Combustion Performance and Low NOx Emissions of a Dimethyl Ether Compression-Ignition Engine at High Injection Pressure and High Exhaust Gas Recirculation Rate

Inmo Youn,Joonho Jeon

doi:10.3390/en15051912

Abstract

Dimethyl ether (DME) is a promising alternative to diesel for compression-ignition (CI) engines used in various industrial applications. However, the high nitrogen oxide (NOx) emissions of DME combustion have restricted its use. The primary cause of high NOx emissions is a high combustion temperature. In this study, a high exhaust gas recirculation (EGR) rate was used when testing a common-rail direct injection CI engine suitable (with minor modifications) for a passenger car. A modified fuel supply system created high injection pressure during evaluation of combustion performance. The physical and chemical properties of DME were the principal determinants of the ignition delay, combustion speed, and heat release rate. Although a high injection pressure accelerated formation of the fuel-air mixture and the combustion speed, combustion performance deteriorated with increased NOx emissions. An increased EGR rate affected combustion and the NOx concentration. A high EGR rate effectively reduced NOx formation and emission under low-temperature combustion conditions. Also, the good DME combustion characteristics were maintained when the EGR rate was high, unlike for an ultra-low sulfur diesel engine.

Highlights

Clean energy has become a major issue, especially for of internal combustion (IC)engines
Alternatives to IC engines powered by fossil fuels include electric energy, fuel cells, and engines that use renewable energy, many existing industrial IC engines will continue to be used for some time
Given the lower lower heating value (LHV) of Dimethyl ether (DME), 48% more DME than ultra-low sulfur diesel (ULSD) was required to produce the same energy in the combustion chamber [31]

Summary

Introduction

Clean energy has become a major issue, especially for of internal combustion (IC). engines. Mehra and Agarwal [6] reported reduced exhaust emissions from a DME engine, with low-temperature combustion, using multiple injection strategies. This enabled reductions in nitrogen oxide (NOx) and soot emissions when the combustion temperature is decreased during the combustion process. Multiple injection strategies and exhaust gas recirculation (EGR) effectively reduced the combustion temperature. This work aimed to reduce NOx emissions from the DME engine of a passenger car using a high injection pressure and high EGR rate. DME and ultra-low sulfur diesel (ULSD) were used to investigate the effects of injection pressure and the EGR rate on the combustion and emission characteristics of a CI engine. Chemical formula Cetane number [22,23] Oxygen contents (wt%) Lower heating value (MJ/kg) [24] Boiling temperature (◦C) [25] Liquid density (kg/m3 at 20 ◦C) Liquid viscosity (kg/m·s at 25 ◦C) [26,27] Vapor pressure (MPa at 25 ◦C) [28] Latent heat of vaporization (kJ/kg) [29]

Engine System

Experimental Procedure

Findings

Exhaust Gas Recirculation (EGR)