Natural Gas Engine Technologies: Challenges and Energy Sustainability Issue

Abstract

Energy sustainability and environmental issues pose greater challenges on different primary energy sectors as the global energy demand increases and it is projected to further increase with an upsurge in population. On the other hand, energy sources from conventional fossil-based fuels are depleting, forcing explorations in challenging and difficult locations. As a result, the use of alternative fuels received dramatic consideration to substitute these conventional fuels, of which natural gas took the significant share. However, the share of natural-gas vehicles in the current vehicle market is quite small, and it is estimated to be below 5%. This paper reviews the current resource scenarios including proven and potential reserves, current production, and consumption, along with the fueling infrastructure, distribution, and storage. It also provides summary of the development of fuel-injection technologies aimed to enhance the performance of gas engines. More attention was also given to natural-gas engines and their limitations. Parameters affecting the performance and combustion of compressed natural gas (CNG) in spark-ignition (SI) engines are thoroughly assessed, among which compression ratio and injection timing play major roles in the optimization of CNG-fueled engines. Furthermore, different technologies that help close the performance gap between conventional liquid-fuel and natural-gas engines and future directions of the research are presented.

Fuel Switch to LNG in Heavy Truck Traffic

“…It should also be noted that the price of LNG is slightly higher than the CNG because it is technologically more demanding to produce [20]. Overall number of natural gas powered vehicles is still relatively small, and it is estimated to be below 5% of all vehicles [25].…”

A Hierarchical Optimisation of a Compressed Natural Gas Station for Energy and Fuelling Efficiency under a Demand Response Program

“…The station compressor operates between the limits of the quantity of gas in storage with the compressor being switched on at the lower limit to fill the cascade storage, and once the compressor is on, stays on to fill the cascade storage to the upper limit. The compressed natural gas station purchases electricity from South Africa's national utility firm Eskom based on a time-of-use tariff known as the Miniflex tariff (http://eskom.co.za/tariffs) which is priced in South African Rands as 24] p standard = 0.9446R/kWh if t ∈ [9,17] ∪ [19,22] p peak = 3.1047R/kWh if t ∈ [6,9] ∪ [17,19] (60)…”

“…The availability of the infrastructure to deliver CNG to vehicular customers is a major success factor in the growth of CNG as an alternative fuel for the transportation sector [4] because of fuelling convenience considerations [5]. There has been steady growth in the number of commercial fuelling stations in both developing [6] and developed [7] countries, which has corresponded to the increase in number of CNG vehicles on roads. For commercial fuelling stations, vehicles needing refuelling arrive randomly and are required to be filled quickly, hence the fast-fill CNG fuelling configuration has been the prominent design of choice [8].…”

Stochastic Air-Fuel Ratio Control of Compressed Natural Gas Engines Using State Observer

“…Current research results on the efficiency, emission, and combustion performances of CNG engines were reviewed in [10]. A summary of the injection technologies to improve gas engine performance was given in [11], and the injection timing and compression ratio were assessed to be the major factors affecting the combustion and performance of CNG engines. Experimental results on the emission characteristics and performance of a CNG engine that was modified from a port injection SI engine were presented in [12], and the results showed that despite the low-power and high energy consumption, the emissions were improved dramatically.…”