Ignition Delay Behavior in a CFR F5 Cetane Rating Engine and a Modern Heavy-Duty Diesel Engine

The American Society for Testing and Materials (ASTM) D613 test method involves the use of a variable compression ratio CFR F5 engine to determine the cetane number of diesel fuels for use in compression ignition engines. The CFR F5 remains relatively unchanged since its conception, utilizing a swirl prechamber, mechanical jerk fuel pump, and a 10.3 MPa cracking pressure pintle nozzle mechanical injector. Recent efforts to improve the repeatability of the F5 engine involved the development of prototype engines equipped with electronic fuel injection (EFI) and upgraded high-speed instrumentation. These modifications have demonstrated the capability to improve the ASTM D613 precision limits by at least a factor of two. Parameterization of injection strategy has further optimized the test method, producing cycle-to-cycle variations of ignition delay analogous to modern day compression ignition engines. This study aims to expand on these improvements by identifying and quantifying similarities in ignition characteristics between the EFI F5 and a single-cylinder Caterpillar C9.3B heavy-duty diesel engine. Parametrization studies of injection advance and intake air temperature at fixed compression ratio and a gross indicated load of 2 bar were performed on both platforms with reference fuels at varying cetane number. Apparent heat release analysis was performed for the F5 and C9.3B. Despite the different combustion systems, the F5 and C9.3B have very similar ignition delay characteristics as the fuel and operating conditions are varied. This study validates the F5 engines importance and relevance as the primary cetane rating methodology for diesel fuels used in compression ignition engines.