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A yc6112ZLQ turbocharged 6 cylinder engine with intercooler was converted to operate in dual fuel mode with compressed natural gas (CNG) and pilot diesel. The influence of the CNG ratio, pilot diesel injection advance (ADC) and intake temperature after intercooler on the combustion process, emissions and engine performance was investigated. The results show that the combustion process of dual-fuel engines is faster than diesel engine. Both the ignition timing of the pilot fuel and the excess air ratio of total fuel λ dominate the combustion characteristics of duel-fuel engines. With the increase of CNG ratio, the pressure and temperature in cylinder decrease at rated mode, but increase at torque and low speed modes. With advanced the pilot injection timing or increased the intake temperature, the cylinder pressure and temperature increase.

Hybrid powertrain has been proven to be an effective fuel-saving technology in commercial vehicles, but many hybrid commercial vehicles still use conventional diesel engines, resulting in limited fuel savings. The main purpose of this study is to enhance the thermal efficiency of a dedicated hybrid diesel engine focusing on the characteristic operating conditions. Via fundamental thermodynamics process analysis of internal combustion engine, steel piston with high compression ratio, air system involving two-stage turbocharger(2TC) with an intercooler, and late intake valve closing(IVC) timing are proposed to improve the thermal efficiency of the engine. Experimental results show that high compression ratio and lower thermal conductivity of the combustion chamber surface lead to lower heat release rates, requiring optimization of piston profile to accelerate the mixing rate. Besides, high compression ratio also leads to higher mechanical losses.

The influence of boost pressure (Pin) and fuel chemistry on combustion characteristics and performance of homogeneous charge compression ignition (HCCI) engine was experimentally investigated. The tests were carried out in a modified four-cylinder direct injection diesel engine. Four fuels were used during the experiments: 90-octane, 93-octane and 97-octane primary reference fuel (PRF) blend and a commercial gasoline. The boost pressure conditions were set to give 0.1, 0.15 and 0.2MPa of absolute pressure. The results indicate that, with the increase of boost pressure, the start of combustion (SOC) advances, and the cylinder pressure increases. The effects of PRF octane number on SOC are weakened as the boost pressure increased. But the difference of SOC between gasoline and PRF is enlarged with the increase of boost pressure. The successful HCCI operating range is extended to the upper and lower load as the boost pressure increased.

By mixing iso-octane with octane number 100 and normal heptane with octane number 0, it was possible to obtain a PRF fuel with octane rating between 0 and 100. The influence of PRF fuel’s octane number on the combustion characteristics, performance and emissions character of homogeneous charge compression ignition (HCCI) engine was investigated. The experiments were carried out in a single cylinder direct injection diesel engine. The test results show that, with the increase of the octane number, the ignition timing delayed, the combustion rate decreased, and the cylinder pressure decreased. The HCCI combustion can be controlled and then extending the HCCI operating range by burning different octane number fuel at different engine mode, which engine burns low octane number fuel at low load mode and large octane number fuel at large load mode. There exists an optimum octane number that achieves the highest indicated thermal efficiency at different engine load.

In order to achieve high efficiency and clean combustion indiesel engines, many advanced combustion concepts have been developed to simultaneously reduce NOx and soot emissions with high efficiency. However, the benefits of these combustion modes are limited to low loads because the energy release ratesaretoo fast at high loads. Recently, Dual-fuel highly premixed charge combustion (HPCC) strategies with the port injection of gasoline and direct injection of diesel have demonstrated advantages in terms of extending the operating range by the flexible control of fuel chemical reactivity and charge stratification. However, the extension to high-load in a turbocharged multi-cylinder diesel engine with the HPCC is a critical challenge due to excessive pressure rise rates. Mean while it suffers from the excessive of CO/HC emissions at low loads.

Gasoline partially premixed combustion (PPC) is a potential combustion concept to achieve high engine efficiency as well as low NOx and soot emissions. But the in-cylinder process of PPC is not well understood. In the present study, the double injection strategy of PPC was investigated on a light-duty optical engine. The fuel/air mixing and combustion process of PPC was evaluated by fuel-tracer planar laser-induced fluorescence (PLIF) and high-speed natural luminosity imaging technique, respectively. Combustion emission spectra of typical double injection case were analyzed. The primary reference fuel, PRF70 (70% iso-octane and 30% n-heptane by volume) was chosen as the lower reactivity fuel like gasoline. Double injection strategies of different first fuel injection timing and mass ratio of the two fuel injections were comparatively studied.

Biodiesel is a widely used biofuel in diesel engines, which is of particular interest as a renewable fuel because it possesses the similar properties as the diesel fuel. The pure soybean biodiesel was tested in an optical constant volume combustion chamber using natural flame luminosity and forward illumination light extinction (FILE) methods to explore the combustion process and soot distribution at various ambient temperatures (800 K and 1000 K) and oxygen concentrations (21%, 16%, 10.5%). Results indicated that, with a lower ambient temperature, the autoignition delay became longer for all three oxygen concentrations and more ambient air was entrained by spray jet and more fuel was burnt by premixed combustion. With less ambient oxygen concentration, the heat release rate showed not only a longer ignition delay but also longer combustion duration.

