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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.

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.

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.

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.

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.

The dual-fuel Reactivity Controlled Compression Ignition (RCCI) combustion could achieve high efficiency and low emissions over a wide range of operating conditions. However, further high load extension is limited by the excessive pressure rise rate and soot emission. Polyoxymethylene dimethyl ethers (PODE), a novel diesel alternative fuel, has the capability to achieve stoichiometric smoke-free RCCI combustion due to its high oxygen content and unique molecule structure. In this study, experimental investigations on high load extension of gasoline/PODE RCCI operation were conducted using late intake valve closing (LIVC) strategy and intake boosting in a single-cylinder, heavy-duty diesel engine. The experimental results show that the upper load can be effectively extended through boosting and LIVC with gasoline/PODE stoichiometric operation.

Homogeneous charge compression ignition (HCCI) is considered as a high efficient and clean combustion technology for I.C. engines. Methanol is a potential fuel for HCCI combustion. In this research, a single cylinder diesel engine was applied to HCCI operation. Methanol and dimethyl ether (DME) were fueled to the engine by fuel injection system with an electric controlled port in dual fuel mode. The results show that the stable HCCI operation of DME/methanol can be obtained over a quite broad speed and load region. And compared with higher speeds, the load region is even wider at low engine speed. E.g., at the engine speed of 1000 r/min, the maximum indicated mean effective pressure(IMEP) can reach 0.77 MPa, while at 2000r/min it is 0.53 MPa. Both DME and methanol influence HCCI combustion strongly, and by regulating DME/methanol proportions the HCCI combustion process could be controlled effectively.

Liquefied natural gas (LNG) engine could provide both reduced operating cost and reduction of greenhouse gas (GHG) emissions. Stoichiometric operation with EGR and the three-way catalyst has become a potential approach for commercial LNG engines to meet the Euro VI emissions legislation. In the current study, numerical investigations on the knocking tendency of several combustion chambers with different geometries and corresponding performances were conducted using CONVERGE CFD code with G-equation flame propagation model coupled with a reduced natural gas chemical kinetic mechanism. The results showed that the CFD modeling approach could predict the knock phenomenon in LNG engines reasonably well under different thermodynamic and flow field conditions.

In order to achieve high-efficiency and clean combustion in HCCI engines, combustion must be controlled reasonably. A great variety of species with various reactivities can be produced through low temperature oxidation of fuels, which offers possible solutions to the problem of controlling in-cylinder mixture reactivity to accommodate changes in the operating conditions. In this work, in-cylinder combustion characteristics with low temperature reforming (LTR) were investigated in an optical engine fueled with low octane number fuel. LTR was achieved through low temperature oxidation of fuels in a reformer (flow reactor), and then LTR products (oxidation products) were fed into the engine to alter the charge reactivity. Primary Reference Fuels (blended fuel of n-heptane and iso-octane, PRFs) are often used to investigate the effects of octane number on combustion characteristics in engines.

To investigate the effects of fuel volatility on combustion and emissions in a diesel engine, a high-volatility fuel of n-heptane was blended into diesel fuel with different volumetric fractions (0%, 40%, 70%, 100%). A wide range of EGR rates from 0% to 65% were investigated, which covered both the conventional diesel combustion and low temperature combustion. Experiments under two engine load conditions, ∼5.2 bar and ∼10.5 bar gross IMEP were performed at 1500 rpm. The injection timing was fixed at 8°CA BTDC for all test cases. Results show that even if the ignition delay and combustion duration are nearly the same for all tested fuels, the premixed combustion fractions are increased for higher volatility fuels due to the improvement on mixing process during the ignition delay period. The indicated specific fuel consumption is decreased as using high-volatility fuels. The effect of fuel volatility on soot emissions depends on engine loads.

Effects of fuel physical and chemical properties on combustion and emissions were investigated on both metal and optical diesel engines. The new generation oxygenated biofuels, n-butanol and DMF (2,5-dimethylfuran) were blended into diesel fuel with 20% volume fraction and termed as Butanol20 and DMF20 respectively. The exhaust gas recirculation (EGR) rates were varied from zero to ∼60% covering both conventional and low temperature combustion. Meanwhile, the reference fuels such as n-heptane, cetane, and iso-cetane were also used to isolate the effects of different fuel properties on combustion and emissions. In addition, to clarify the effects of oxygenated structures on combustion and emissions, a fundamental partially premixed burner was also used. Results based on metal and optical diesel engines show that fuel cetane number is the dominated factor to affect the auto-ignition timing and subsequent combustion process.

In this work, both the ‘SCR-only’ and ‘EGR+SCR’ technical routes are compared and evaluated after the optimizations of both injection strategy and turbocharging system over the World Harmonized Stationary Cycle (WHSC) in a heavy duty diesel engine. The exhaust emissions and fuel economy performance of different turbocharging systems, including wastegate turbocharger (WGT), variable geometry turbocharger (VGT), two-stage fixed geometry turbocharger (WGT+FGT) and two-stage variable geometry turbocharger (VGT+FGT), are investigated over a wide EGR range. The NOx reduction methods and EGR introduction strategies for different turbocharger systems are proposed to improve the fuel economy. The requirement on turbocharging system and their potential to meet future stringent NOx and soot emission regulations are also discussed in this paper.

The effects of cooled EGR on combustion and emission characteristics in HCCI operation region was investigated on a single-cylinder diesel engine, which is fitted with port injection of DME and methanol. The results indicate that EGR rate can enlarge controlled HCCI operating region, but it has little effect on the maximum load of HCCI engine fuelled with DME/methanol dual-fuels. With the increase of EGR rate, the main combustion ignition timing (MCIT) delays, the main combustion duration (MCD) prolongs, and the peak cylinder pressure and the peak rate of heat release decreases. Compared with EGR, DME percentage has an opposite effect on HCCI combustion characteristics. The increase of indicated thermal efficiency is a combined effect of EGR rate and DME percentage. Both HC and CO emissions ascend with EGR rate increasing, and decrease with DME percentage increasing. In normal combustion, NOX emissions are near zero.