Evaluation of Dimethyl Carbonate as Alternative Biofuel. Performance and Smoke Emissions of a Diesel Engine Fueled with Diesel/Dimethyl Carbonate/Straight Vegetable Oil Triple Blends

Abstract

Dimethyl carbonate (DMC) is an interesting blending component for diesel fuel (D) owing to the high oxygen content (53 wt.%) and the absence of C–C bonds in its structure. Moreover, DMC can be produced from CO2 and methanol, which provides a renewable way to reduce anthropogenic CO2. This research has been addressed to assess the use of DMC as a solvent of sunflower oil (SO) and castor oil (CO), with the purpose of obtaining biofuels that can replace fossil diesel as much as possible. The blending of DMC with straight vegetable oils (SVOs) reduces their high viscosity, allowing their usage as drop-in biofuels without chemical treatments. Based on viscosity requirements of European Standard EN 590, the optimal DMC/SVO double blends have been tested as direct biofuels by themselves or mixed with fossil diesel in D/DMC/SVO triple blends. Relevant physico-chemical properties of fuels have been analyzed. Engine parameters such as power output, brake-specific fuel consumption (BSFC) and soot emissions have been studied to determine the effect of new biofuels on efficiency of a diesel engine. An outstanding engine efficiency is shown by the studied D/DMC/SVO triple blends, either with SO or CO as an SVO. The low calorific value of DMC is the main reason for reduction in power and BSFC, as the amount of diesel in the triple blends is reduced. Experimental results demonstrate that the use of these biofuels allows the replacement of up to 40% of fossil diesel, without compromising the power and BSFC of the engine, and accomplishing optimal cold flow properties and a marked drop in exhaust emissions.

Advanced Biofuels from ABE (Acetone/Butanol/Ethanol) and Vegetable Oils (Castor or Sunflower Oil) for Using in Triple Blends with Diesel: Evaluation on a Diesel Engine

“…This would be a consequence of the higher energy density of the fuels composed of sunflower oil, which improves the power output of the engine. Also, the lower cetane number of the castor oil blends prolongs the ignition delay, contributing to a higher amount of fuel burned in the premixed combustion phase [34]. In this sense, the results obtained here are consistent with those reported in recent studies [51,55].…”

“…Lee et al observed similar behavior with the addition of 10 and 20% ABE to diesel [53]. This is explained by the high oxygen content in the biofuels, which promotes the oxidation of C, resulting in a better combustion process [29,[32][33][34][35]. Moreover, the low cetane number in the blends, as well as the higher volatility of ABE in comparison to diesel, promote a higher proportion of fuel burning in the premixed combustion phase, which increases the oxidation of the soot particles [53].…”

“…In this equation, C is the calibration constant of the measurement system, specified by the manufacturer (0.037150 (mm 2 /s)/s 40 • C), following the methodology described in previous works [29,34]. The viscosity values reported here are the average of the three determinations, following the standard ASTM (American Society for Testing and Materials) D2270-79 method for calculating the viscosity index from kinematic viscosity at 40 Cold flow properties are responsible for the solidification of the fuel under cold operating conditions.…”

“…Energy performance and exhaust emissions were analyzed following the previously described experimental methodology [29,[32][33][34] on a 4-stroke and single-cylinder engine (dimensions: 78 mm bore and 67 mm stroke), with a forced air-cooling system by flywheel fan. The main specifications of the engine are shown in Table 1.…”

“…However, the incorporation of DEE in a triple blend with a SVO (diesel/vegetable oil/DEE) allows for a substitution with fossil diesel of up to 40% by volume, not only promoting good results in terms of engine power and emission reductions, but also leading to an improvement in the cold flow behavior of fuel [30]. Many other solvents have also been employed as an LVLC in triple blends with diesel and oil, such as ethyl acetate (EA) [31,32], diethyl carbonate [33], dimethyl carbonate [34], and acetone [35]. In general, a fossil diesel substitution above 40% was obtained, attaining a reduction in pollutant emissions without diminishing the power generated by the engine.…”