Low-Temperature Natural Gas Combustion Engines

Abstract

Advanced or low-temperature combustion engines have shown the potential to achieve high fuel conversion efficiency with minimal emissions formation and therefore can provide solutions for future powertrain systems. Numerous advanced combustion concepts have been explored, including both spark-ignited and compression-ignited concepts, and each one has been investigated using different liquid or gaseous fuels. This chapter will discuss the potential of using natural gas as a fuel for future advanced combustion engines and will present the associated benefits and challenges. The low carbon-to-hydrogen atom ratio of natural gas can enable a highly efficient combustion process with low CO2 formation; its chemical composition mitigates soot formation during combustion, and its high octane number enables high compression ratio operation of spark-ignited engines with good knock resistance. However, the low reactivity of natural gas inhibits the compression ignition of lean fuel–air mixtures, and any combustion inefficiency may result in direct methane emissions in the exhaust. These characteristics have led researchers to investigate lean natural gas combustion using prechambers (jet ignition), high-pressure direct injection (HPDI) of diesel and natural gas mixtures, micro-pilot injection concepts with premixed natural gas and direct-injected diesel fuel, as well as kinetically controlled and low-temperature combustion concepts such as Homogeneous Charge Compression Ignition (HCCI) and Reactivity Controlled Compression Ignition (RCCI) combustion. This chapter will discuss the use of natural gas in the HCCI and RCCI combustion concepts and analyze the associated benefits and challenges.