Study finds adding DME to ethanol/diesel emulsion improves performance and lowers fuel consumption and emissions over emulsion or base diesel
|Comparing fuel consumption with diesel, 50D/50E and 50D/50E + 7% DME. Credit: ACS, Ashok 2011. Click to enlarge.|
In a study published in the ACS journal Energy & Fuels, M. P. Ashok of Annamalai University, Tamil Nadu, India reports that adding dimethyl ether to an ethanol/diesel emulsion results in an increase in brake thermal efficiency and a decrease in specific fuel consumption (SFC), particulate matter, smoke density, and oxides of nitrogen compared to either the emulsion or a base diesel fuel.
Emulsification of diesel with ethanol is one of the possible approaches to improve fuel economy and reduce emissions of pollutants from diesel engines. However, Ashok noted, ethanol addition to diesel results in different physicochemical changes in diesel fuel properties, particularly a reduction in cetane number, viscosity, and heating value. Ashok started the project by first examining the performance of different ethanol/diesel blends: 90D/10E, 80D/20E, 70D/30E, 60D/40E, and 50D/50E, all prepared on the basis of the water-in-oil (W/O)-type emulsion method.
Ashok selected the 50D/50E ratio as the best of the emulsified blends due to its increase in brake thermal efficiency and decrease in specific fuel consumption, smoke density (SD) and PM.
Even though this emulsified fuel gives better brake thermal efficiency and gives less SFC, SD, and PM based on the performance and emissions, respectively, in comparison to diesel no. 2, there is a significant increase in NOx emission over diesel no. 2. This is due to the lower cetane number of ethanol, which causes high temperatures, resulting in a longer ignition delay...This emission of NOx can be controlled by adding a suitable additive, which must have the property of a high cetane number. This leads to a reduction of the temperature, resulting in a smaller ignition delay, thus reducing emission of NOx.
Hence, for this present work, dimethyl ether (DME) has been selected as an additive, because of its high cetane number, noncorrosiveness, and low volatility.—Ashok 2011
Ashok added DME on a 7% by volume basis with the selected emulsified fuel ratio of 50D/50E and carried out performance, emission, and combustion tests, along with performance and emission tests with diesel no. 2 and emulsified fuel 50D/50E.
Testing was done in a one-cylinder, four-stroke 5.2 kW engine with a compression ratio of 17.5:1. Speed was constant 1500 rpm, injection timing was 23 ° before TDC, and injection pressure was 220 kgf/cm2 (215 bar).
|Click to enlarge. Credit: ACS, Ashok 2011.|
Among his results were:
Brake thermal efficiency increases from 35.6% (emulsified fuel) to 38.1% (DME-added emulsified fuel).
There is a difference in SFC of 0.05 kg/kWh between DME-added emulsified fuel and the emulsified fuel.
The best decrease in the SD value is obtained for DME-added emulsified fuel compared to the other two fuels. The value for DME-added emulsified fuel and the emulsified fuels are 9.8 and 14.9 HSU, respectively.
PM emission is low at lower outputs and equal to the emulsified fuel values at higher outputs for DME-added emulsified fuel.
The NOx value is reduced because of the additive DME;it is usually higher for the emulsified fuel using the normal surfactant. NOx was reduced from 3.68 to 2.856 g/kWh for 50D/50E emulsified fuel and DME-added emulsified fuel, respectively.
Ignition delay is decreased for DME-added emulsified fuel compared to the other two fuels. At lower output, the difference in value is 4.9° crank angle (CA).
The peak pressure and the maximum rate of pressure rise decrease because of the reduction in ignition delay.
The heat release rate is higher for the emulsified fuel than the diesel and additive DME-added emulsified fuels. The maximum value obtained by the emulsified fuel is 106.591 kJ m-3 deg-1, and the minimum value attained by the additive DME-added emulsified fuel is 53.81 kJ m-3 deg-1.
M. P. Ashok (2011) Effect of Dimethyl Ether in a Selected Ethanol/Diesel Emulsified Fuel Ratio and Comparing the Performance and Emission of the Same to Diesel Fuel. Energy & Fuels Article ASAP doi: 10.1021/ef2007547 |