Study on Combustion and Soot Formation Characteristics of RCCI Engine with Diesel Mixed with PODE Ignited Gasoline

Abstract

Article Study on Combustion and Soot Formation Characteristics of RCCI Engine with Diesel Mixed with PODE Ignited Gasoline Qian Wang, Botian Guo, Wenjun Zhong *, Peng Jiang *, and Xu Liu School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, China * Correspondence: wj_zhong@ujs.edu.cn (W.Z.); jiangpeng@ujs.edu.cn (P.J.)     Received: 8 November 2023 Accepted: 23 January 2024 Published: 30 January 2024   Abstract: Polymethoxydimethyl ether (PODE) is a promising clean alternative fuel with the potential to improve carbon emissions from internal combustion engines. However, when used as a sole fuel, its low viscosity leads to increased wear on high-pressure pumps and injectors. Furthermore, its low calorific value makes it unsuitable for direct application in diesel engines. Numerous studies have shown that blending PODE with diesel results in lower soot generation throughout the entire combustion cycle in diesel engines. However, the process of reducing in-cylinder soot generation is not yet clear, necessitating further optical diagnostics of in-cylinder combustion. Therefore, the aim of this study is to investigate the influence of PODE/diesel blend combustion on the combustion characteristics and soot generation properties of reactivity controlled compression ignition (RCCI) diesel engines. The study employs an optical engine and conducts experiments using high-speed imaging and two-color pyrometry. Preliminary experiments indicate that a 50% premixed ratio exhibits better heat release and lower soot generation. Thus, this study explores the effects on in-cylinder combustion and soot generation properties by varying the PODE blending ratio and injection strategy under a 50% premixed ratio. Results indicate that with an increase in PODE blending ratio, both peak in-cylinder pressure and heat release rate decrease, and the combustion duration is prolonged. Compared to diesel, the soot content of P20D80 (20% PODE and 80% diesel) and P50D50 (50% PODE and 50% diesel) is 55.22% and 36.55% respectively, while the heat release is 97.89% and 95.39% of that of diesel. The total amount of soot generated was 55.22% and 36.55% of that of direct injection P0D100, the high temperature area of soot was reduced by 52.9% and 73.32% respectively, the stable value of the average soot temperature was reduced by 6.65 K and 20.25 K respectively, and the average KL factor was the stability values were reduced by 10.35% and 16.12% respectively. P50D50 effectively reduces soot generation while maintaining thermal efficiency. Furthermore, an investigation of injection strategy under P50D50 condition reveals that segmented injection results in lower cylinder pressure, peak heat release rate, and total soot generation compared to single injection. The average temperature of the two-stage injection strategy increased, and the average temperature of soot stable time under the operating conditions of D-40/-20, D-35/-20 and D-30/-20 were 2100.85 K, 2210.16 K and 2192.24 K, respectively. The stable values of the average KL factor of soot under the operating conditions of D-40/-20, D-35/-20 and D-30/-20 were 86.52%, 66.62% and 62.79% of those of S-20, respectively. Although it effectively suppresses soot generation, it comes at the cost of sacrificing a portion of heat release.