High concentration ethanol require special engines. Ethanol use in spark-ignited engines is relative easy, since the properties of ethanol resemble gasoline. FFV spark-ignition cars for high-oxygen content fuels, for example E85, are well-known and widely on market. Instead, ethanol use in the compression ignition engines is challenging. If ethanol is to be used in compression ignition engines, either the engine or the fuel has to be modified, the latter option requiring fuel additives. Ethanol differs significantly from conventional diesel fuel regarding cetane number, heating value, self-ignition temperature, vaporization characteristics, and boiling point. Cetane number of neat ethanol is less than 12, whereas today the requirement for diesel in Europe is higher than or equal to 51 (properties of ethanol). Thus neat ethanol as such will not ignite in conventional diesel engine. Also the lubricity of ethanol is unacceptable for high-pressure injection pumps in diesel engines. The low boiling point of ethanol increases the risk of cavitation, and the high conductivity the risk of corrosion (IEA-AMF Task 46 Nylund et al. 2015, Peckham 2001, McCormick 2001). In the past Detroit Diesel manufactured glow-plug equipped heavy-duty engines for using methanol or ethanol. However, many problems like engine wear, and glow-plug failures and excessive fuel consumption were encountered. Thus the production of these engines was discontinued. In Sweden another approach was selected: adding ignition improver and lubricity additive to ethanol to enable the usage of the diesel combustion process (Diesel engines for additized ethanol; Scania’s ethanol engine).

TThe following special engine technologies for alcohol use are commonly considered:

• Flexible Fuel Vehicle (FFV) cars / E85 (fuel containing up to 85% ethanol in gasoline) - FFV spark-ignition cars are well-known commercial technology. The modifications needed in engines and fuel infrastucture are relatively small. In addition, some changes are also needed to infrastructure. Several IEA-AMF Tasks have studied "FFV/E85 concept".
• Diesel engines for additized ethanol (ED95) - Scania's ethanol engines for cetane improver additized fuel (Etamax D) are commercially available technology for using ethanol in heavy-duty diesel engine. IEA-AMF Task 46 studied this concept.
• Dual fuel engines - Dual injection, or pilot injection, is a combination of two individual fuel systems with the direct injection into the combustion chamber. By using a pilot injection of diesel to help to ignite a later injection of neat ethanol. Up to 90% ethanol can be used at high loads and 50-60 % at low and medium loads. A range of ethanol percentages can be used, as well as neat diesel. This technology creates opportunities for controlling the combustion to a very high degree, for example, more effectively aiming at the highest efficiency or the lowest NO_x and PM emissions. This technique is a variant of what is called partial premixed controlled combustion (PCCI). Lubrication additives and/or improved materials might be needed for this technique. The main advantages are high engine efficiencies, high displacement of fossil diesel, and low NO_x and PM emissions. (Larsen 2009).
• Fumigation - One option is to vaporize and mix ethanol with intake air, this is called fumigation. At medium loads up to 50-60 % ethanol can be fumigated, whereas at low and high loads ethanol is limitedly supplied. Use of fumigation in turbocharged diesel engines has been shown to be problematic. Advantages of this technique are in some cases increased engine efficiency, relatively large replacement of diesel fuel, relatively easy retrofitting of the system, and the fact that the engine is flexible enough to run on regular diesel if needed. (Larsen 2009).
• Other options - Ignition of the ethanol can also be secured by a spark-plug, a glow-plug or by hot recirculated exhaust gases. New or combined combustion systems may offer possibilities, as well. (Petterson 1994). One idea could be to produce small amounts of hydrogen on-board, and use this as an ignition enhancer. The desired effect could be achieved possibly by introducing the hydrogen mix into the intake manifold late during the intake stroke. Ethanol gives inherently low particulate emissions, but there is probably going to be a need for NO_x control by EGR, lean NO_x or NO_x storage catalyst or perhaps SCR, and a control of unburned fuel and aldehydes by oxidation catalyst (Nylund 2004b, Larsen 2009).

References

Larsen, U., Johansen, T. and Schramm, J. (2009) Ethanol as a fuel for road transportation. IEA Advanced Motor Fuels Agreement. Task 35. http://www.iea-amf.org/app/webroot/files/file/Annex%20Reports/AMF_Annex_35-1.pdf

McCormick, R.L. and Parish, R. (2001) Technical Barriers to the Use of Ethanol in Diesel Fuel. National Renewable Energy Laboratory. Colorado 2001 (report NREL/MP-540-32674).

Nylund, Nils-olof, Timo Murtonen, Mårten Westerholm, Christer Söderström, Timo Huhtisaari, and Gurpreet Singh (2015) “Testing of Various Fuel and Additive Options in a Compression-Ignited Heavy-Duty Alcohol Engine.” In The 21st International Symposium on Alcohol Fuels, 10 March 2015 , Gwangju, Korea., 1–15. IEA-AMF Task 46.

Peckham, J. (editorial) (2001) Ethanol-diesel raises safety, performance, health concerns: Autos. Diesel Fuel News, 12 November 2001 (11/2001). p. 9–10.

Petterson, L. (1994) Alcohol Fuels for Internal Combustion Engines. Dissertation. Kungliga Tekniska Högskolan. Stockholm, Sweden.