Intake Manifold Pressure and Exhaust Gas Recirculation Effects on Diesel-Ignited Propane Dual-Fuel Low-Temperature Combustion at Low Loads in a Heavy-Duty Diesel Engine

A 12.9-L heavy-duty (HD) compression ignition engine was operated with diesel-ignited propane. Propane was fumigated into the intake and held a constant 84% of total fuel by energy while diesel was direct-injected at 310 crank angle degrees (CAD). Intake manifold pressure was varied from 135 to 220 kPa (5 to 17.135 psig) for two different exhaust gas recirculation (EGR) valve positions (fully closed and fully open) using a variable nozzle turbo and EGR valve. The engine was operated at a constant speed of 1,500 revolutions per minute (rpm) at constant load of 5 bar brake mean effective pressure (BMEP), which was representative of a typical low load condition for this operating condition (25% full load BMEP). All operating conditions were studied for combustion characteristics, fuel conversion efficiency (FCE), and engine-out emissions. Increasing the intake manifold pressure with a closed EGR valve resulted in lowering brake specific nitrogen oxide emissions (BSNOx) below 0.26 g/kW-h and also decreased brake specific hydrocarbons emissions (BSHC) with the trade-off of higher brake specific carbon monoxide emissions (BSCO) and lower FCE. Increasing the intake manifold pressure with an open EGR valve increased the BSNOx levels at all conditions but also lowered BSCO and BSHC values while increasing FCE relative to closed EGR-valve conditions. An intake manifold pressure of 168 kPa with negligible EGR levels was shown to result in optimal efficiency and emissions levels while applying EGR at the same intake manifold pressure gave an increase of significant FCE with the cost of little gain in BSNOx.