Abstract
In this paper, the effect of late injection on combustion and emission levels has been investigated on a single cylinder compression ignition engine operated in dual-fuel mode injecting methane along the intake duct and igniting it through a pilot fuel injected directly into the combustion chamber. During the tests, the amount of pilot fuel injected per cycle has been kept constant, while the amount of methane has been varied on three levels. Therefore, three levels of engine load have been tested, while speed has been kept constant equal to 1500rpm. Pilot injection pressure has been varied on three set points, namely 500, 1000 and 1500 bar. For each engine load and injection pressure, pilot injection timing has been swept on a very broad range of values, spanning from very advanced to very late values. The analysis of heat release rate indicates that MK-like conditions are established in dual-fuel mode with late pilot injection. In these conditions, pollutant species, and NOx levels in particular, are significantly reduced without penalization – and in several conditions with improvement – on fuel conversion efficiency.
Highlights
The natural gas is a mixture of methane, ethane, propane, butanes, pentanes and other hydrocarbons
Even though internal combustion engines (ICE) running on natural gas are characterized by lower nitric oxides (NOx) and particulate matter (PM) emissions levels, they are generally penalized in terms of carbon monoxide (CO) and HC especially at part load compared to conventional diesel engine [1,2]
It can be noticed that misfire was detected at injection pressure of 1000 and 1500 bar with very advanced start of injection (SOI) (-45 crank angle degrees (CAD) BTDC) and late SOI (2.5 CAD ATDC)
Summary
The natural gas is a mixture of methane, ethane, propane, butanes, pentanes and other hydrocarbons. The factor variation ranges leading the engine to operate in HCCI or PPCCI (Partially Premixed Charge Compression Ignition) combustion, i.e., guaranteeing a high conversion efficiency and low emission levels at the same time, were sought and highlighted This suggested that very advanced and retarded injection timings, combined with high ICP, determine very low levels of nitrogen oxides, with little or no penalty on engine. The analysis of heat release rate indicates that MK-like conditions are established in dualfuel mode with late pilot injection In these conditions, pollutant species, and NOx levels in particular, are significantly reduced without penalization – and in several conditions with improvement – on fuel conversion efficiency
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