Effect of injection timing on combustion, performance and emissions characteristics of methanol fuelled DISI engine: A numerical study

Abstract

In this paper, the effect of the start of injection (SOI) on the engine characteristics of a methanol-fuelled direct injection spark ignition (DISI) engine is numerically studied. The simulations are performed using CONVERGE CFD software on a wall-guided, four-stroke gasoline direct injection (GDI) engine. The SOI is swept from −120° CA ATDC (crank angle after top dead centre) to −100° CA ATDC at a constant step of 5° CA. The engine speed of 2000 rpm and a compression ratio (CR) of 11:1 is used. It is observed that there exists an optimum injection timing for a given spark timing at which the best compromise is obtained between the performance and emissions. A maximum indicated thermal efficiency (ITE) of 41.66% is obtained in the case of −115° CA ATDC SOI. Emissions like formaldehyde and soot are also found to be the lowest in this case. Engine's ITE is 36% higher for methanol fuel than gasoline when simulated by supplying the same energy input, keeping all the other parameters the same. The total hydrocarbon (THC), carbon monoxide (CO), and soot emissions are 58.2%, 68%, and 73.9% lower for optimised methanol injection timing as compared to gasoline. The NOX emissions are found to be higher for methanol than gasoline due to higher in-cylinder temperature in the case of methanol engine, which is due to higher heat release and proper combustion than gasoline.