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Homogeneous Charge Induced Ignition (HCII) combustion is believed to be a promising approach to achieve clean and high efficiency combustion. HCII can be realized by using port-injection of the high-volatile fuel (gasoline) to prepare in-cylinder homogeneous charge and direct injection of the high-ignitable fuel (diesel) near the top dead center to control the start of combustion. In the current study, a numerical study was carried out to understand the mixing and auto-ignition process in HCII combustion. A multicomponent chemical kinetic mechanism for gasoline and diesel, consisting of n-heptane, iso-octane, ethanol, toluene, diisobutylene and n-decane, has been developed for predicting their ignition and oxidation. The final mechanism consists of 104 species and 398 reactions. This mechanism was validated with the experimental data of ignition delay times and laminar flame speeds for each component and real transportation fuels.

This research focuses on the potential of Homogeneous Charge Induced Ignition (HCII) combustion meeting the Euro V emission standard on a heavy-duty multi-cylinder engine using a simple after-treatment system. However, in our previous studies, it was found that the gasoline ratio was limited in HCII by the over-high compression ratio (CR). In this paper, the effects of reducing CR on the performances of HCII at medium and high loads were explored by experimental methods. It was found that by reducing CR from 18:1 to 16:1 the peak in-cylinder pressure and the peak pressure rise rate were effectively reduced and the gasoline ratio range could be obviously extended. Thus, the combustion and emission characteristics of HCII at medium and high loads were noticeably improved. Soot emissions can be significantly reduced because of the increase of premixed combustion ratio. The reduction could be over 50% especially at high load and high speed conditions.

Wide Distillation Fuel (WDF), with a distillation range from Initial Boiling Point of gasoline to Final Boiling Point of diesel, can be easily gained directly by blending diesel with gasoline. However, the reduced auto-ignitability of WDF could lead to higher HC emissions. Polyoxymethylene Dimethyl Ethers (PODE), with good volatility and oxygen content of up to 49%, have great potential to improve combustion and emission characteristics, especially for soot reduction. Experiments were carried out in a light-duty four-cylinder diesel engine fueled with neat diesel, gasoline/diesel blends (GD), GD/PODE blends (GDP) and the combustion and emission characteristics were carefully examined. Results showed that GDP had the lowest PM emission and diesel had the poorest one among the three fuels. Due to the addition of gasoline and the relatively poor ignitability, GD had lower combustion efficiency and higher Soluble Organic Fraction (SOF) emissions than diesel.

A new combustion mode namely multiple premixed compression ignition (MPCI) for gasoline engines was proposed. The MPCI mode can be realized by two or more times gasoline injections into cylinder with a high pressure around the compression TDC and featured with a premixed combustion after each injection in the cylinder, which is different from the existed gasoline direct injection compression ignition (GDICI) modes such as homogeneous charge compression ignition (HCCI) mode with gasoline injection occurred in intake stroke, and partially premixed compression ignition (PPCI) mode with multiple gasoline injections in intake and compression strokes before the start of combustion (SOC). Therefore the spray and combustion of the MPCI mode are alternatively occurred as "spray-combustion-spray-combustion" near the TDC, rather than "spray-spray-combustion" sequence as traditional PPCI gasoline engines.

Gasoline engines suffer low thermal efficiency and diesel engines have the emission problem of the trade-off between NOx and soot emissions. Homogeneous Charge Induced Ignition (HCII) is introduced using a port injection of gasoline to form a homogeneous charge and using a direct injection of diesel fuel to ignite. HCII has the potential to achieve high thermal efficiency and low emission combustion. However, HCII combustion mode still has problems of high THC emissions at low load and high pressure rise rate at high load. In order to improve the gasoline reactivity and reduce THC emissions, double injection of diesel was applied in HCII mode. In order to reduce peak pressure rise rate (PPRR), a two-staged high-temperature heat release is achieved at suitable engine condition. The effects of HCII mode on combustion and emission characteristics are studied in a light-duty engine.

This study uses Fourier analysis to investigate the relationship between the heat release event and the frequency composition of pressure oscillations in a variety of combustion modes. While kinetically-controlled combustion strategies such as HCCI and RCCI offer advantages over CDC in terms of efficiency and NOX emissions, their operational range is limited by audible knock and the possibility of engine damage stemming from high pressure rise rates and oscillations. Several criteria such as peak pressure rise rate, ringing intensity, and various knock indices have been developed to quantify these effects, but they fail to capture all of the dynamics required to form direct comparisons between different engines or combustion strategies. Experiments were performed with RCCI, HCCI, and CDC on a 2.44 L heavy-duty engine at 1300 RPM, generating a significant diversity of heat release profiles.

