This Presentation will deal with two different combustion strategies for using methanol in the Homogeneous Charge Compression Ignition (HCCI) mode in a diesel engine. The First part of the work will explain about the HCCI combustion of methanol along with diesel in the dual fuel mode by adapting a novel injection strategy for diesel and the second part of the work will deal with HCCI combustion of neat methanol using port injection. These experiments were conducted on a single cylinder common rail water cooled research engine at a constant speed of 1500 rpm. Methanol was port injected while diesel was injected directly into the cylinder as two pulses – an early pulse (during start of suction) for creating a homogeneous charge and a late pulse (10 – 33 deg bTDC, depending on the output) for ignition. The effects of methanol to diesel energy share (MDES), start of injection of the early and late pulses (SOI-E and SOI-L) and early injected quantity (EIQ) were studied at different loads. An EIQ of about 45% of the total diesel quantity was suitable. The thermal efficiencies in the HCCI mode were higher by about 3% as compared to the CDF operation at mid loads and were comparable near full load. The MDES that could be tolerated was higher in the HCCI mode. The soot emissions were reduced as compared to the CDF mode by 94%, 87.6%, 80.3% and the NOx emissions were reduced by 77.5%, 65.2% and 29.9% at the IMEPs of 5.1, 6.2 and 7.5 bar respectively. However, in the HCCI combustion of methanol emission of unburnt hydrocarbons, carbon mono-oxide, methanol and formaldehydes were higher. Also, this type of HCCI mode was possible without intake air heating or EGR. The full load operating conditions were subjected high rates of pressure rise which resulted in elevated NOx levels. To control the rate of pressure, rise and knocking, Post injection strategies were implemented. A low post injection quantity of 2mg/cycle with injection timing of 10 aTDC reduced the NOx, smoke, HC and CO emissions while maintaining the thermal efficiency.
The next phase of the experimental studies explored the potential of using neat methanol in the HCCI mode in achieving low emissions and high thermal efficiency will also be discussed. Here methanol was port injected in order to form homogenous mixture and gets auto-ignited with help of higher intake air temperature (IAT). The HCCI combustion of methanol was demonstrated over the different operating load ranges (25% to 75% rated engine load) with suitable IAT. However, higher load operation using port injection was limited by severe knocking. This experimental study reveals the potential of achieving almost zero NOx and smoke emissions with methanol till mid load which increases with the increase in the load. However, the unburnt hydrocarbons and unregulated emissions (Methanol and Formaldehyde) from methanol were higher and was the major concern with neat methanol HCCI operation. Full load operation with neat methanol was achieved using direct common rail injection of methanol with port injected methanol. The direct injected methanol helps in suppressing the rate of pressure rise and controls knocking. The effect of intake charge temperature, premixing ratio of the port injected methanol, injection pressure and timing of the direct injected methanol along with EGR were studied in detail. With suitable injection strategies for the direct injected methanol, full load operating conditions were achievable with lower NOx and soot emissions. On the whole, operating strategies for neat methanol operation were arrived at all the operating conditions for high thermal efficiency, low NOx and significantly low soot emissions.