The effect of outside air temperature and cetane number on combustion and performance in a UAV engine at various altitude conditions

摘要

A multi-cylinder turbocharged direct-injection (DI) diesel engine was tested in the U.S; Army Research Laboratory Small Engine Altitude Research Facility to investigate combustion and performance of the engine at various altitude conditions. The study was conducted from sea level to 7,620 m (25,000 feet), where the outside air temperature (OAT) and pressure were independently controlled to match International Standard Atmosphere (ISA) conditions. Engine tests are conducted using two different specially-formulated Jet A fuels, with cetane numbers 35 and 40. Decreased in-cylinder pressure and engine performance were found as altitude increased. The impact of the ignition quality was found to be significant with higher altitude, as longer ignition delay allowed more mixing of the fuel and air charge, which lead to a rapid combustion. This in-turn increased maximum pressure rise rate (Rmax), and has the potential to cause mechanical failure of an engine or shorten engine life.