Elsevier

Energy

Volume 39, Issue 1, March 2012, Pages 375-387
Energy

Effect of early injection strategy on spray atomization and emission reduction characteristics in bioethanol blended diesel fueled engine

https://doi.org/10.1016/j.energy.2011.12.050Get rights and content

Abstract

This study is to investigate the emission reduction characteristics of bioethanol blended diesel fuel at early injection condition including spray, atomization and evaporation characteristics. The spray atomization and evaporation characteristics were investigated using spray visualization system and KIVA-3V code, respectively. In this work, the effect of ethanol blending on the spray behavior is more evident at early injection condition. In the calculation results, the droplet size of bioethanol blended fuel was smaller than that of diesel, and bioethanol blended diesel droplets firstly evaporated by its volatility and superior atomization characteristics. In early injection condition, the bioethanol blending caused an increase in indicated mean effective pressure with an extension of the ignition delay. The cooling effect of the bioethanol fuel reduced NOx. The HC emission increased and the CO emission decreased because of the ethanol blending. The geometry mean diameter and total number density increased as a result of ethanol blending, the particle number in the nuclei mode decreased, and the particle number in the accumulation mode increased in early injection condition.

Highlights

► The overall spray, combustion and emission characteristics of bioethanol-blended diesel fuel are measured. ► Experimental results are compared in the early injection- and the conventional injection cases. ► Atomization and evaporation characteristics of diesel-bioethanol blended fuel were numerically analyzed using KIVA-3V. ► In the early injection cases, the cooling effect of bioethanol fuel is clearer compared to the conventional injection. ► By the early injection strategy with bioethanol blended diesel fuel, the exhaust emissions can be significantly reduced.

Introduction

Diesel engine technologies are advancing rapidly with the increase in the needs for clean and high-efficiency fuels. Because of emission regulation strictness, the clean diesel combustion technologies such as the HCCI (homogeneous charge compression ignition) [1], [2], [3], the dual fuel injection strategy [4], [5], [6], and the low-temperature combustion with high EGR (exhaust gas recirculation) rate [7], [8], [9] have been introduced by many researchers. Additionally, with the limitation of fossil fuel reserves, investigation of blended fuels such as diesel-biodiesel and diesel-ethanol fuels is being actively pursued by various research groups. Ethanol fuel can be fermented and distilled from biomasses, and it contains an oxygen atom and thus can be viewed as a partially oxidized hydrocarbon.

Recently, ethanol blended diesel fuels have been used in CI (compression ignition) engines. Diesel-bioethanol blended fuel used in the present study has several advantages including improvement in the atomization performance, the reduction of diesel NOx (nitrogen oxides) emission, the possible improvement in cold flow properties imparted by the bioethanol, the possible improvement in fuel lubricity imparted by the emulsifier additives, and the reduction of fossil fuel dependence. In addition, the direct blending of bioethanol fuel provides higher oxygen concentration than biodiesel blends and higher potential for particulate emission reduction. However, the diesel-bioethanol blended fuel has some significant weak points: phase separation between the diesel and ethanol fuel, a reduction in the cetane number, a higher volatility, and lower miscibility [10], [11]. Many studies have been conducted to find a solution to the phase separation of diesel-ethanol blended fuel, and results have shown that the phase separation problem can be solved by additives [12], [13]. Recent research reported biodiesel fuel as a good additive for preventing phase separation [14]. Additionally, the use of biodiesel fuel is thought to increase of cetane number. Ethanol blended diesel fuel brings the added benefits of reducing diesel PM (particulate matter) and CO (carbon monoxide) emissions from the engine. The results of a study of vaporized ethanol addition to a diesel engine, showed 20%–40% PM reductions and 20%–30% CO reductions [15]. However, the use of ethanol blended diesel fuel also raises concerns related to potential adverse effects on engine and vehicle performance. Ethanol blended diesel fuel has a lower volumetric heat content (MJ/L), therefore some engine power loss will be experienced unless the fuel pump capacity can be increased. Other concerns are related to a loss of engine efficiency and overall performance due to the lower cetane number of the ethanol blended diesel fuel [16].

