Ethanol-Diesel Blends

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Abstract: Blends of up to 15% of ethanol in diesel fuel, known as e-diesel, can be used in compression ignition engines. E-Diesel can produce certain reductions in regulated diesel emissions, especially those of diesel particulate matter. Disadvantages of e-diesel include low flash point, which may present a safety issue.

Introduction

Numerous techniques have been evaluated to allow for the concurrent use of diesel and ethanol in compression ignition engines. Some of these techniques include alcohol fumigation, dual injection, alcohol-diesel fuel emulsions, and alcohol-diesel fuel blends. Among these approaches, only alcohol-diesel emulsions and blends are compatible with most commercial diesel engines. Since emulsions are difficult to achieve and tend to be unstable, blends—either as micro-emulsions or using co-solvents—are the most common approach as they are stable and can be used in engines with relatively no modifications.

Blends of ethanol with diesel fuel are often referred to as “E-Diesel” or “eDiesel”. Sometimes, ethanol-diesel blends are also called “oxygenated diesel”—a term that is not particularly precise, as diesel blends containing methyl ester biodiesel or any other additive that includes oxygen can be also described as oxygenated diesel.

In e-diesel blends, standard diesel fuel (such as US No. 2) is typically blended with up to 15% (by volume) of ethanol using an additive package that helps maintain blend stability and other properties—most importantly cetane number and lubricity. The additive package may comprise from 0.2% to 5.0% of the blend. There is currently no specification for e-diesel in the USA.

The use of e-diesel can bring some reductions in diesel PM emissions, while contradictory reports exist on its effect on NOx, CO, and HC emissions. Perhaps the biggest advantage of e-diesel is its partially renewable character, if renewable ethanol is used as the blending stock. Considering its potentially significant operational and safety issues—the latter including very low flash point—e-diesel will likely remain a niche market fuel of limited applicability.

Ethanol fumigation into the engine intake port is an alternative way to use ethanol in the diesel engine. As this method requires modifications to the engine, its application remains even more limited. Aftermarket dual fuel kits have been developed that allow port fuel injection of ethanol. Some kits also incorporate a heat exchanger to preheat the ethanol to a temperature of 50-80°C to improve fuel vaporization in the intake port. In one study [3339], hydrous ethanol (90% by vol.) was fumigated into the intake port of a John Deere 4045 HF475 Tier 2 diesel engine. The engine was operated with ethanol substitution rates up to 37%, based on the fumigant energy fraction (FEF), but the effect on emissions was marginal. As FEF increased, NO emissions decreased, but the NO reduction was balanced by an increase in NO₂ emissions. Emissions of CO, THC, and ethanol all increased with the FEF, while soot emissions generally decreased.