A Review on Opportunities and Challenges of RCCI Combustion Fueled by Hydrogen and Natural Gas

The extensive use of internal combustion engines in transportation, agriculture, and electric power generation leads to a crisis of fossil fuel, and harmful emissions from exhaust gases have an adverse impact on the environment. Hence, to reduce dependence on fossil fuels and to control emissions parameters, researchers are developing various efficient combustion strategies with renewable, clean alternative fuels. Low-temperature combustion (LTC) is a promising strategy to achieve emission reduction and combustion efficiency improvement simultaneously, which is achieved in numerous ways. In LTC, reactivity controlled compression ignition (RCCI) is the most efficient combustion technique that works under a wide range of loads and facilitates the more effective use of different renewable fuels. Although the RCCI reduces the emission of NOx and soot, it additionally produces a significant amount of CO and unburnt hydrocarbon (UHC) emissions. NG (natural gas) in the RCCI engine is able to reduce smoke and NOx , but the emission of CO is increased. Meanwhile, using natural gas with hydrogen (HCNG) in an RCCI engine improves combustion performance marginally and reduces soot, UHC, and CO and CO2 emissions with a minimal increase of NOx . Since HCNG enhances the gas mixture's reactivity by stimulating the generation of OH (hydroxyl) radical, also, hydrogen produces higher temperatures, assisting in the process of oxidation of CO and hydrocarbons. Hence, this work is concentrated on the recent advancements in RCCI engines with HCNG and highlights the challenges involved in operating and commercializing these engines. This review will assist researchers with the features of emission and performance parameters of an HCNG-fueled RCCI engine.