Investigation on the fuel spray and emission reduction characteristics for dimethyl ether (DME) fueled multi-cylinder diesel engine with common-rail injection system

doi:10.1016/j.fuproc.2011.01.018

Fuel Processing Technology

Volume 92, Issue 7, July 2011, Pages 1280-1287

https://doi.org/10.1016/j.fuproc.2011.01.018 Get rights and content

Abstract

The aim of this study is to investigate the effects of dimethyl ether (DME) fuel on the engine performance and the exhaust emission reduction characteristics in a DME fueled four-cylinder diesel engine with a common rail injection system, as well as an injection characteristics and a spray behavior. The injection rate meter and the spray visualization system are utilized for the analysis of the injection characteristics and the spray behavior. Also, the modified four-cylinder diesel engine with 1.6 liter engine size is used for the investigation of the engine performance and the exhaust emission reduction characteristics of DME fuel.

Based on the experimental investigation, it revealed that the injection quantity of DME fuel was larger than that of the ultra low sulfur diesel (ULSD) due to the high return fuel pressure at the same injection pressure and energizing duration. In this case, the injection quantity of DME fuel is increased by extension of real injection duration due to return fuel pressure.

In combustion characteristics, the peak combustion pressure and the ignition delay of DME fuel are higher and faster than those of ULSD, respectively. The NO_x emission of DME fuel shows slightly higher than that of ULSD at the same engine load condition, and the soot emission of DME fuel is nearly zero level. The oxygenated component and volatility of DME resulted in HC and CO emissions that were lower than those of diesel.

Research Highlights

► Study on the effects of DME in a four-cylinder diesel engine. ► Injection quantity and spray behaviors of DME and diesel fuel were compared. ► Investigation on the combustion and emission reduction characteristics of DME fuel. ► DME fuel showed a high peak combustion pressure, and fast ignition delay. ► Low emissions (NO_x, HC, CO, soot) characteristics of DME compared to diesel fuel.

Introduction

Recent studies on the reduction of motor vehicle exhaust emissions into the atmosphere have focused mainly on alternative fuels with reduced environmental impact. Among the many types of automotive engines, diesel engines have better engine performance, low fuel consumption and greater power output compared to those of gasoline-fueled spark ignition engines. In addition, to adhere to regulations related to carbon dioxide emissions, the major greenhouse gas that causes global warming, studies in search of alternatives to using diesel and gasoline, along with the development of relevant technologies, are needed urgently in order to improve engine performance and to preserve the environment [1].

Despite the low fuel consumptions and high performances of diesel engines, current diesel engines emit particulate matter (PM) and nitrogen oxides (NO_x) at significantly higher levels than those of gasoline engines. Therefore, diesel engines cannot adhere to meet the requirements of the continually more stringent exhaust emissions regulations. With this in mind, many researchers have researched to develop low-pollution diesel engines, and progressive studies have been conducted on alternative fuels which may produce clean diesel engine emissions [2], [3], [4], [5].

Among alternative fuels, dimethyl ether (DME) has excellent ignition ability due to high cetane number (> 55) and good evaporation characteristics in the combustion chamber. In particular, its auto-ignition capabilities and higher oxygen content in the molecular structure improves the combustion performance and reduction of soot emission from the engine system. In these context, DME fuel as an alternative to petroleum diesel fuel has a low carbon to hydrogen ratio and low formation of particulate matter compared to diesel engine [6], [7].

Due to the DME fuel characteristics such as high cetane number and superior atomization performance, DME fuel can be replaced to the conventional diesel fuel. As a standard of the same injection quantity, DME fuel emitted less NO_x emission compared to the conventional diesel fuel [8]. However, at the standard of the same heating value cases, the NO_x emission of DME fuel is higher than that of diesel fuel because the injection quantity of DME fuel is higher than that of diesel fuel [9], and it has the oxygen contents of about 34.8%. The larger NO_x emission of DME fuel can be easily solved by the application of EGR method [10], [11]. In addition, the PM emissions from DME engines are less than those of diesel engines, as DME has a chemical structure with no direct carbon bonding, and the chemical shows a better evaporation performance. However, despite such advantages, DME fuel has a lower heating value than diesel and is very compressible, which makes it difficult to supply a sufficient quantity in a fuel injected system. Furthermore, DME with a low viscosity has some problems in the gas tightness of the fuel line and the lubricity [12], [13]. Its lubricity is lower than that of diesel, which poses some challenges to the durability of fuel-related devices. Such weaknesses create numerous challenges in building an optimum fuel system that uses DME.