A very competitive alcohol for use in diesel engines is butanol. Butanol is of particular interest as a renewable bio-fuel, as it is less hydrophilic and it possesses higher heating value, higher cetane number, lower vapor pressure, and higher miscibility than ethanol or methanol. These properties make butanol preferable to ethanol or methanol for blending with conventional diesel or gasoline fuel. In this paper, the spray and combustion characteristics of pure n-butanol fuel was experimentally investigated in a constant volume combustion chamber. The ambient temperatures were set to 1000 K, and three different oxygen concentrations were set to 21%, 16%, and 10.5%. The results indicate that the penetration length reduces with the increase of ambient oxygen concentration. The combustion pressure and heat release rate demonstrate the auto-ignition delay becomes longer with decreasing of oxygen concentrations.

Reactivity controlled compression ignition (RCCI) is a potential combustion strategy to achieve high engine efficiency with ultra-low NOx and soot emissions. Fuel stratification can be used to control the heat release rate of RCCI combustion. But the in-cylinder combustion process of the RCCI under different fuel stratification degrees has not been well understood, especially at a higher engine load. In this paper, simultaneous measurement of natural flame luminosity and emission spectra was carried out on a light-duty optical RCCI engine under different fuel stratification degrees. The engine was run at 1200 revolutions per minute under a load about 7 bar indicated mean effective pressure (IMEP). In order to form fuel stratification degrees from low to high, the common-rail injection timing of n-heptane was changed from -180° CA after top dead center (ATDC) to -10° CA ATDC, while the iso-octane delivered in the intake stroke was fixed.

With a zero-dimensional detailed chemical kinetic model, a numerical study was carried out to investigate the chemical reaction phenomena encountered in the homogenous charge compression ignition process of dimethyl ether (DME) and methane dual fuel. The results show that the DME/methane dual fuel elementary reactions affect each other. The low temperature reaction (LTR) of DME is inhibited, the second molecular oxygen addition of DME is restrained, and β -scission plays a dominant role in DME oxidation. Hydrogen peroxide (H2O2) is controlled by DME oxidation and almost has no correlation with methane oxidation. The rich H2O2 concentration makes methane oxidation occurs at low initial temperature. Most of the formaldehyde (CH2O) is produced from H-abstraction of methoxy (CH3O) rather than from LTR of the DME. However, the heat release of methane oxidation promotes the hot flame reactions of DME which make the reactions with high activation energy occur.

OH, soot and temperature distributions of wall-impinging diesel fuel spray were investigated in a high-temperature high-pressure constant volume combustion vessel. The ambient temperature (Ta) was set as 773 K, and the wall temperature (Tw) was set as 523 K, 673 K, 773 K, respectively. Three different injection pressures (Pi) of 60 MPa, 100 MPa, 160 MPa, and the ambient pressures (Pa) of 4 MPa were applied. The OH spatial distributions of wall-impinging spray were measured by the method of OH chemiluminescence imaging. Two-color pyrometry was applied to evaluate the spatial distributions of KL factor and flame temperature of wall-impinging spray. The results reveal that, OH chemiluminescence is observed in the region near the impingement point firstly. The regions of high OH chemiluminescence intensity and high KL factor appear in the location near the wall surface along the whole combustion process.

In the current, numerical study RCCI combustion and emission characteristics using various fuel strategies are investigated, including methanol, ethanol, n-butanol and gasoline as the low reactivity fuel, and diesel fuel as the high reactivity fuel. A reduced Primary Reference Fuel (PRF)-alcohol chemical kinetic mechanism was coupled with a computational fluid dynamic (CFD) code to predict RCCI combustion under various operating conditions. The results show that a higher quantity of diesel was required to maintain the same combustion phasing with alcohol-diesel fuel blends, and the combustion durations and pressure rise rates of methanol-diesel (MD) and ethanol-diesel (ED) cases were much shorter and higher than those of gasoline-diesel (GD) and n-butanol-diesel (nBD) cases. The simulations also investigated the sensitivities of the direct injection strategies, intake temperature and premixed fuel ratio on RCCI combustion phasing control.

Reactivity Controlled Compression Ignition (RCCI) has been shown to be an attractive concept to achieve clean and high efficiency combustion. RCCI can be realized by applying two fuels with different reactivities, e.g., diesel and gasoline. This motivates the idea of using a single low reactivity fuel and direct injection (DI) of the same fuel blended with a small amount of cetane improver to achieve RCCI combustion. In the current study, numerical investigation was conducted to simulate RCCI and HCCI combustion and emissions with various fuels, including gasoline/diesel, iso-butanol/diesel and iso-butanol/iso-butanol+di-tert-butyl peroxide (DTBP) cetane improver. A reduced Primary Reference Fuel (PRF)-iso-butanol-DTBP mechanism was formulated and coupled with the KIVA computational fluid dynamic (CFD) code to predict the combustion and emissions of these fuels under different operating conditions in a heavy duty diesel engine.

