Experimental Investigation of the Natural Gas / Diesel Dual-Fuel Combustion Using a Rapid Compression Machine

Rapid Compression Machine (RCM) is an experimental tool developed to study combustion parameters. It allows to measure cylinder pressure and piston displacement as well as to film combustion through a transparent piston head. RCM is pneumatically and hydraulically driven device and it reproduces a single combustion shot, considering a compression and a partial expansion stroke. The RCM used in this work was originally manufactured for investigate the diesel engine combustion. This paper describes the RCM adaptations made in order to investigate the dual-fuel combustion characteristics of lean natural gas-air mixtures, using diesel fuel as ignition source. The RCM was equipped with high pressure common-rail diesel injection system and a compressed natural gas system. The natural gas and air were introduced in the combustion chamber, prior to compression stroke, and the pilot diesel fuel was adjusted to typical injection timing and durations of Diesel engines. It investigation also presents some comparative results of these two operation modes (original diesel and dual-fuel), regarding piston displacement, start of combustion, ignition delay, pressure rise rate and peak pressure for different fuel injection timings. Additionally, it is presented combustion images captured by a high speed camera to analyze the flame characteristics.