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This study explores the use of two conventional ignition improvers, 2-ethylhexyl nitrate (EHN) and di-tert-butyl peroxide (DTBP), to enhance the autoignition of the regular gasoline in an homogeneous charge compression ignition (HCCI) engine at naturally aspirated and moderately boosted conditions (up to 180 kPa absolute) with a constant engine speed of 1200 rpm. The results showed that both EHN and DTBP are very effective for reducing the intake temperature (Tin) required for autoignition and for enhancing stability to allow a higher charge-mass fuel/air equivalence ratio (ϕm). On the other hand, the addition of these additives can also make the gasoline too reactive at some conditions, so significant exhaust gas recirculation (EGR) is required at these conditions to maintain the desired combustion phasing. Thus, there is a trade-off between improving stability and reducing the oxygen available for combustion when using ignition improvers to extend the high-load limit.

Factors affecting the pressure rise rate, and consequently the high-load limit, in the sequential ignition of a homogeneous charge in a temperature gradient have been identified. The pressure rise rate decreases with an increase in the magnitude of the temperature gradient and an increase in the sensitivity of the constant volume ignition delay time to temperature. It increases with an increase in the intrinsic reaction rate (i.e., the reaction rate for a charge of uniform composition and temperature). Since the ignition delay time and the intrinsic reaction rate are directly related to fuel properties, the high-load limit is sensitive to fuel selection. The above three factors are used to explain the high-load limit obtained from a knock limited Controlled Auto-Ignition (CAI) engine with a homogeneous charge operating with three different fuels. The fuel comparisons are made with the engine operating at the same combustion phasing.

Partially premixed combustion (PPC) is intended to improve fuel efficiency and minimize the engine-out emissions. PPC is known to have the potential to reduce emissions of nitrogen oxides (NOx) and soot, but often at the expense of increased emissions of unburned hydrocarbons (HC) and carbon monoxide (CO). PPC has demonstrated remarkable fuel flexibility and can be operated with a large variety of liquid fuels, ranging from low-octane, high-cetane diesel fuels to high-octane gasolines and alcohols. Several research groups have demonstrated that naphtha fuels provide a beneficial compromise between functional load range and low emissions. To increase the understanding of the influence of individual fuel components typically found in commercial fuels, such as alkenes, aromatics and alcohols, a systematic experimental study of 15 surrogate fuel mixtures of n-heptane, isooctane, toluene and ethanol was performed in a light-duty PPC engine using a design of experiment methodology.

Homogeneous charge compression ignition (HCCI) combustion with fully premixed charge is severely limited at high-load operation due to the rapid pressure-rise rates (PRR) which can lead to engine knock and potential engine damage. Recent studies have shown that two-stage ignition fuels possess a significant potential to reduce the combustion heat release rate, thus enabling higher load without knock. This study focuses on three factors, engine speed, intake temperature, and fuel composition, that can affect the pre-ignition processes of two-stage fuels and consequently affect their performance with partial fuel stratification. A model fuel consisting of 73 vol.% isooctane and 27 vol.% of n-heptane (PRF73), which was previously compared against neat isooctane to demonstrate the superior performance of two-stage fuels over single-stage fuels with partial fuel stratification, was first used to study the effects of engine speed and intake temperature.

Effects of six different fuels on low temperature premixed compression ignition (PCI) combustion were experimentally investigated in this paper with a light-duty HSDI engine. The PCI combustion concept reduces NOx and smoke emissions simultaneously by low temperature and premixed combustion, respectively. To achieve low temperature and premixed combustion, the ignition delay is prolonged and the injection duration is shortened. Six fuels were chosen to examine the influence of cetane number (CN) and other fuel properties on low temperature PCI combustion. The fuel selection also included a pure Gas- to-Liquid (GTL) fuel and a blend of base diesel and 20% soy based biodiesel (B20). Fuel effects were studied over a matrix of seven part load points in the low temperature combustion mode. The seven part load points were specified by engine speed (RPM) and brake mean effective pressure (BMEP).

Six diesel, kerosene, gasoline-like, and naphtha fuels have been tested in a single cylinder diesel engine and a demonstrator vehicle, both equipped with similar engine technology and optimized for advanced combustion performance. This study was completed in order to investigate the potential to reduce engine-out emissions while maintaining engine efficiency and noise levels through changes in both engine hardware and fuel properties. The fuels investigated in this study were selected in order to better understand the effects of ignition quality, volatility, and molecular composition on engine-out emissions and performance. The optimized bench engine used in this study included engine hardware enhancements that are likely to be used to meet Euro 6 emissions limits and beyond, in part by operating under advanced combustion conditions, at least under some speed and load conditions.