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A new approach of NOx reduction in the compression-ignition engine is introduced in this work. The previous research has shown that during the combustion stage, the high temperature ignition tends to occur early at the near-stoichiometric region where the combustion temperature is high and majority of NOx is formed; Therefore, it is desirable to burn the leaner region first and then the near-stoichiometric region, which inhibits the temperature rise of the near-stoichiometric region and consequently suppresses the formation of NOx. Such inverted ignition sequence requires mixture with inverted phi-sensitivity. Fuel selection is performed based on the criteria of strong ignition T-sensitivity, negligible negative temperature coefficient (NTC) behavior, and large heat of vaporization (HoV).

Recently, with the increasing interest on some potential alternative substitutes of petroleum fuels such as biodiesel and butanol, more and more researches are focused on the field of bio-fuels because they are renewable and friendly to the environment and can possibly reduce domestic demand on foreign petroleum. Bio-fuels are generally used in the commercial market by mixing with petroleum-based diesel or gasoline. Since the volatilities and boiling points of ethanol/butanol and diesel/biodiesel fuels are significantly different, micro-explosion can be expected in the blend mixture. In this study, a numerical model of micro-explosion including bubble generation, bubble expansion, and final breakup for multi-component bio-fuel droplets is proposed. From the simulated results of droplet characteristics at the onset of micro-explosion, it is concluded that micro-explosion is possible under engine operation condition for ethanol/butanol-diesel/biodiesel fuel blends.

The formation of fuel film in the combustion cylinder affects the mixing process of the air and the fuel, and the process of the combustion propagation in engines. Some models of film evaporation have been developed to predict the evaporation behavior of the film, but rarely experimental results have been produced, especially when the temperature is high. In this study, the evaporation behavior of the film of different species of oil and their blends at different temperature are observed. The 45 μL films of isooctane, 1-propanol, 1-butanol, 1-pentanol, and their blends were placed on a quartz glass substrate in the closed temperature-controlled chamber. The shape change of the film during evaporation was monitored by a high-speed camera through the window of the chamber. First, the binary blends film of isooctane and one of the other three oils were evaporated at 30 °C, 50 °C, 70 °C and 90 °C.

Flash boiling has drawn much attention recently for its ability to enhance spray atomization and vaporization, while providing better fuel/air mixing for gasoline direct injection engines. However, the behaviors of flash boiling spray with multi-component fuels have not been fully discovered. In this study, isooctane, ethanol and the mixtures of the two with three blend ratios were chosen as the fuels. Measurements were performed with constant fuel temperature while ambient pressures were varied to adjust the superheated degree. Macroscopic and microscopic characteristics of flash boiling spray were investigated using Diffused Back-Illumination (DBI) imaging and Phase Doppler Anemometry (PDA). Comparisons between flash boiling sprays with single component and binary fuel mixtures were performed to study the effect of fuel properties on spray structure as well as atomization and vaporization processes.

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.

Little research has been done on spray characteristics of 2,5-dimethylfuran (DMF), since the breakthrough in its production method as an alternative fuel candidate. In this paper, the spray characteristics of pure fuels (DMF, Isooctane) and DMF-Isooctane blends under different ambient pressures (1 bar, 3 bar and 7 bar) and injection pressures (50 bar, 100 bar and 150 bar) were studied using Phase Doppler Particle Analyzer (PDPA) and high speed imaging. Droplet velocity, size distribution, spray angle and penetration of sprays were examined. Based on the results, DMF had larger SMD and penetration length than isooctane. The surface tension of fuel strongly influenced spray characteristics. Increasing the surface tension by 26 % resulted in 12 % increase in SMD. Higher ambient pressure increased the drag force, but SMD was not influenced by the increased drag force. However, the increased ambient pressure reduced the injection velocity and We number resulting in higher SMD.

Transient emissions of a turbocharged three-litre V6 diesel engine fuelled by hydrogenated vegetable oil (HVO) blends were experimentally investigated and compared with transient emissions of diesel as reference. The transient emissions measurements were made by highly-dynamic emissions instrumentations including Cambustion HFR500, CLD500 and DMS500 particulate analyzer. The HVO blends used in this study were 30% and 60% of HVO in diesel by volume. The transient conditions were simulated by load increases over 5 s, 10 s and 20 s durations at a constant engine speed. The particulate, NO, HC concentrations were measured to investigate the mechanism of emission formation under such transient schedules. The results showed that as the load increased, NO concentrations initially had a small drop before dramatically increasing for all the fuels investigated which can be associated with the turbocharger lag during the load transient.

