Investigation On Emission Characteristics Of Direct Injection Spark-Ignition Methanol Engine

Methanol (CH₃OH) is considered one of the most promising alternative fuels of internal combustion engine, mainly because of methanol is applicable as gasoline and diesel and also because of its storage and transportation is very convenient and source is very rich. Methanol can extract from coal, natural gas and a variety of crude oil and renewable resources. Among the proven reserves in the world, China's coal accounted for 15%, petroleum accounted for 2.7% and natural gas accounted for 0.9%. Coal Methanol is conducive to the development and use of our abundant coal resources.Although methanol is a good alternative fuel, but except of normal emissions such as hydrocarbon, CO2 and NOx, it also emits formaldehyde (HCHO) and unburned methanol (CH₃OH) when methanol burns in engine.The formaldehyde (HCHO) and unburned methanol (CH₃OH) emissions from methanol engine is much higher than gasoline engines. Formaldehyde can irritate the eye mucous membranes, throat, bronchi and the blood, and it has genetic toxicity and carcinogenic activity. Formaldehyde has the photochemical effect and has strong capacity of destructing the ozone layer, so the concentration of formaldehyde in the working environment should be less than 0.5ppm.In this paper, through burns pure methanol in a direct injection spark-ignition engine and using the self-developed engine control systems investigated the effect of ignition timing, injection timing, lambda and the intake air temperature on engine power performance, normal emissions and abnormal emissions. Meanwhile established collection method of the abnormal emissions of formaldehyde and unburned methanol, and detected the emissions of the formaldehyde and unburned methanol using gas chromatography and HPLC together. The conclusions are as follows: 1. The effect of ignition timing on the power performance and emissionsWith the delay of the ignition timing the torque first rose up and reached the highest value at BTDC 15°CA, and then decreased with the ignition timing delayed on.NOx emission decreased with the ignition timing delayed and the downward trend is obvious, and the overall NOx emissions at low speed and advanced ignition timing are higher. The value of NOx emission decreased rapidly from 1500-2000ppm at BTDC 25°CA to dozens ppm at BTDC 5°CA.HC emission decreased with the ignition timing delayed, but the decline trend is not so obvious, and the values are higher at low speed and the injection timing delayed.The ignition timing has little effects on CO emissions. At high speed and advanced injection timing, the CO emissions postpone downward trend, but in other cases with the delay of injection timing the variation of CO emission is very small.With the ignition timing delayed the emission of unburned methanol decreased and the downward trend is obvious when the ignition timing delayed more. While the formaldehyde emission increased with the ignition timing delayed.2. The effect of fuel injection timing on the power performance and emissions.With the delay of the fuel injection timing the torque declined, and the value is higher at low speedThe NOx emission decreased with the injection timing delayed, and the downward trend is obvious. The NOx emission at 2500r/min is higher than at 2200r/min and 2800r/min.The HC emission is gradually increased with the injection timing delayed, and reached the highest value at 325°CA BTDC, then decreased with the injection timing delayed on, but the change is very small. The value raised only from 265ppm at BTDC354°CA to 282ppm at BTDC 325°CA of 2200r/min in witch the overall emissions highst. It can be supposed that the effect of injection timing on the HC emission is not great.The CO emission is increased with the injection timing delayed, but the change is not great. At 2800r/min in witch the overall CO emission is highest,the CO emission rose from 2.50% at BTDC354°CA to 2.86% at BTDC 310°CA, only increased by 0.36%. Therefore, it can be considered that the fuel injection timing impact on CO emission is not great.The unburned methanol emission increased with the injection timing delayed and the upward trend is obvious, while the formaldehyde emission first increased little with the injection timing delayed and then decreased sharply with the injection timing delayed on.3. The effect of lambda on the power performance and emissionsWhen the throttle opening unchanged, with the reduction of injection pulse width, which means lambda is increased, the concentration of the mixture becomes thinner, so the torque decreased.With the increase of the lambda, NOx emission decreased significantly, and the whole emission is higher at low speed.HC emission decreased first with the lambda increased, the minimum value appeared when the lambda is equal to one, then HC emission rose up with lambda increased on, but the change is not obvious.CO emission decreased obviously with the lambda increased.The emission of unburned methanol increased with the lambda increased, and the upward trend is obvious, while the formaldehyde emission decreased with the lambda increased.4. The effect of intake air temperature on power performance and emissions.The torque changed little with the intake air temperature changed. But the emission of NOx, HC and CO increased with the intake air temperature is raised up. Increasing intake air temperature will raise the normal emissions.The unburned methanol emission decreased with intake air temperature is raised up, while the emission of formaldehyde increased.