Combustion and emission characteristics of Multiple Premixed Compression Ignition (MPCI) fuelled with naphtha and gasoline in wide load range

• Naphtha MPCI can operate stably in wide load range from 0.4 MPa to 1.4 MPa of IMEP.
• Naphtha MPCI can achieve high thermal efficiency due to low exhaust loss.
• Gasoline MPCI has low heat transfer loss than CDC and naphtha MPCI.
• MPCI can produce low NOx emissions (<0.4 g/kW h) with the EGR ratio less than 30%.

This paper investigates the effect of naphtha (RON = 65.6) and commercial gasoline (RON = 94.0) on Multiple Premixed Compression Ignition (MPCI) mode. The experiment is conducted on a single cylinder research diesel engine with compression ratio of 16.7. The engine is operated at an engine speed of 1600 rpm for the IMEP from 0.4 to 1.4 MPa. Commercial diesel (CN = 56.5) is also tested in Conventional Diesel Combustion (CDC) mode as a baseline. At each operating point, the injection strategy and intake conditions are adjusted to meet with the criteria (NOx < 0.4 g/kW h, soot < 0.06 m−1, MPRR < 1 MPa/deg and CA50 < 20 CAD ATDC). The typical two-stage combustion characteristics of MPCI are obtained in both naphtha and gasoline. Stable combustion is achieved by naphtha in wide load range, while the engine fuelled with gasoline cannot operate stably at 0.4 MPa IMEP. The COV of IMEP of gasoline MPCI is higher than that of naphtha and diesel. However, gasoline has the low MPRR and the retarded CA50 at medium and high loads due to its longest ignition delay. As a result of low exhaust loss for naphtha and low heat transfer loss for gasoline, the thermal efficiencies are higher for both naphtha and gasoline in MPCI mode than diesel in CDC mode, even though diesel has the highest combustion efficiency. The separated combustion in MPCI leads to low cylinder temperature, and moderate EGR ratio (less than 30%) is needed to control NOx emissions under the limit of EURO VI.