Effects of refinery stream gasoline property variation on the auto-ignition quality of a fuel and homogeneous charge compression ignition combustion

Abstract

The combination of in-cylinder thermal environment and fuel ignition properties plays a critical role in the homogeneous charge compression ignition engine combustion process. The properties of fuels available in the automotive market vary considerably and display different auto-ignition behaviors for the same intake charge conditions. Thus, in order for homogeneous charge compression ignition (HCCI) technology to become practically viable, it is necessary to characterize the impact of differences in fuel properties as a source of ignition/combustion variability. To quantify the differences, 15 gasolines composed of blends made from refinery streams were investigated in a single-cylinder homogeneous charge compression ignition engine. The properties of the refinery stream blends were varied according to research octane number, sensitivity (S = research octane number 2 motor octane number) and volumetric contents of aromatics and olefins. Nine fuels contained 10% ethanol by volume, and six more were blended with 20% ethanol. Pure ethanol (E100) and an un-oxygenated baseline fuel (RD3-87) were included too. For each fuel, a sweep of intake temperature at a consistent load and engine speed was conducted, and the combustion phasing given by the crank angle of 50% mass fraction burned was tracked to assess the sensitivity of auto-ignition to fuel chemical kinetics. The experimental results provided a wealth of information for predicting the HCCI combustion phasing from the given properties of a fuel. In this study, the original octane index correlation proposed by Kalghatgi based solely on fuel research octane number and motor octane number was found to be insufficient for characterizing homogeneous charge compression ignition combustion of refinery stream fuels. A new correlation was developed for estimation of auto-ignition properties of practical fuels in the typical HCCI engine. Fuel composition, captured by terms indicating the fraction of aromatics, olefins, saturates and ethanol, was added to generate the following formula: OI JKZ = RONÀ K 0 Á S + k Á (Aromatics 2 )(Olefins + Saturates) + eÁ (Aromatics Á Ethanol). The results indicate a significantly improved estimation of combustion phasing for gasoline fuels of varying chemical composition under low-temperature combustion conditions. Quantitative findings of this investigation and the new octane index correlation can be used for designing robust HCCI control strategies, capable of handling the wide spectrum of fuel chemical compositions found in pump gasoline.

Insights into Engine Knock: Comparison of Knock Metrics across Ranges of Intake Temperature and Pressure in the CFR Engine

“…Due to ongoing development in the engine and fuel arena, it is therefore of little surprise that the RON and MON method no longer encapsulate the operating regime of modern engines [10,11,12], and this has motivated the development and utilization of other fuel ratings, such as the octane index, which was formulated by Kalghatgi as a practical means to correlate RON and MON to Knock Limited Spark Advance (KLSA) in modern engines [11,13,14]. Iterations of the octane knock index have also been applied to predict the performance of gasoline-type fuels in compression ignition engines [15,16,17,18,14], where the onset of auto-ignition arguably plays an even greater role than in SI engines in operational characteristics. It is interesting to note that various improvements to the octane rating system, such as including weighting factors for fuel composition, as done by Lacey et al [18], were reportedly considered in the 1960's [9].…”

“…Iterations of the octane knock index have also been applied to predict the performance of gasoline-type fuels in compression ignition engines [15,16,17,18,14], where the onset of auto-ignition arguably plays an even greater role than in SI engines in operational characteristics. It is interesting to note that various improvements to the octane rating system, such as including weighting factors for fuel composition, as done by Lacey et al [18], were reportedly considered in the 1960's [9].…”

Screening Method for Fuels in Homogeneous Charge Compression Ignition Engines: Application to Valeric Biofuels

“…A modified OI model was proposed to include nonlinear terms, capturing the effect of main chemical constituents. 17 Additional test facilities could also complement the enginetype results. Perez and Boehman have shown that the use of an ignition quality tester (IQT) could provide better information on the timing of ignition in HCCI than correlations based on MON and RON.…”

Effect of spray impingement distance on piston top fuel adhesion in direct injection gasoline engines

“…Eventually, one point with h(x, y) and DI(x, y) was obtained. By varying the mixture volume from 0.1 to 10 mL, the calibration curve was acquired by equation (2). The calibration curves for 28 and 40 mm are plotted in Figure 5.…”

“…This is due to the better air and mixture control by DI compared to port fuel injection. [1][2][3] However, the impingement of liquid fuel on the wall of the combustion chamber and piston is a major drawback of this technique, because wall wetting leads to pool fires linked with rich diffusion flames on the top of the liquid deposit. 4,5 This can contribute to unwanted pollutant formation and an increase in unburned hydrocarbons.…”