An Experimental Study On Combustion With A Combined Butanol And Diesel Injection Method

The world energy crisis and increasingly serious exhaust gases pollution promotethe development of new combustion technology of engines and research on cleanalternative fuels. In this paper, the combustion with the combined butanol portinjection and diesel in-cylinder injection was studied on a refitted diesel engine.Effects of various injection ratios of butanol and diesel on engine combustion andemissions at different engine speeds (i.e.1400r/min and1900r/min) and loads (i.e.IMEP0.5MPa and1MPa) were investigated experimentally. In addition effects of EGRrates and injection timings of diesel were also investigated.The experimental results showed that, the premixed combustion was prominentwith the combined injection at low engine loads. And the peak engine cylinder pressuredecreased slightly with a mild increase of the maximum pressure rise rate as theinjected butanol amount increased. At high engine loads, diffusion combustion wasmore dominant, and both the peak pressure and maximum pressure rise rate increasedas more butanol was injected, especially at low engine speeds. With an increase ofbutanol amount injected, the ignition delay of the combustion with combined butanoland diesel injection almost remained unchanged while the combustion durationshortened, and the indicated thermal efficiency decreased but kept at40%~50%. Toemissions, the combustion with combined butanol and diesel injection had a very lowsoot emissions level. NOXemissions decreased at low engine loads while increased toa small extent at high engine loads with the increased butanol amount injected. Inaddition, increased amount of butanol injected resulted in CO and HC increasingsignificantly.With increased EGR rates, the peak engine cylinder pressure of combustion withcombined butanol and diesel injection decreased, and maximum pressure rise rateshowed an increasing trend after decreasing firstly. Furthermore, the ignition delayprolonged while combustion duration shortened, with HC emissions increasing afterdecreasing firstly. Under the medium EGR rate of30%, indicated thermal efficiencywas hardly influenced by the change of EGR rates and soot emissions were kept at avery low level. NOXemissions decreased significantly, achieving a decrease extent of70%at30%EGR rate, and CO emissions nearly unchanged along with EGR rates.Beyond30%EGR rate, it resulted in an obvious decrease of indicated thermal efficiency, a quick increase of soot emissions, and a significantly increase of COemissions. When the injection timing advanced, soot emissions decreased slightly withreduce in CO and HC emissions. Advancing injection timing made NOXemissionsincrease significantly, but its influence on NOXemissions was getting weakened withthe increase of EGR rates.In summary, adjusting injection ratios of butanol and diesel according to differentengine loads, and selecting appropriate diesel injection timing, as well as mediumEGR rate could ensure good economic performance of engine while soot and NOXemissions decreasing significantly, and keep CO and HC emissions generated at a lowlevel. This study was a meaningful reference to butanol used on the diesel enginesefficiently with low emissions.