Elsevier

Atmospheric Environment

Volume 37, Issue 35, November 2003, Pages 4965-4971
Atmospheric Environment

The effect of ethanol blended diesel fuels on emissions from a diesel engine

https://doi.org/10.1016/j.atmosenv.2003.08.029Get rights and content

Abstract

The addition of ethanol to diesel fuel simultaneously decreases cetane number, high heating value, aromatics fractions and kinematic viscosity of ethanol blended diesel fuels and changes distillation temperatures. An additive used to keep the blends homogenous and stable, and an ignition improver, which can enhance cetane number of the blends, have favorable effects on the physicochemical properties related to ignition and combustion of the blends with 10% and 30% ethanol by volume.

The emission characteristics of five fuels were conducted on a diesel engine. At high loads, the blends reduce smoke significantly with a small penalty on CO, acetaldehyde and unburned ethanol emissions compared to diesel fuel. NOx and CO2 emissions of the blends are decreased somewhat. At low loads, the blends have slight effects on smoke reduction due to overall leaner mixture. With the aid of additive and ignition improver, CO, unburned ethanol and acetaldehyde emissions of the blends can be decreased moderately, even total hydrocarbon emissions are less than those of diesel fuel. The results indicate the potential of diesel reformation for clean combustion in diesel engines.

Introduction

Increasing worldwide concern over combustion-related pollutants, such as particulate matter (PM), oxides of nitrogen (NOx), carbon monoxide (CO), total hydrocarbon (THC), acid rain, photochemical smog and depletion of the ozone layer, has led regulatory agencies to implement stringent emission regulations. Diesel engines are one of the major contributors to the pollutant emissions since they are widely used due to high combustion efficiency, reliability, adaptability and cost effectiveness. Soot and NOx are formed during diesel combustion, the required levels of PM, NOx are difficult to achieve through the improvement of combustion chamber and injection design. It is commonly accepted that clean combustion of diesel engines can be fulfilled only if engine development is coupled with diesel fuel reformulation. In the name of energy security, regional air quality, greenhouse gas emission reduction and even economic savings, oxygenated fuels were advocated to reduce particulate emissions (Liotta and Montalvo, 1993; Maricq et al., 1998). The reduction of particulate emissions due to the introduction of oxygenated compounds depends on the molecular structure, oxygen content of the fuel (Miyamoto et al., 1998; Kitamura et al., 2001) and local oxygen concentration in the fuel plume (Donahue and Foster, 2000).

Ethanol is a promising oxygenated fuel. Pure ethanol with additives such as cetane improver can sharply reduce particulates (Bechtold et al., 1991). At the early stage, poor fuel economy and low ignitability were the main barriers to apply ethanol fuel on diesel engines. Since late 1990s, ethanol blended diesel fuel has been used on heavy-duty and light-duty diesel engines in order to modify their emission characteristics. For example, the ethanol–diesel blends with 10% and 15% ethanol could reduce PM emissions by 20–27% and 30–41%, respectively (Spreen, 1999; Kass et al., 2001). The blends containing 83–94% diesel fuel, 5–15% ethanol, 1–3% additive and a small amount of commercially available cetane improver (<0.33% by volume) in the mixture could reduce 41% PM, 27% CO emissions from a heavy-duty diesel engine in laboratory and field tests (Ahmed, 2001). However, ethanol diesel blends increase unburned hydrocarbons (Shih, 1998; Cole et al., 2001), NOx emissions (Cole et al., 2001) and aldehyde emissions (Rideout et al., 1994; Gjirja et al., 1998). Moreover, the viscosity and lubricity of the blends decreases, cetane number linearly reduces at ambient temperature (Caro et al., 2001). Therefore, ignition improver and other additives are required to improve the durability and ignition of diesel engines when ethanol blended diesel fuels are used.

The potential of ethanol to reduce particulate emissions increases the flexibility to control NOx emissions at different engine operating conditions. Higher THC emissions might offer reductant that regenerates NOx adsorbers (Kass et al., 2001). Other environmental benefits associated with ethanol blended diesel fuel include the improvement of biodegradability and the reduction in net emissions of greenhouse gases if ethanol is produced from biomass.

In this study, a solvent additive was prepared to prevent ethanol blended diesel fuels from separating and an ignition improver was added in order to enhance cetane number of the blends. The properties of the blends with/without solvent additive and ignition improver were measured as a function of mixture composition. The effects of ethanol blended diesel fuels on distillation temperature, regulated emissions such as smoke, THC, CO, NOx and unregulated emissions including CO2, acetaldehyde and unburned ethanol were evaluated on a diesel engine.

Section snippets

Equipment

The engine used in this experiment was a four-cylinder direct injection diesel engine with a cylinder bore of 102 mm, a stroke of 120 mm and a compression ratio of 17.5:1. The maximum torque was 245 N m at 1700 rpm and the rated power was 59 kW at 2800 rpm. Tests were carried out only at 1700 rpm. To compare the emissions of various fuels used, the engine was not modified and its start of delivery was kept at 21°crank angle before top dead center.

A Zöllner electric eddy dynamometer was coupled to the

The preparation of ethanol blended diesel fuels

The solubility of ethanol in diesel is affected mainly by temperature, hydrocarbon composition of diesel and water content in the blend (Ecklund et al., 1984). With the increase of ethanol, soluble temperature increases and reaches the maximum when ethanol content is about 50% by volume, then decreases. For example, the blends with 20% ethanol and 50% ethanol will separate at about 0°C and 23°C, respectively (Murayama et al., 1982). However, when ethanol–diesel phase is exposed to small amounts

Conclusions

The addition of ethanol to diesel fuel changes the physicochemical properties of the blends. With the increase of ethanol, density, cetane number, kinematic viscosity, high heat value and aromatics fractions of the blends decrease. Distillation temperatures also change. Additive can enhance the stability of ethanol blended diesel fuel, and partly restore their viscosity. Ignition improver is needed to enhance their cetane number.

The impacts of ethanol on emissions vary with engine operating

Acknowledgements

This study was financially supported by Hi-Tech Research and Development Program of China in the program of “Integration and Optimization of NOx Reduction Catalysts and Diesel Engines” under contract 2001AA64304003, and by Tsinghua University in the program of “New Concept Design Based on Oxygenated Bio-fuel for Automobiles” under contract Jz2002002.

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