Heat of Vaporization Measurements for Ethanol Blends Up To 50 Volume Percent in Several Hydrocarbon Blendstocks and Implications for Knock in SI Engines

Abstract

The introduction of more stringent standards for fuel economy as well as greenhouse gas emissions [1] is driving research to increase the efficiency of spark ignition (SI) engines. Approaches for increasing SI engine efficiency include increased compression ratio, direct injection (DI), turbocharging, downsizing, and down-speeding. Higher octane number (more highly knock resistant) fuels allow improved combustion phasing and operation at higher loads at the same engine speed, while also allowing the higher in-cylinder temperature and pressure generated by increased compression ratio and turbocharging which are critical for downsizing and down-speeding [2,3,4]. At the same time, renewable fuel usage is mandated to increase in the United States under the Renewable Fuel Standard [5], and globally under laws enacted in other countries. Ethanol, the most commonly used renewable fuel, has a research octane number (RON) of approximately 110 [6] compared to typical U.S. regular gasoline at 91-93 [2]. Accordingly, high octane number ethanol blends containing from 20 volume percent (vol%) to 40 vol% ethanol are being extensively studied [3,7,8,9,10]. A unique property of ethanol is its high heat of vaporization (HOV), which significantly increases charge cooling for DI engines, providing additional knock resistance.The tendency of a spark-ignited engine fuel to autoignite and cause knock is measured as the octane number, a critical performance parameter for SI engines. In the United States, octane number at the retail pump is given as the anti-knock index, the average of two octane number measurements: research octane number (RON) (ASTM D2699-13b) and motor octane number (MON) (ASTM D2700-13b). The primary differences between the RON and MON measurements are fuel-air charge temperature and engine speed, with the RON test using a comparatively low fuel-air charge temperature (that is dependent on the fuel's latent heat of evaporation) and slower engine speed while the MON test is conducted at a significantly higher fuel-air charge temperature (149°C) and faster engine speed. Recent studies have demonstrated that MON is correlated with different effects in modern engines than was the case when these tests were introduced in 1932, and in fact increasing MON at constant RON may actually lower the fuel knock resistance [11]. The ABSTRACTThe objective of this work was to measure knock resistance metrics for ethanol-hydrocarbon blends with a primary focus on development of methods to measure the heat of vaporization (HOV). Blends of ethanol at 10 to 50 volume percent were prepared with three gasoline blendstocks and a natural gasoline. Performance properties and composition of the blendstocks and blends were measured, including research octane number (RON), motor octane number (MON), net heating value, density, distillation curve, and vapor pressure. RON increases upon blending ethanol but with diminishing returns above about 30 vol%. Above 30% to 40% ethanol the curves flatten and converge at a RON of about 103 to 105, even for...

Effects of iso-octane/ethanol blend ratios on the observance of negative temperature coefficient behavior within the Ignition Quality Tester

“…However, little to no effect as a result of increasing ethanol concentration was observed, as there was no noticeable change in minimum chamber pressure between iso-octane and ethanol with equivalent mass injected. This result is is explained in the work by Chupka et al, [20] which shows that the heat of vaporization differences between ethanol and iso-octane decreases with increase in temperature in the range tested in the IQT.…”

A miniaturized electronic sensor for instant monitoring of ethanol in gasohol fuel blends

“…[8][9][10] It is unusual for an alternative fuel, but ethanol has been reported to potentially enhance the efficiency and performance of internal combustion engines. 11,12 Table 1 shows the physicochemical properties [13][14][15][16][17][18][19][20] of gasoline, ethanol, and gasohol (E10) blended fuel. The lower stoichiometric air to fuel ratio and signicantly higher heat of vaporization of ethanol lead to increased adiabatic charge cooling of the stoichiometric air-E10 mixture.…”

“…Physicochemical properties of typical gasoline, ethanol, and gasohol (E10) fuels relative to internal combustion engines [13][14][15][16][17][18][19][20]. …”

Low-Temperature Combustion of High Octane Fuels in a Gasoline Compression Ignition Engine

“…The LHV of E30 is less than 90% of that of aromatic or alkylate. Suggested by Chupka et al (2015), the heat of vaporization (HoV) of aromatic and alkylate are approximately 350 kJ/kg, which is similar to regular petroleum gasoline. With addition of ethanol, HoV of E30 (highest among fuels) is estimated with nominal value of 550 kJ/kg.…”