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Technical Paper

Study on the Laminar Characteristics of Ethanol, n-Butanol and n-Pentanol Flames

Due to serious energy crisis and pollution problem, interest in research of the alternative fuels is increasing over the world. Alcohol fuels are always considered to be promising alternative fuels. Lower alcohols owning high octane number is good octane enhancer for SI (Spark ignition) engine, however is difficult to be used in CI (Compression Ignition) engines. Higher alcohols like pentanol with higher energy content, poor water solubility and higher cetane number are good choice for the CI engines. In this study, laminar flame behaviors of ethanol-air, n-butanol-air and n-pentanol-air mixtures at 393 K and 0.1 MPa are compared and analyzed with the spherical propagating flames. Comparison of the laminar flame speeds measured in the previous studies (Li et al.) show that laminar flame speed of ethanol is the fastest with slower flame speed of n-butanol and n-pentanol at lean mixture. At rich mixture, three alcohols present very close values.
Technical Paper

Measurement on Turbulent Premixed Flame Structure of CH4/H2/Air Mixtures with CO2 Dilution

Measurement on turbulent premixed CH4/H2/air flames was studied experimentally. Hydrogen blending ratio is defined as the ratio of hydrogen to fuel, while CO2 dilution ratio is defined as the mole fraction of CO2 to those of mixture. Hydrogen blending ratios up to 0.2 and CO2 dilution ratios up to 0.1 were studied. OH profile of the instantaneous flame front was detected using the OH-PLIF visualizations on a turbulent Bunsen burner. 500 OH-PLIF images were used to obtain the turbulent burning velocity and calculate flame surface density, and 280 images was used to calculate the local curvature radius.
Technical Paper

Specific Heat Ratio of High Methane Fraction Natural Gas/Air in Confined Vessel

The specific heat ratio used in heat release calculation plays an important role and the mass fraction burned is also a crucial parameter in thermodynamics analysis for engine combustion. A research of high methane fraction natural gas was investigated in a constant volume combustion vessel at different initial conditions. Results show that with the increase of the initial pressure, the specific heat ratio is decreased, and the time of the mixture burned up is postponed, while the peak heat release ratio is increased. With the increase of the methane fraction, the parameters have the opposite behavior. With the increase of the initial temperature, the specific heat ratio is decreased, and the time when the mixture is burned up is accelerated, and the peak heat release ratio has no obviously difference. With the increase of the dilution ratio or the CO2/N2 ratio, the specific heat ratio is decreased, and the peak heat release heat ratio is decreased.
Technical Paper

Comparative Study of High-Alcohol-Content Gasoline Blends in an SI Engine

Ethanol is the most widely used renewable fuel in the world now. Compared to ethanol, butanol is another very promising renewable fuel for internal combustion engines. It is less corrosive, and has higher energy density, lower vapor pressure and lower solubility in water. However, the use of Acetone-Butanol-Ethanol (ABE), an intermediate product in ABE fermentation, presents a cost advantage over ethanol and butanol and has attracted much attention recently. In this study, three high-alcohol-content gasoline blends (85% vol. of ethanol, butanol and ABE, referred as E85, B85 and ABE85, respectively) were investigated in a port-injection spark-ignition engine. ABE has a component ratio of 3:6:1. In addition, pure gasoline was also tested as a baseline for comparison. All fuels were tested under the same conditions (1200 RPM, Φ = 0.83−1.25, BMEP = 3 bar).
Journal Article

Experimental and Kinetic Study on Ignition Delay Times of Diethyl Ether

Ignition delay times of Diethyl Ether (DEE) were measured behind reflected shock waves for the temperatures from 1050 to 1600 K, pressures of 1.2, 4 and 16 atm and equivalence ratios of 0.5 and 1.0. Result shows that the ignition delay times increase with the increase of the equivalence ratio and the decrease of the pressure. The only literature DEE mechanism (Yasunaga et al. model) was employed to simulate the experimental data and result shows that the model gives reasonable prediction on lean mixtures, while the prediction on stoichiometric mixtures is slightly higher. Sensitivity analysis was conducted to pick out the key reactions in the process of DEE ignition at high and low pressures, respectively. Reaction pathway analysis shows that the consumption of DEE is dominated by the H-abstraction reactions. Through linear analysis, a correlation for the DEE ignition data was obtained.
Technical Paper

Comparative Analysis on Performance and Particulate Emissions of a Turbocharged Common-Rail Engine Fueled with Diesel and Biodiesels

Performance and particulate emissions of a modern common-rail and turbocharged diesel engine fueled with diesel and biodiesel fuels were comparatively studied. An electrical low-pressure impactor (ELPI) was employed to measure particle size distribution and number concentration. Two biodiesel fuels, BDFs (biodiesel from soybean oil) and BDFc (biodiesel from used cooking oil), as well as ultra-low sulfur diesel were used. The study shows that biodiesels give higher thermal efficiency than diesel. Biodiesels give obviously lower exhaust gas temperature than diesel under high engine speed. The differences in fuel consumption, thermal efficiency and exhaust gas temperature between BDFs and BDFc are negligible. The first peaks of heat release rate for biodiesels are lower than that of diesel, while the second peaks are higher and advanced for biodiesels. BDFs show slightly slower heat release than BDFc during the first heat release stage at low engine speed.
Journal Article

Influence of Biodiesel/Diesel Blends on Particulate Emissions in a Turbocharged Common Rail Diesel Engine