An experimental study of particulate matter (PM) emission was conducted on four cars from Chinese market. Three cars were powered by gasoline direct injection (GDI) engines and one car was powered by a port fuel injection (PFI) engine. Particulate mass, number and size distribution were measured based on a chassis dynamometer over new European driving cycle (NEDC). The particulate emission behaviors during cold start and hot start NEDCs were compared to understand how the running conditions influence particulate emission. Three kinds of gasoline with RON 91.9, 94.0 and 97.4 were tested to find the impact of RON on particulate emission. Because of time and facilities constraints, only one cold/hot start NEDC was conducted for every vehicle fueled with every fuel. The test results showed that more particles were emitted during cold start condition (first 200s in NEDC). Compared with cold start NEDC, the particulate mass and number of hot start NEDC decreased by a wide margin.

Homogeneous charge combustion and emissions of ethanol ignited by pilot diesel fuel were investigated on a two-cylinder diesel engine. The results show that emissions depend on loads and ethanol volume fraction. At low loads, ethanol has little effects on smoke. With the increase of ethanol, NOx decreases, but CO emissions increase. At high loads, smoke emissions reduce greatly with increasing ethanol, but NOx and total hydrocarbon (THC) emissions increase. With the increase of ethanol, ignition delays, combustion duration shortens. The maximum rates of heat release for the fuel containing 10 vol% ethanol (E10) and 30 vol% ethanol (E30) increase. Brake specific energy consumption (BSEC) of E10 and E30 is improved slightly only at full loads. Compared to smoke emissions obtained on the same engine using ethanol blended diesel fuels, the tendency of smoke reduction is similar to that of homogeneous charge combustion of ethanol at the same operating conditions.

Inverted phi (ϕ)-sensitivity is a new approach of NOx reduction in compression-ignition (C.I.) engines. Previously, pure ethanol (E100) was selected as the preliminary test fuel in a single injection compression-ignition engine, and was shown to have good potential for low engine-out NOx emissions under low and medium load conditions due to its inverted ignition sequence. Under high load, however, the near-stoichiometric and non-homogeneous fuel/air distribution removes the effectiveness of the inverted ϕ-sensitivity. Therefore, it is desirable to recover the combustion sequence in the chamber such that the leaner region is burned before the near-stoichiometric region. When the combustion in near-stoichiometric region is inhibited, the temperature rise of that region is hindered and the formation of NOx is suppressed.

A multi-step acetone-butanol-ethanol (ABE) phenomenological soot model was proposed and implemented into KIVA-3V Release 2 code. Experiments were conducted in an optical constant volume combustion chamber to investigate the combustion and soot emission characteristics under the conditions of 1000 K initial temperature with various oxygen concentrations (21%, 16%, 11%). Multi-dimensional computational fluid dynamics (CFD) simulations were conducted in conjunction under the same operation conditions. The predicted soot mass traces showed good agreement with experimental data. As ambient oxygen decreased from 21% to 11%, ignition delay retarded and the distribution of temperature became more homogenous. Compared to 21% ambient oxygen, the peak value of total soot mass at 16% oxygen concentration was higher due to the suppressed soot oxidation mechanism.

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.

The diesel particulate filter (DPF) is an effective technology for particulate matter (PM) and particle number (PN) reduction. On heavy-duty diesel engines, the passive regeneration by Diesel Oxidation catalysts (DOC) and catalyzed DPFs (CDPF) is widely used for its simplicity and low cost, which is generally combined with the active regeneration of exhaust fuel injection. This study investigated a DOC-CDPF system with exhaust fuel injection upstream of the DOC. The system was integrated with a 7-liter diesel engine whose engine-out PM emission was below the Euro IV level and tested on an engine dynamometer. PM and PN concentrations were measured based on the Particle Measurement Programme (PMP), and the number/size spectrum for particles was obtained by a Differential Mobility Spectrometer (DMS). The filtration efficiency of DPF on PN was higher than 99% in ESC test, while the efficiency on PM was only 58%.

