Alcohols in special engines
Usage of high concentration alcohols require special engines. Ethanol use in the compression ignition engines is especially challenging, since the properties of ethanol resemble gasoline, not diesel fuel. If ethanol or methanol is to be used in compression ignition engines, either the engine or the fuel has to be modified, the latter option requiring fuel additives. The following options of special engines for alcohols are the most common technologies.
- Flexible Fuel Vehicle (FFV) cars / E85 (commercial) - FFV spark-ignition cars for high-oxygen content fuels, for example E85, are well-known commercial technology. The modifications needed in engines are relatively small. In addition, some changes are also needed to infrastructure. In Brazil, FFV cars are designed also for use of hydrous E100 fuel. In China, 85% methanol M85 is used in FFV cars.
- Diesel engines for additized ethanol “Etamax D concept”- Scania's ethanol engines for cetane improver additized fuel (Etamax D) are commercially available technology for using ethanol in heavy-duty diesel engine. The need for an ignition improver additive significantly increases the cost of running heavy-duty vehicles on ethanol fuels.
- 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 NOx 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 NOx 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 NOx control by EGR, lean NOx or NOx storage catalyst or perhaps SCR, and a control of unburned fuel and aldehydes by oxidation catalyst (Nylund 2004b, Larsen 2009).
Larsen, U., Johansen, T. and Schramm, J. (2009) Ethanol as a fuel for road transportation. IEA Advanced Motor Fuels Agreement. Annex XXXV. http://www.iea-amf.org/app/webroot/files/file/Annex%20Reports/AMF_Annex_35-1.pdf
Petterson, L. (1994) Alcohol Fuels for Internal Combustion Engines. Dissertation. Kungliga Tekniska Högskolan. Stockholm, Sweden.