Thermal analysis of steel and aluminium pistons in a light duty diesel engine 2019-01-0546
Chromium-molybdenum alloy steel pistons, which have been used in commercial vehicle
applications for some time, have more recently been proposed as a means of improving thermal efficiency in light-duty applications. This work reports a comparison of the effects of geometrically similar aluminium and steel pistons on the combustion characteristics and energy flows on a single cylinder high-speed direct injection diesel research engine tested at two speed / load conditions (1500 rpm / 6.9 bar nIMEP and 2000 rpm / 25.8 bar nIMEP) both with and without EGR. The results indicate that changing to an alloy steel piston can provide a significant benefit in brake thermal efficiency at part-load and a reduced (but non-negligible) benefit at the high-load condition and also a reduction in fuel consumption. These benefits were attributed primarily to a reduction in friction losses. In terms of energy transfer, switching to the steel piston design was shown to reduce heat transfer to the coolant, consistent with lower friction work, and increase the energy transfer to the oil. Piston blow-by was also greatly reduced. Ignition delay times and overall combustion durations were reduced with the steel piston design, possibly indicative of higher piston surface temperatures.
Nick Papaioannou, Felix Leach, Martin Davy