Experimental study addressing the challenges of homogeneous charge compression ignition combustion in a light-duty diesel engine using multiple biofuels

Today's research concerning power generation and transportation applications is focused on sustainable engine technology solutions. Conventional diesel engines could be retrofitted with Homogeneous Charge Compression Ignition (HCCI) technology to achieve the intended sustainability by effectively utilizing low-carbon/carbonneutral biofuels. In the present research, a market-ready prototype of an HCCI engine was developed that could be operated using biofuel-gasoline blends with dynamically varying biofuel proportions from 20-60 vol.%, depending on engine load demand. A fixed quantity (6 vol.%) of commercial cetane improver was blended in fuel to prevent combustion misfiring in HCCI mode. The HCCI mode was operated at ambient intake temperature and naturally aspirated conditions without using any thermal strategy for fuel ignition control. There are problems with adopting a single specific biofuel-gasoline-fueled HCCI combustion: blend separation due to water contamination, the tendency to disrupt the food chain by pressurizing farmers to grow a specific food crop, the corrosive nature of biofuel limiting its proportion in the blend, and lesser flexibility to tune blend properties. These shortcomings were alleviated by proposing multiple biofuel-gasoline-fueled HCCI combustion, which is the novelty of the present study. A case study of the 20% acetone in gasoline blend (20AGE) was presented in which diisopropyl ether or n-butanol was added to replace gasoline, addressing the abovementioned drawbacks. Blending 40% diisopropyl ether to replace gasoline in 20AGE produced a maximum increase in the indicated thermal efficiency (ITE) by 1.8 times. It led to a maximum decrease in smoke, oxides of nitrogen, and carbon dioxide emissions by 52%, 38%, and 14%, respectively than 20AGE at the part load conditions. The Fuel Mean Effective Pressure distribution structure was established for the HCCI mode to find the sources of the energy losses impacting the ITE. The Fuel Interchangeability Index was determined for the HCCI mode, using which the interchangeable biofuel-gasoline blends could be identified, considering their crucial fuel parameters. Overall, HCCI combustion using a suitable combination of multiple biofuel-gasoline blends provides a sustainable solution to operate light-duty diesel engines.