Effect of Polyoxymethylene Dimethyl Ethers-Diesel Blends as High-Reactivity Fuel in a Dual-Fuel Reactivity Controlled Compression Ignition Combustion

To overcome the limitations such as lower combustion efficiency (CE) and higher cyclic variability in methanol/diesel (M/D) reactivity controlled compression ignition (RCCI) combustion, a fuel having higher reactivity than diesel (i.e., polyoxymethylene dimethyl ethers, PODE) was used in our previous study. Methanol/PODE RCCI combustion resulted in improved CE and reduction in soot and unburned emissions compared to M/D RCCI combustion. However, it was noticed that the use of neat PODE as high-reactivity fuel had damaged the fuel line materials frequently due to its higher oxygen content and lower viscosity. In addition, Methanol/PODE RCCI has also resulted in higher NO emissions compared to M/D RCCI combustion. Hence to sort this out, an attempt is made in this study to investigate the effect of PODE-diesel blend on dual-fuel RCCI combustion in order to propose a suitable blend proportion which can tackle the fuel line material damage, increased NO emissions, CE, and cyclic variability. In the present investigation three PODE-diesel blends, namely, PODE10, PODE30, and PODE50, have been prepared and tested at 21 kW and 28 kW fuel energy input (FED conditions. Since the fuel composition has changed from PODE to PODE-diesel blends, to gain similar benefits, experiments have been performed at both early and late injection strategies at a constant combustion phasing (CA50) of about 10 degrees CA aTDC and 20% EGR. The experimental results indicated that a higher PODE blend ratio reduced the cyclic variability and increased CE. Methanol/PODE50 RCCI operation indicated 2% improvement in CE, 2.9% increase in brake thermal efficiency (BTE), and 3.1% reduction in COVIMEP compared to M/D RCCI combustion. However, still the NO emission is marginally higher compared to M/D RCCI combustion and significantly lower than methanol/PODE RCCI combustion.