Fuel effects in CAI gasoline engines

Effects of the Chemical Structure and Composition of Surrogate Gasoline Fuels on Homogeneous Charge Compression Ignition Combustion in a Single-Cylinder Engine

“…Despite the advantages of using mixture designs to explore the formulation space, their use for the development of fuel formulations for HCCI engines has not been reported. Because several studies suggest that conventional motor gasolines might not perform optimally under HCCI conditions, the present study was focused on finding alternative formulations that improve the performance of HCCI engines. ,− …”

“…Several studies on the influence of the molecular structure on HCCI combustion have reported extreme behaviors between two-stage ignition fuels (e.g., n -heptane), which ignite very easily, and single-stage fuels (e.g., isooctane and toluene), which are difficult to ignite. , In the temperature range relevant to HCCI combustion (900–1200 K), the reactions of H-atom abstraction (), formation (), and internal isomerization () of peroxy radicals are very sensitive to fuel structure A number of studies have examined the effect of fuel type on the performance of HCCI engines. − Diesel fuel, gasoline, and primary reference fuels (PRFs), mixtures of n -heptane and isooctane, have been the fuels most commonly used. From the experience with PRFs, it seems that fuels with some low-temperature heat release are convenient for adequate combustion phasing and power output .…”

“…The possibility of independent control of the ignition delay (combustion phasing) and burning rate by manipulation of the chemical characteristics of fuels might offer additional benefits for HCCI control. However, the main focus has been on the achievement of HCCI combustion with conventional motor gasolines, even though several studies suggest that conventional motor gasolines might not perform optimally under HCCI conditions. ,− It has even been suggested that low-octane fuels, probably below 80 RON, would be beneficial to extend the low-load limit in HCCI engines …”

Experimental Investigation of the Autoignition Behavior of Surrogate Gasoline Fuels in a Constant-Volume Combustion Bomb Apparatus and Its Relevance to HCCI Combustion

“…The understanding of the effects of fuel chemistry on the relationship between ignition delay, burning rate, research octane number (RON), and motor octane number (MON) has been recognized as a critical factor for the development of fuels with improved performance for HCCI engines . Several works have examined the effect of fuel type on the performance of HCCI engines. − From the experience with primary reference fuels (PRF)mixtures of n -heptane and isooctaneit is known that fuels with some low-temperature heat release are convenient for obtaining adequate combustion phasing and power output . However, gasoline composition is much more complex than that of PRFs, and the traditional parameters of fuel performance, such as RON and MON, do not generally correlate with the behavior of gasoline fuels under HCCI conditions. , Thus, there is a need to develop fundamental parameters to describe and predict the performance of hydrocarbon fuels in HCCI engines …”

“…Several approaches have been taken in order to characterize fuel performance in HCCI engines. A major effort in this area has been done by Kalghatgi et al with the development of the concept of octane index (OI), which is calculated from the fuel sensitivity ( S = RON – MON) and engine performance parameters. ,, Kalghatgi et al reported good correlation between the octane index and the crank angle for 50% heat release (CA50) observed in an HCCI engine, but the calculated OIs depend on the engine conditions, which limits the general applicability of this concept. Moreover, the OI does not seem to generally correlate with CA50, even with mixtures of n -heptane and isooctane, as reported by Liu et al Another concept, developed by Ryan et al, is the elevated pressure autoignition temperature (EPAIT), based on ignition delay measurements performed in an Ignition Quality Tester (IQT) at different temperatures. , In this approach, an ignition delay common to all fuels of interest is chosen, and the ignition delay versus temperature data is used to calculate the required temperature for a particular fuel to have the same ignition delay .…”