Among DME engine studies, Teng et al. [14] focused on the compression ignition delay of DME fuel and reported that the ignition delay in the engine is short and its evaporation rate is significantly higher than that of diesel. The relationship between compression ignition delay, and pressure and temperature was also established. On the other hand, Sidu et al. [15] determined the spray characteristics of DME using a laser system and compared them with those of diesel fuel. Yao et al. [16] studied the combustion characteristics of DME using a constant volume combustion chamber, a visualization engine, and a high-speed digital camera. According to their experimental results, the combustion period of DME is shorter and the flame temperature was lower than those of diesel.

Many researchers have performed experiments to investigate combustion and emission trends when using DME fuel in a diesel engine. Most of which were based on using single-cylinder engines and mechanical injection pumps [17], [18], [19]. However, for electronically controlled DME fuel injection engines, supplying the DME to the engine is not easy, because the evaporation characteristics of DME differ from those of diesel, its lubricity is very low, and the properties of DME fuel caused dissolving of the sealing material.

With these findings in mind, this work seeks to investigate the combustion and emission reduction characteristics of DME fuel in a passenger car's CRDI diesel engine with an electronic control system. Especially this work is focused on the effect of DME fuel on common-rail diesel engine performance and the emissions reduction capabilities of DME when used in a passenger vehicle diesel engine.

Section snippets

Four-cylinder diesel engine system

Fig. 1 shows the schematic of the DME fueled passenger vehicle, the acquisition equipment for the engine performance, and the exhaust emission analyzer, as well as the DME supply system. The experimental setup consisted of a four-cylinder common-rail diesel engine with 1.582 L of displacement volume(bore 77.2 mm, stroke 84.5 mm) and 17.3:1 of compression ratio, and an eddy current dynamometer(150 kW), and the combustion data acquisition system. Also, the harmful exhaust emissions were measured

Injection and spray characteristics of DME and ULSD fuels

Fig. 3 shows the injection quantity and the injection rate profile of DME and ULSD fuels at the same injection conditions (P_inj = 50 MPa, t_eng = 0.7 ms) in order to analyze the injector characteristics as fueling DME and ULSD fuels. Generally, DME fuel is supplied to the injection system as a pressurized condition; however, ULSD is supplied as the atmospheric condition. In comparison of the pressurized DME (solid circle) and the atmospheric ULSD fuels (solid square), DME fuel shows higher injection

Conclusions

This study investigated the combustions and emissions characteristics of DME compared to conventional diesel fuels in an electronic-controlled four-cylinder ignition engine according to various injection and combustion parameters. The test engine used in this work was a four-cycle passenger car diesel engine with 1.582 L of displacement volume. With the DME fuel combustion in the engine as a parameter, the results of this study were compared to the combustion and emission characteristics of

Acknowledgements

This work was supported in part by the Center for Environmentally Friendly Vehicle (CEFV) of the Eco-STAR project of the Ministry of the Environment (MOE) in Seoul, Republic of Korea and by the Second Brain Korea 21 Project. This work was also financially supported by a manpower development program for Energy & Resources and the project for the development of a clean, alternative-fueled power-train system (10033863-2009-11) supported by the Ministry of Knowledge and Economy (MKE).

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Investigation on the fuel spray and emission reduction characteristics for dimethyl ether (DME) fueled multi-cylinder diesel engine with common-rail injection system

Abstract

Research Highlights

Introduction

Section snippets

Four-cylinder diesel engine system

Injection and spray characteristics of DME and ULSD fuels

Conclusions

Acknowledgements

Journal of Power Sources

Fuel

Fuel

Tribology International

Tribology International

Applied Thermal Engineering

Fuel

Energy Conversion Management

Renewable Engine

Optimum diesel fuel for future clean diesel engines

Production Feasible DME Technology for Direct Injection CI Engine

Low sulfur diesel fuel an enabling technology for future low emitting diesel engines

Can heavy-duty diesel engines fueled with DME meet US 2007/2010 emissions standard with a simplified after treatment system

Atomization characteristics of dimethyl ether fuel as an alternative fuel injection system

Energy & Fuels

Atomization characteristics for various ambient pressure of dimethyl ether (DME)

Effect of EGR on HCCI combustion fuelled with dimethyl ether(DME) and methanol dual-fuels