Study on Combustion and Emissions of a Combined Injection Spark Ignition Engine with Natural Gas Direct Injection Plus Ethanol Port Injection under Lean-Burn Conditions

Abstract

Conventional ethanol spark ignition (SI) engines have poor fuel atomization and mixture formation. The objective of this paper is to improve the combustion and emission performance of ethanol SI engines under lean-burn conditions through the dual-injection mode with ethanol port injection and compressed natural gas (CNG) direct injection (CDI+EPI). This paper studies the engine performance at 1500 rpm under five CNG direct injection ratios (CDIr) and five excess air ratios (λ). The results show that as the CDIr increases under lean-burn conditions, the following occurs: the minimum advance for best torque (MBT), the coefficient of variation (CoV IMEP ), and CO and HC emissions decrease; the crankshaft rotation or time with cumulative heat release rate ranging from 10% to 90% (CA 10–90) and NOx emissions first decrease and then increase; and torque, peak in-cylinder pressure (Pmax), and the λ limit first increase and then decrease. The larger the CDIr is, the less influence λ has on the MBT. When CDIr = 15%, the CoV IMEP can be effectively reduced, the engine can still work stably in all lean-burn conditions, and the λ limit will reach the maximum value of 1.73, 19.31% higher than that of the original engine (CDIr = 0). When λ = 1.1, CO emissions decrease the most and HC emissions decrease the least. At this time, CO and HC emissions decrease by 1.56 vol % and 30 ppm, respectively, on average for every 0.1 decrease in λ. For CA 10–90, torque, and Pmax, λ = 1.1, 15% CDI, and 85% EPI is the optimal combination under lean-burn conditions. When CDIr ≥ 15%, NOx emissions are at an ideal level. Under lean-burn conditions, direct-injection CNG can form a good stratified natural gas/ethanol mixture in the cylinder, effectively improving the engine’s power and stability and reducing emissions. The λ = 1.1, 15% CDI, 85% EPI combination provides a cutting-edge and outstanding solution for a natural gas/ethanol combined injection SI engine.

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“…However, as a newly developed system, the CNG engines have many drawbacks that can be overcome to optimize the engine performance. To enhance the thermal efficiency of natural gas, it is necessary to overcome two major problems which are low concentration and slow burning velocity [5]. Improving the burning ISSN 2734-9381 https://doi.org/10.51316/jst.167.etsd.2023.33.3.1 Received: December 7, 2022; accepted: March 28, 2023 velocity of CNG engines is quite difficult because the gas motion in the combustion chamber is complicated with the variation of kinetic energy continuous [6].…”

Study on Effect of Piston Bowl Depth on Intake Air Flow Behaviour Using Ansys Fluent Cold Flow

“…However, as a newly developed system, the CNG engines have many drawbacks that can be overcome to optimize the engine performance. To enhance the thermal efficiency of natural gas, it is necessary to overcome two major problems which are low concentration and slow burning velocity [5]. Improving the burning ISSN 2734-9381 https://doi.org/10.51316/jst.167.etsd.2023.33.3.1 Received: December 7, 2022; accepted: March 28, 2023 velocity of CNG engines is quite difficult because the gas motion in the combustion chamber is complicated with the variation of kinetic energy continuous [6].…”