Experiments were conducted in a turbocharged, high-pressure common rail diesel engine to investigate particulate emissions from the engine fueled with biodiesel and diesel blends. An electrical low-pressure impactor (ELPI) was employed to measure the particle size distribution and number concentration. Heated dilution was used to suppress nuclei mode particles and focus on accumulation mode particles. The experiment was carried out at five engine loads and two engine speeds. Biodiesel fractions of 10%, 20%, 40%, 60% and 80% in volume were tested. The study shows that most of the particles are distributed with their diameters between 0.02 and 0.2 μm, and the number concentration becomes quite small for the particles with the diameters larger than 0.2 μm. With the increase of biodiesel fraction, engine speed and/or engine load, particle number concentration decreases significantly, while the particle size distribution varies little.
Technical Paper

Experimental and Modeling Study on Auto-Ignition of DME/n-Butane Blends under Engine Relevant Pressure

In this study, the ignition delay times of DME/n-C4H10 fuel blends (neat DME, 50/50 and neat n-C4H10) diluted with argon were measured behind reflected shock waves. The experiments were performed in the temperature range of 1250 - 1600 K, at pressure of 2.0 MPa and equivalence ratios from 0.5 to 2.0. A latest kinetic mechanism NUIG Aramco Mech 1.3 was validated against the present ignition data and used to conducted chemical kinetic analysis. Different equivalence-ratio-dependent was exhibited at different temperature regimes for DME, n-C4H10, and their blend. Fuel flux analysis, sensitive analysis and mole fraction analysis were carried out for understanding the interaction between the ignition chemistries of DME and n-C4H10.
Technical Paper

Study on Ignition Delay Times of DME and n-Butane Blends

Ignition delay times of stoichiometric dimethyl ether (DME) and n-butane blends were measured in a shock tube at varied DME blending ratios, temperatures and pressures. Simulation work extended the pressure to 20 atm by using Chemkin and NUI C4_47 mechanism. The experimental ignition delay times of DME/n-butane were obtained at different DME blending ratios. Measured ignition delay times were compared to simulations based on NUI C4_47 mechanisms by Curran et al. The mechanism predicts the magnitude of ignition delay times well and a slightly higher activation energy. The ignition delay times increase linearly with the increase of 1000/T and the overall activation energy keeps almost the same value at the conditions in this study. Increasing pressure decreases exponentially the ignition delay time. Ignition delay time decreases linearly with the increase of DME blending ratio.
Journal Article

Effect of Hot Exhaust Gas Recirculation on the Combustion Characteristics and Particles Emissions of a Pilot-Ignited Natural Gas Engine

Natural gas has become an attractive alternative for diesel fuel due to its higher octane number, richer reserves and lower price. It has been utilized in compression ignition engines to obtain a higher thermal efficiency compared with spark ignition engines. However, its relatively higher auto-ignition temperature increases the difficulty of compression-ignition based on present hardware devices. One optimal ignition method is that a very small quantity of diesel fuel as the only ignition resource pilot-ignites the lean natural gas-air mixture. This micro diesel pilot-ignited natural gas premixed charge compression ignition (DPING-PCCI) combustion strategy is easy to implement without major hardware modifications, and can significantly reduce the NOx and particle mass emissions from diesel engines. Although the DPING-PCCI has so many advantages, it suffers from poor engine stability and high ultrafine particles emissions at part loads.
Journal Article

A Comparative Study of Two Kinds of Biodiesels and Biodiesel-DEE Blends in a Common Rail Diesel Engine

Ultrafine particles and NOx emissions of two kinds of biodiesels and their blends with diethyl ether (DEE) as an additive were compared under two engine speeds and three loads on a turbocharged, high-pressure, common rail diesel engine. A single spray injection and equivalence ratio distribution are used to explain the results. The study shows that biodiesel and biodiesel-DEE blend consume more fuels than diesel but slight variation in thermal efficiency. NOx emissions of waste cooking oil biodiesel are less than those of soybean biodiesel. At low and medium loads, DEE blending reduces the NOx emission. At all engine loads and speeds, the shape of ultrafine particle number distribution curve is unimodal, and fuel type slightly affects the shape of distribution curves. The number/mass distribution curves shift to fewer particles when operating on biodiesel and the curves further move to downward when DEE is added.
Journal Article

Effect of Injection Pressure on Ignition, Flame Development and Soot Formation Processes of Biodiesel Fuel Spray

The effect of injection pressure ranging from 100 to 300MPa on the ignition, flame development and soot formation characteristics of biodiesel fuel spray using a common rail injection system for direct injection (D.I.) diesel engine was investigated. Experiments were carried out in a constant volume vessel under conditions similar to the real engine condition using a single hole nozzle. Biodiesel fuels from two sources namely; palm oil (BDFp) and cooked oil (BDFc) with the commercial JIS#2diesel fuel were utilized in this research. The OH chemiluminescence technique was used to determine the ignition and the lift-off length of the combusting flame. The natural luminosity technique was applied to study the flame development and the two color pyrometry was applied for the soot formation processes. Ignition delay decreased as the injection pressure progressed from 100 to 300MPa. This was as a result of the enhanced mixing achieved at higher injection pressures.
Technical Paper

Basic Aspect of Combustion of CNG Incylinder Direct-Injection with Spark-Ignition

This paper presents basic combustion behavior of a compressed natural gas directly injected into a cylinder with spark-ignition. Experiments were conducted in a rapid-compression machine (RCM) with the cylinder bore of 80 mm, the stroke of 180 mm and the compression ratio of 10 at TDC. A CNG was injected through specially designed injectors which were installed at the side of combustion chamber with three modes, twin injectors in parallel, twin injectors in opposed and single injector. Combustion products were also measured with an infra-red gas analyzer. Direct photographs were taken with a high-speed video for observation. Effect of fuel injection timing was examined at constant spark timing together with the influence of injection mode. Results show several beneficial combustion characteristics of direct injection combustion using CNG. Combining with the results of combustion products and photographic observation, the combustion mechanism is discussed.