Diesel particulate filter (DPF) is indispensable for diesel engines to meet the increasingly stringent emission regulations. Both the peak temperature and the maximum temperature gradient of the DPF during active regeneration should be well controlled in order to enhance the reliability and durability of the filter. In this paper, the temperature field of the DPF during active regeneration with hydrocarbon (HC) injection was investigated with engine bench tests and numerical simulation. For the experimental study, 24 thermocouples were inserted into the DPF channels to measure the inner temperature of the filter to capture its temperature field, and the circumferential, axial and radial distribution of the filter temperature was analyzed to understand the DPF temperature field behavior during active regeneration.

Combustion behaviour and emissions characteristics of different blending ratios of diesel and gasoline fuels (Dieseline) were investigated in a light-duty 4-cylinder compression-ignition (CI) engine operating on partially premixed compression ignition (PPCI) mode. Experiments show that increasing volatility and reducing cetane number of fuels can help promote PPCI and consequently reduce particulate matter (PM) emissions while oxides of nitrogen (NOx) emissions reduction depends on the engine load. Three different blends, 0% (G0), 20% (G20) and 50% (G50) of gasoline mixed with diesel by volume, were studied and results were compared to the diesel-baseline with the same combustion phasing for all experiments. Engine speed was fixed at 1800rpm, while the engine load was varied from 1.38 to 7.85 bar BMEP with the exhaust gas recirculation (EGR) application.

An experimental investigation was conducted using a Ford single-cylinder spark-ignition research engine to compare the performance and emissions of neat n-butanol fuel to that of gasoline and ethanol. Measurements of brake torque and exhaust gas temperature along with in-cylinder pressure traces were used to study the performance of the engine and measurements of emissions of unburned hydrocarbons, carbon monoxide, and nitrogen oxide ere used to compare the three fuels in terms of combustion byproducts. It was found that gasoline and butanol are closest in engine performance with butanol producing slightly less brake torque. Exhaust gas temperature and nitrogen oxide measurements show that butanol combusts at a lower peak temperature. Of particular interest were the emissions of unburned hydrocarbons which were between two and three times those of gasoline suggesting that butanol is not atomizing as effectively as gasoline and ethanol.

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.

An optically accessible single-cylinder high-speed direct-injection (HSDI) diesel engine equipped with a Bosch common rail injection system was used to study effects of injection pressures on the in-cylinder spray and combustion processes. An injector with an injection angle of 70 degrees and European low sulfur diesel fuel (cetane number 54) were used in the work. The operating load was 2.0 bar IMEP with no EGR added in the intake. The in-cylinder pressure was measured and the heat release rate was calculated. High-speed Mie-scattering technique was employed to visualize the liquid distribution and evolution. High-speed combustion video was also captured for all the studied cases using the same frame rate. NOx emissions were measured in the exhaust pipe. The experimental results indicated that for all of the conditions the heat release rate was dominated by a premixed combustion pattern. Two-stage low temperature reaction was seen for early injection timings.

In this paper, the impacts of Aromatic and Olefin on the formation of poly-aromatic hydrocarbons (PAHs) in the gasoline direct injection (GDI) engine were experimentally and numerically investigated. The objective of this study is to describe the formation process of the soot precursors including one ring to four ring aromatics (A1-A4). In order to better understand the effects of the fuel properties on the formations of PAHs. Three types of fuels, namely base gasoline, gasoline with higher aromatics content, and gasoline with higher olefin content were experimentally studied. At the same time, these aspects were also numerically investigated in the CHEMKIN code by using premixed laminar flame model and surrogated fuels. The results show that higher aromatics content in gasoline will lead to much higher PAHs formation. Similar trend was also found in the gasoline with higher olefin content.

HTL is a kind of biodiesel converted from wet biowaste via hydrothermal liquefaction (HTL), which has drawn increasing attention in recent years due to its wide range of raw materials (algae, swine manure, and food processing waste). However, from the previous experiments done in a constant volume chamber, it was observed that the presence of 20% of HTL in the blend produced as much soot as pure diesel at in chamber environment oxygen ratio of 21%, and even more soot at low oxygen ratios. It was also observed that n-butanol addition could reduce the soot emission of diesel significantly under all tested conditions. In this work, the spray and combustion characteristics of HTL and diesel blends with n-butanol added were investigated in a constant volume chamber. The in-chamber temperature and oxygen ranged from 800 to 1200 K and 21% to 13%, respectively, covering both conventional and low-temperature combustion (LTC) regimes.