A Study of the Effect of Electronic Fuel Injection on the CFR F5 Cetane Rating Engine - Part II

Over the past few decades, numerous studies have been performed to investigate how to improve the precision of the ASTM D613 Standard Test Method for Cetane Number of Diesel Fuel Oil. Many of these studies concluded that inconsistent combustion is the main contributing factor behind the lack of precision in the cetane number method, followed by shortcomings in the instrumentation used to measure ignition delay. This study is a continuation of recent work that investigated the benefits of installing a high-pressure common rail electronic fuel injection (EFI) system onto a CFR F5 cetane engine. The previous work presented baseline engine measurements that compared EFI against the original mechanical fuel injection system, along with computational fluid dynamics (CFD) simulations of the EFI injection and combustion processes. The previous work also indicated EFI makes it possible to improve the current ASTM D613 cetane test precision limits by at least a factor of two. This study presents subsequent work that was done to characterize the combustion process and optimize the EFI system for the cetane engine. Combustion pressure data quality was improved upon with use of a more sensitive Kistler Type 6054C piezoelectric cylinder pressure sensor, and by increasing crankshaft resolution from 0.144 crank angle degrees to 0.044 crank angle degrees to provide a more precise measurement of ignition delay. High resolution cylinder pressure traces were recorded for several diesel fuels ranging from 40-75 cetane number (CN) under a wide range of operating conditions. Injection advance, ignition delay, and injection pressure were varied to determine optimum conditions for improved cycle-to-cycle combustion stability. Reduced cycle-to-cycle combustion variation results in a more precise measurement of ignition delay, which is the fundamental measurement used to determine the cetane number of diesel fuel. Fuel rate was also varied to study the effects engine load on ignition delay.