Two premixed compression ignition modes for low octane gasoline are numerically investigated. The multiple premixed compression ignition (MPCI) mode is featured with a sequence of “spray- combustion- spray- combustion”, while the partially premixed compression ignition (PPCI) mode is a sequence of “spray- spray- combustion”. This paper compares the combustion process of the two modes using multi-dimensional CFD code, KIVA-3v, which can perform chemical reaction calculations for different fuels by a discrete multiple component (DMC) method. The fuel used for simulation consists of 58.5% i-C8H18 and 41.5% n-C7H16 in volume, and has the same RON and similar physical properties to straight-run naphtha used in the experiment. The engine operating condition is fixed at a 1600rpm and 0.7 MPa IMEP. The injection strategies for these two modes are different. All of the parameters in the simulation come from the single cylinder engine experiments.

The detailed chemical kinetics was implemented into the 0D single-zone model, 1D engine cycle model and 3D CFD model respectively. Both simulation and experiment were carried out on a four-stroke gasoline HCCI engine with direct injection. The 0D model (HRG) was developed to study the isolating effect of HCCI parameters. The 1D engine cycle model with HRG was established to study the gas exchange process and the direct injection strategy in the gasoline HCCI engine with two-stage direct injection (TSDI) and negative valve overlap (NVO). The 3D model with HRG was constructed to study the ignition control mechanism in “two-zone HCCI” combustion via analysis the auto-ignition spots distribution in combustion chamber. “Two-zone HCCI” is defined in this paper as premixed ultra-lean compression ignition combining with premixed ultra-rich compression ignition. The three models were validated by experiments.

In this research, propane flash boiling sprays discharged from a five-hole gasoline direct injector were studied in a constant volume vessel. The fuel temperature (Tfuel) ranged from 30 °C to 90 °C, and the ambient pressure (Pamb) varied from 0.05 bar to 11.0 bar. Different flash boiling spray behavior compared to that under sub-atmospheric conditions was found at high Pamb. Specifically, at the sub-atmospheric pressures, the individual flashing jets merged into one single jet due to the strong spray collapse. In contrast, at Pamb above 3.0 bar and Tfuel above 50 °C, the spray collapse was mitigated and the flashing jets were separated from each other. Further analyses revealed that the mitigation of spray collapse at high Pamb was ascribed to the suppression of jet expansion. In addition, it was found that the spray structure was much different at similar Rp, indicating that Rp lacked the generality in describing the structure of flash boiling sprays.

HCCI combustion was studied in a 4-stroke gasoline engine with a direct injection system. The electronically controlled two-stage gasoline injection and spark ignition system were adopted to control the mixture formation, ignition timing and combustion rate in HCCI engine. The engine could be operated in HCCI combustion mode in a range of load from 1 to 5 bar IMEP and operated in SI combustion mode up to load of 8 bar IMEP. The HCCI combustion characteristics were investigated under different A/F ratios, engine speeds, starts of injection, as well as spark ignition enabled or not. The test results reveal the HCCI combustion features as a high-pressure gradient after ignition and has advantages in high thermal efficiency and low NOx emissions over SI combustion. At the part load of 1400rpm and IMEP of 3.5bar, ISFC in HCCI mode is 25% lower and NOx emissions is 95% lower than that in SI mode.

In order to meet increasingly stringent fuel consumption and emission regulations, more attentions are paid to improve engine efficiency. A large amount of energy-saving technologies have been applied in automotive field especially in gasoline engines. It is well known that lean burn and ultra-high compression ratio technologies are two basic and important methods to increase efficiency. In this paper, a rapid compression machine was employed to study combustion process of lean iso-octane mixture at ultra-high compression ratios (16 to 19:1). Regardless of flammability of the mixture, spark was triggered at the timing right after the end of compression, then, the flame propagation and/or auto-ignition can be recorded using high-speed photography simultaneously. The effects of equivalence ratio (φ), compression ratio (ε), dilution ratio, and effective temperature (Teff) on the combustion process was investigated.

Polyoxymethylene dimethyl ethers (PODEn) have high cetane number, high oxygen content and high volatility, therefore can be added to gasoline to optimize the performance and soot emission of Gasoline Compression Ignition (GCI) combustion. High speed imaging was used to investigate the spray and combustion process of gasoline/PODEn blends (PODEn volume fraction 0%-30%) under various ambient conditions and injection strategies in a constant volume vessel. Results showed that with an increase of PODEn proportion from 10% to 30%, liquid-phase penetration of the spray increased slightly, ignition delay decreased from 3.8 ms to 2.0 ms and flame lift off length decreased 29.4%, causing a significant increase of the flame luminance. For blends with 20% PODEn, when ambient temperature decreased from 893 K to 823 K, the ignition delay increased 1.3 ms and the flame luminance got lower.

