Combustion and Emission Characteristics, and Emission Control of CNG Fueled Vehicles

Abstract

Natural gas (NG) is considered as one of the most attractive alternative fuels for vehicles due to its clean-burning characteristics. Rapid growth of urbanization and industrialization has multiplied transport fuel demand worldwide. Vehicle population particularly in metropolitan cities has grown exponentially. Adverse effects of vehicular emissions on the environment and human health have forced regulatory bodies to impose increasingly stringent emission legislations. This has necessitated use of cleaner alternative fuels such as NG in the transport sector. NG fuelled vehicles (NGV) have several advantages such as low photochemical reactivity of the exhaust, zero evaporative emissions, minimized cold-start and low-temperature emissions, and suitability for lean-burn operations. Compressed NG (CNG) vehicles have been used since 1960s and have proven safety record. The most important advantage of NGV is that NG is readily available at low cost worldwide, including many developing countries and technologies exist for its transportation, storage, and distribution systems are well matured. This chapter reviews the state-of-the-art in the NG fueled vehicles, focusing on engine combustion and emissions characteristics of NGVs. Worldwide prospects and challenges of NG as a transport fuel are also included. Technical aspects such as CNG properties, and their effect on engine performance, and emissions are discussed. Hydrogen enriched CNG (HCNG) significantly improves mixture flammability limit thus contributing to lean-burn operation of NG fueled spark ignition (SI) engines. Hence, HCNG has shown to be advantageous over traditional SI engines in terms of fuel economy and pollutant emissions. This chapter provides an overview of recent progress on HCNG fueled engines as well. An overview of the emission control strategies for NGVs is presented towards the end. Finally, main challenges and future R&D required for NGVs are identified.