Lapuerta et al. [17] investigated the emission from diesel-bioethanol blend in an automotive diesel engine. They revealed that the biodiesel blended diesel fuel emitted low soot and low PM emission. In addition, the brake specific fuel consumption increased when using bioethanol blends, and the brake thermal efficiency increased due to its low heating value. In the analysis of particle distribution, the biodiesel blends caused the reduction of the mean particle size. Yan et al. [18] investigated the combustion and emission characteristics of a diesel engine fueled with ethanol-diesel blended fuel in a single cylinder diesel engine. They reported an increase in the ethanol blending ratio caused longer ignition delay, retarded peak combustion pressure timing, and increased the pressure rise rate because of the low cetane number, fast evaporation, and large latent heat of ethanol fuel. In addition, they also reported different NOx emissions results according to the engine load, and HC (hydrocarbon) and CO emissions increased with an increase in the ethanol blending ratio. Sayin et al. [19] numerically analyzed the effect of ethanol-diesel blended fuels on diesel engine performance, combustion, and exhaust emissions. They reported that the brake specific fuel consumption decreased, the brake effective efficiency improved significantly, and the brake effective power increased slightly as the percentage of ethanol in the mixture increased. In addition to these studies, research regarding the fuel properties and combustion characteristics of ethanol blended fuels are consistently being conducted. Armas et al. [20] evaluated the influence of the fuel (diesel and ethanol-diesel blends) used during different transient sequences on the particle size distribution in a city bus. They reported that the use of ‘E-diesel’ (ethanol blended diesel fuel) leads to a slight decrease in NOx emissions in all operating areas. Additionally, the authors reported that the use of ‘E-diesel’ leads to a reduction in both the number and size of the accumulation mode particles, thus causing a decrease in both total particle concentration and total mean diameter, although a significant increase was found in the nucleation mode particle concentration. Excluding the above-mentioned investigations, there are numerous studies on the reduction of exhaust emissions and the mixing stability of ethanol-diesel blended fuels [21], [22], [23], [24]. The authors also conducted the investigation on the combustion and exhaust emissions characteristics of diesel-bioethanol blended fuels, as well as the study on the spray and atomization characteristics [25], [26], [27], [28].

Based on our previous research, authors conducted the numerical simulation on atomization and evaporation characteristics of diesel-bioethanol blended fuel. In addition, the combustion and exhaust emissions characteristics were measured and analyzed when applying the early injection strategy with bioethanol blended diesel fuel that has a lower ignition property, low LHV (lower heating value), and large latent fuel heat. In order to improve the vaporization of the blended fuel spray, the effect of early injection on overall spray behavior and combustion characteristics (e.g., combustion pressure and heat release) of bioethanol blended diesel fuel were investigated. Final purpose of this study is to investigate the emission reduction characteristics of bioethanol blended diesel fuel at early injection condition.

Section snippets

Test fuels and injection system

In this investigation, two test fuels such as pure diesel and diesel fuel with 20% bioethanol were used for experiments. The blended fuel consisted of 75% pure diesel, 20% bioethanol, and 5% biodiesel fuel and it named DE20. The bioethanol fuel had a purity of 99.9% and was anhydrous. In our previous works [25], [26], [27], [28] using diesel-bioethanol blended fuels, it revealed that 20% bioethanol blending ratio is proper to reduce exhaust emissions with maintaining proper cetane number. In

Numerical models for bioethanol blended diesel fuel spray

In this study, the KIVA-3V release 2 code [31] was used to predict and to analyze the macroscopic spray behavior and the microscopic spray atomization, evaporation characteristics of test fuels. This numerical method generally has been applied for the investigation of fuel spray, combustion and emission characteristics in the cylinder singe the original KIVA code [32] was developed in 1985. In this investigation, the conventional diesel fuel (D100) spray characteristics were calculated by using

Injection characteristics of diesel and diesel-bioethanol blended fuels

Fig. 2 and Fig. 3 show the comparison of the injection characteristics such as the injection quantity and the injection rate between D100 and DE20 fuels. Fig. 2 represented the required energizing duration for the desired injection quantity. As shown in Fig. 2, bioethanol blended diesel fuel need slightly longer energizing duration than a pure diesel fuel. In generally, the injection quantity is proportional to the square root of the product of fuel density and the pressure difference

Conclusions

The combustion and exhaust emission characteristics of diesel and bioethanol-blended diesel fuel were investigated according to spray behavior at the EIC and the CIC in a single cylinder diesel engine. The macroscopic spray behavior characteristics were studied experimentally. In addition, the atomization and evaporation characteristics were studied numerically. Based on the analysis of these spray, atomization, and evaporation characteristics, the combustion and exhaust emissions

Acknowledgement

This work was supported by the Second Brain Korea 21 Project.

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