This work numerically investigates the detailed combustion kinetics of partially premixed combustion (PPC) in a diesel engine under three different premixed ratio fuel conditions. A reduced Primary Reference Fuel (PRF) chemical kinetics mechanism was coupled with CONVERGE-SAGE CFD model to predict PPC combustion under various operating conditions. The experimental results showed that the increase of premixed ratio (PR) fuel resulted in advanced combustion phasing. To provide insight into the effects of PR on ignition delay time and key reaction pathways, a post-process tool was used. The ignition delay time is related to the formation of hydroxyl (OH). Thus, the validated Converge CFD code with the PRF chemistry and the post-process tool was applied to investigate how PR change the formation of OH during the low-to high-temperature reaction transition. The reaction pathway analyses of the formations of OH before ignition time were investigated.

The application of oxygen-enriched or oxy-fuel combustion coupled with carbon capture and storage technology has zero carbon dioxide emission potential in the boiler and gas turbine of the power plant. However, the oxygen-enriched combustion with high oxygen level has few studies in internal combustion engines. The fundamental issues and challenges of high oxygen level are the great differences in the physical properties and chemical effects compared with the combustion in air condition. As a consequence, the diesel spray combustion characteristics at high oxygen level were investigated in an optical constant volume vessel. The oxygen volume fraction of tested gas was from 21% to 70%, buffered with argon. The high-speed color camera was used to record the natural flame luminosity.

The effects of various injection timing of methanol on thermo-atmosphere combustion of methanol by port injection of dimethyl ether (DME) and direct injection of methanol were experimentally investigated. The experiment results show that, as injection timing is at 6 degree before TDC, the combustion process comprises three stages: low temperature heat release of DME, high temperature heat release of DME and diffusion combustion of methanol. As injection timing increases, premixed combustion proportion of methanol is increased and diffusion combustion proportion is decreased. As injection timing increases to 126 degree before TDC, diffusion combustion of methanol disappears. At this time, the combustion process shows typical two stages heat release of HCCI combustion. As injection timing increases, required DME rate is increased, combustion efficiency and indicated thermal efficiency all first increase and then decrease.

In this work the gasoline compression ignition (GCI) combustion characterized by both premixed gasoline port injection and gasoline direct injection in a single-cylinder diesel engine was investigated experimentally and computationally. In the experiment, the premixed ratio (PR), injection timing and exhaust gas recirculation (EGR) rate were varied with the pressure rise rate below 10 bar/crank angle. The experimental results showed that higher PR and earlier injection timing resulted in advanced combustion phasing and improved thermal efficiency, while the pressure rise rates and NOx emissions increased. Besides, a lowest ISFC of 176 g/kWh (corresponding to IMEP =7.24 bar) was obtained, and the soot emissions could be controlled below 0.6 FSN. Despite that NOx emission was effectively reduced with the increase of EGR, HC and CO emissions were high. However, it showed that GCI combustion of this work was sensitive to EGR, which may restrict its future practical application.

This work concerns the oxidation of biodiesel surrogates in a CI engine. An experimental study has been carried out in a single-cylinder common-rail CI engine with soybean biodiesel and two biodiesel surrogates containing neat methyl decanoate and methyl decanoate/n-heptane blends. Tests have been conducted with various intake oxygen concentrations ranging from 21% to approximately 9% at intake temperatures of 25°C and 50°C. The results showed that the ignition delay and smoke emissions of neat methyl decanoate were closer to that of soybean biodiesel as compared with methyl decanoate/n-heptane blends. A reduced chemical kinetic mechanism for the oxidation of methyl decanoate has been developed and applied to model internal combustion engines. A KIVA code, coupled with the Chemkin chemistry solver, was used as the computational platforms. The effects of various intake oxygen concentrations on the in-cylinder emissions of OH and soot were discussed.

The effects of Exhaust Gas Recirculation (EGR) and octane number of PRF fuel on combustion and emission characteristics in HCCI operation were investigated. The results show that EGR could delay the ignition timing, slow down the combustion reaction rate, reduce the pressure and average temperature in cylinder and extend the operation region into large load mode. With the increase of the fuel/air equivalence ratio or the fuel octane number (ON), the effect of EGR on combustion efficiency improves. With the increase of EGR rate, the combustion efficiency decreases. The optimum indicated thermal efficiency of different octane number fuels appears in the region of high EGR rate and large fuel/air equivalence ratio, which is next to the boundary of knocking. In the region of high EGR rate, HC emissions rise up sharply as the EGR rate increases. With the increase of octane number, this tendency becomes more obvious.

Studies on combustion process of Dimethyl Ether (DME) were carried out on a constant volume combustion bomb (CVCB) and a visualization engine, and the photograph of combustion of DME was taken by high speed digital CCD. The results show that the ignition delay of DME is shorter than that of diesel fuel. When the fuel delivery amounts of DME and diesel in volume are the same, the combustion duration of DME is shorter than that of diesel fuel, and the flame temperature of DME is lower than that of diesel. At the end of combustion, the second injection occurred. The results of high-speed photograph in visualization engine show that, as soon as DME leaves the nozzle, it evaporates rapidly, and under the effect of air swirl, the spray“core” is blown off. Compared to diesel, the penetration of DME is shorter, and the wall combustion of DME is apparently smaller.