Methanol is a viable alternative fuel for automotive applications as it can be produced from renewable sources and also has a high hydrogen to carbon ratio. The property of methanol to surface ignite easily can be exploited to use it in a diesel engine even though its cetane number is very low. Such a combustion method can enable the use of 100% methanol by using a properly positioned conventional glow plug (as the hot surface) with respect to the fuel sprays. Continuous energization of the glow plug, exposure to cyclic heating and cooling during different phases of engine cycle, injecting the right amount of fuel in a proper direction with respect to the hot surface for robust ignition at all operating conditions and controlling regulated and unregulated emissions with methanol is a challenge. This technique has not been employed in modern automotive common rail (CRI) diesel engines which provide significant flexibility in terms of injection strategies to run on neat methanol at high thermal efficiencies. The aim of the work presented here is to address these issues and develop a neat methanol hot surface ignition (HSI) through simulation and experimental studies.

First a CFD model of the base CRI engine was developed and validated with experimental data on diesel operation generated during this work. Subsequently this model was modified to simulate HSI mode of combustion of methanol and was validated with experimental data available in literature. The validated model was then used to study the effect of glow plug surface temperature, injection strategies, injection pressure and combustion chamber modification on combustion of neat methanol in the HSI mode. Double Pulse Injection (DPI) with much advanced injection timing of pulse-1 and with equal mass share among the two pulses was found to be ideal for this mode of combustion. Methanol being a volatile fuel, rail pressures around 800 bar was enough to provide good combustion and performance. It was also observed that by shielding the glow plug with a shroud combustion could be enhanced while there were many possibilities for the design of such a shield.

To overcome the continuous energization of glow plug, a novel glow plug control strategy to operate the glow plug at different engine conditions was developed. The glow plug was energized at different voltage levels and its corresponding surface temperature was acquired using an infrared thermal camera. Further a CFD model of the glow plug was developed and was validated with the acquired experimental data. The developed CFD models of glow plug and engine with HSI mode was used to determine the surface temperature required at each engine operating conditions. An Arduino based controller was developed which uses this data to energize the glow plug at the optimized power input. A Patent has been applied for this system (Application No. 202241032094).

A state of the art experimental setup was developed with instrumentation for combustion, performance and for measuring regulated and unregulated emissions using an Euro 6 FTIR instrument. Glow plugs were incorporated at suitable locations in each of the three cylinders. Initially experiments were conducted with methanol blended with butanol that was meant to improve its lubricity. However the higher cetane number of butanol pose certain challenges during the combustion of the blends which were studied through detailed experiments. This led to the selection of a suitable blend of methanol with 70% by mass. DPI injection strategy with equal mass share was found to be suitable with reduced nitrogen oxides-NOx (12% reduction) and smoke (80% reduction) emissions. Slipped methanol and formaldehyde were the significant unregulated hydrocarbon emissions. The slipped methanol could be controlled using an Euro-IV Diesel Oxidation Catalyst (DOC) whereas formaldehyde oxidation was found to be insensitive.

Subsequently HSI mode of neat methanol was conducted first at a speed of 1800 rpm. Many additives like castor oil, lauric acid and stearic acid were evaluated as lubricity enhancers and finally Ethomeen O/12 of 3% by mass added to methanol was found to be suitable. Detailed experiments were done at speeds ranging from 1200 to 2400 rpm and at different BMEPs. The DPI strategy with equal mass share among the pulses along with induction of hot EGR was found to be suitable at higher BMEPs whereas a single pulse injection (SPI) was found suitable for a low BMEP of 4 bar. It was observed that the HSI mode of neat methanol was found to perform better than baseline diesel in all the loads with a significant reduction in NOx (40-50%) and soot emissions (80%). The Total Hydrocarbons (THC) and carbon monoxide (CO) emissions were also significantly oxidized to minimal levels with the help of a Euro-VI DOC which has higher amounts of precious metal than the Euro-IV DOC. Slipped methanol and formaldehyde, which were again the significant unregulated emissions, were both oxidized by the current DOC.

From the experimental and simulation results, it is evident that HSI mode of neat methanol can be successfully incorporated into automotive applications. A suitable strategy to employ either a De-NOx or a selective catalyst reduction (SCR) system for NOx reduction needs to be further incorporated. The results generated can be used are being populated on an automotive ECU for field demonstration.