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

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 (A) . The results show that as the CDIr increases under lean-bum conditions, the following occurs: the minimum advance for best torque (MBT), the coefficient of variation (CoVIMEF), 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 CNG Direct increase; and torque, peak in-cylinder pressure (Pmax), and the lambda limit first increase and then decrease. The larger the CDIr is, the less influence lambda has on the MBT. When CDIr = 15%, the CoVIMEP can be effectively reduced, the engine can still work stably in all lean-bum conditions, and the A limit will reach the maximum value of 1.73, 19.31% higher than that of the original engine (CDIr = 0). When lambda = 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 lambda. For CA 10-90, torque, and Pmax lambda = 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-bum 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 lambda = 1.1, 15% CDI, 85% EPI combination provides a cutting-edge and outstanding solution for a natural gas/ethanol combined injection SI engine.

Automated summary

Utilizing a dual-injection mode with ethanol port injection and compressed natural gas (CNG) direct injection can enhance the combustion and emission performance of ethanol spark ignition (SI) engines under lean-burn conditions. Increasing the CNG direct injection ratios (CDIr) results in improved engine performance and reduced emissions.