The ignition of lubricating oil droplet has been proved to be the main factor for pre-ignition and the following super-knock in turbocharged gasoline direct injection engine. In this paper, the ignition process of lubricating oil droplet in combustible ambient gaseous mixture was investigated in a rapid compression machine (RCM). The pre-ignition induction by oil droplet of the ambient gaseous mixture was analyzed under different initial droplet volume and effective temperature conditions. The oil droplet was suspended on a tungsten fiber in the combustion chamber and the ignition process was recorded by a high-speed camera through the quartz window mounted at the end of the combustion chamber. The pressure traces were also obtained by a sensor in order to get the ignition delay and analyze the combustion process in detail.

A 1-Dimensional (1-D) model of fluid dynamic and chemistry kinetics following hot spot auto-ignition has been developed to simulate the process from auto-ignition to pressure wave propagation. The role of wall effect on the physical-chemical interaction process is numerically studied. A pressure wave is generated after hot spot auto-ignition and gradually damped as it propagates. The reflection of the wall forms a reflected pressure wave with twice the amplitude of the incident wave near the wall. The superposition of the reflected and forward pressure waves reinforces the intensity of the initial pressure wave. Wall effect is determined by the distance between the hot spot center and the cylinder wall. Hot spot auto-ignition near the wall easily initiates detonation under high-temperature and high-pressure conditions because pressure wave reflection couples with chemical reactions and propagates in the mixture with high reactivity.

A study of Multiple Premixed Compression Ignition (MPCI) with heavy naphtha is performed on a light-duty single cylinder diesel engine. The engine is operated at a speed of 1600rpm with the net indicated mean effective pressure (IMEP) from 0.5MPa to 0.9MPa. Commercial diesel is also tested with the single injection for reference. The combustion and emissions characteristics of the heavy naphtha are investigated by sweeping the first (−200 ∼ −20 deg ATDC) and the second injection timing (−5 ∼ 15 deg ATDC) with an injection split ratio of 50/50. The results show that compared with diesel combustion, the naphtha MPCI can reduce NOx, soot emissions and particle number simultaneously while maintaining or achieving even higher indicated thermal efficiency. A low pressure rise rate can be achieved due to the two-stage combustion character of the MPCI mode but with the penalty of high HC and CO emissions, especially at 0.5MPa IMEP.

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.

Stoichiometric dual-fuel compression ignition (SDCI) combustion has superior potential in both emission control and thermal efficiency. Split injection of diesel reportedly shows superiority in optimizing combustion phase control and increasing flexibility in fuel selection. This study focuses on split injection strategies in SDCI mode. The effects of main injection timing and pilot-to-total ratio are examined. Combustion phasing is found to be retarded in split injection when overmixing occurs as a result of early main injection timing. Furthermore, an optimised split injection timing can avoid extremely high pressure rise rate without great loss in indicated thermal efficiency while maintaining soot emission at an acceptable level. A higher pilot-to-total ratio always results in lower soot emission, higher combustion efficiency, and relatively superior ITE, but improvements are not significant with increased pilot-to-total ratio up to approximately 0.65.

A study of Multiple Premixed Compression Ignition (MPCI) with mixtures of gasoline and diesel is performed on a light-duty single cylinder diesel engine. The engine is operated at a speed of 1600rpm with the same fuel mass per cycle. By keeping the same intake pressure and EGR ratio, the influence of different blending ratios in gasoline and diesel mixtures (90vol%, 80vol% and 70vol% gasoline) is investigated. Combustion and emission characteristics are compared by sweeping the first (−95 ∼ −35deg ATDC) and the second injection timing (−1 ∼ 9deg ATDC) with an injection split ratio of 80/20 and an injection pressure of 80MPa. The results show that compared with diesel combustion, the gasoline and diesel mixtures can reduce NOx and soot emissions simultaneously while maintaining or achieving even higher indicated thermal efficiency, but the HC and CO emissions are high for the mixtures.

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.

Super knock which occurs in highly boosted spark ignition engines in low speed pre-ignition regime can lead to severe engine damage. However, super knock occurs occasionally, it is difficult to clearly identify the causes. The widely accepted assumption for the cause of this phenomenon is oil intrusion. Most of oils have been proved to have higher cetane number than n-heptane dose, indicating that the intruded oil is very liable to auto-ignition in a boosted engine. Although there have been reported the type of base oil and additive has significant effect on pre-ignition frequency, the oil induced super knock is still so far not supported by any direct evidence. This paper presents the effect of direct oil intrusion into cylinder on super knock. The experiment was carried out in a single cylinder engine. The diluted oil by gasoline with different ratio was directly injected into cylinder using a modified single-hole injector with 4MPa injection pressure.