PODE-blend as pilot fuel in a biomethane dual fuel engine: Experimental analysis of performance, combustion and emissions characteristics

Dual-fuel engines present an opportunity to increase the electric efficiency and fuel flexibility of combined-heat-and-power (CHP) units. It is becoming increasingly important to find alternative liquid fuels, which can be used as a pilot fuel is such units. While being able to be produced from renewable sources, polyoxymethylenedimethylethers (PODE, OME or POMDME) also provide promising combustion characteristics, such as reducing particle matter emissions (PM). However, little knowledge exists regarding the utilisation of these fuels in full-scale engines, as used in CHP-units. Therefore, we investigated the performance, combustion behaviour and exhaust emissions of a dual-fuel CHP-engine operating with biomethane as main fuel and a 50/50-PODE-blend and neat diesel as pilot fuel. The injection behaviour of the PODE-diesel-blends was investigated on a common-rail-injection test-bench. When replicating small injection quantities, as required for pilot injection, the injection rate was found to be almost identical when comparing diesel and the PODE-diesel-blend. The pilot fuel quantity showed to be decisive for performance and emissions of the engine. When keeping the injected energy equal between the PODE-blend and diesel, the NO_X-emissions increased by up to 45% and the PM-emissions decreased by up to 67%, while the efficiency of the engine increased by up to 2.5%.