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Occurrence of sporadic super-knock is the main obstacle to the development of advanced gasoline engines. One of the possible inducements of super-knock, agglomerated soot particle induced pre-ignition, was studied for high boosted gasoline direct injection (GDI) engines. The correlation between soot emissions and super-knock frequency was investigated in a four-cylinder gasoline direct injection production engine. The test results indicate that higher in-cylinder soot emission correlate with more pre-ignition and super-knock cycles in a GDI production engine. To study the soot/carbon particles trigger super-knock, a single-cylinder research engine for super-knock study was developed. The carbon particles with different temperatures and sizes were introduced into the combustion chamber to trigger pre-ignition and super-knock.

n-butanol has been recognized as a promising alternative fuel for gasoline and may potentially overcome the drawbacks of methanol and ethanol, e.g. higher energy density. In this paper, the spray characteristics of gasoline and n-butanol have been investigated using a high pressure direct injection injector. High speed imaging and Phase Doppler Particle Analyzer (PDPA) techniques were used to study the spray penetration and the droplet atomization process. The tests were carried out in a high pressure constant volume vessel over a range of injection pressure from 60 to 150 bar and ambient pressure from 1 to 5 bar. The results show that gasoline has a longer penetration length than that of n-butanol in most test conditions due to the relatively small density and viscosity of gasoline; n-butanol has larger SMD due to its higher viscosity. The increase in ambient pressure leads to the reduction in SMD by 42% for gasoline and by 37% for n-butanol.

Using EGR instead of throttle to control the load of a stoichiometric dual-fuel dieseline (diesel and gasoline) compression ignition (SDCI) engine with three-way catalyst (TWC) aftertreatment is considered a promising technology to address the challenges of fuel consumption and emissions in future internal combustion engines. High-speed imaging is used to record the flame signal in a single-cylinder optical engine with a PFI+DI dual injection system. The premixed blue flame is identified and separated using green and blue channels in RGB images. The effects of injection timing on SDCI combustion are studied. An earlier injection strategy is found to be ideal for soot reduction; however, the ignition-injection decoupling problem results in difficulties in combustion control. It is also found that a split injection strategy has advantages in soot reduction and thermal efficiency.

High boost and direct injection hold the potential of enhanced power density and fuel consumption in the development of gasoline engines. However, super-knock with strong destructiveness was widely reported at low-speed and high-load operating regime in turbocharged GDI engines. The objective of this study is to clarify the characteristics of super-knock and to try to find some feasible solutions to suppress super-knock. To fast evaluate super-knock at low-speed and high-load regime, a rapid test procedure including three super-knock test sections of 5000 cycles with 3 idle operations, was proposed. The experimental data indicate that pre-ignition is not the sufficient condition for super-knock. Pre-ignition may lead to super-knock, heavy knock, slight knock, and non-knock. Compared with conventional knock, knock intensity of super-knock is much higher and the maximum amplitude of pressure rise at start of knock is more than one order of magnitude higher.

Homogeneous Charge Compression Ignition (HCCI) and Spark Ignition (SI) dual-mode operation provides a practical solution to apply HCCI combustion in gasoline engines. However, the different requirements of air-fuel ratio and EGR ratio between HCCI combustion and SI combustion results in enormous control challenges in HCCI/SI mode switch. In this paper, HCCI combustion was achieved in a four-cylinder gasoline direct injection engine without knock and misfire using close-loop control by knock index. Assisted Spark Stratified Compression Ignition (ASSCI) combustion was obtained stably at medium-high load. ASSCI combustion exhibits two-stage heat release with initial flame propagation and controlled auto-ignition. The knock index of ASSCI combustion is less than HCCI combustion due to the lower pressure rise rate.