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To improve the combustion and emission characteristics of the large-bore marine engines, the spray is usually designed as an inter-spray impingement to promote the fuel-air mixing process, which implies frequent droplet collisions. Properly describing the collision dynamics of liquid droplets has been of interest in the field of spray modeling for marine engine applications. In this context, this work attempts to develop an accurate and efficient methodology for modeling impinging sprays under engine-like conditions. Experimental validations in terms of spray penetration and morphology are initially carried out at different operating conditions considering the parametric variations of ambient temperature and pressure, where the measurements are performed on a large-scale constant volume chamber with two symmetrical injectors.

Computational fluid dynamics (CFD) modeling has many potentials for the design and calibration of modern and future engine concepts, including facilitating the exploration of operation conditions and casting light on the involved physical and chemical phenomena. As more attention is paid to the matching of different fuel types and combustion strategies, the use of detailed chemistry in characterizing auto-ignition, flame stabilization processes and the formation of pollutant emissions is becoming critical, yet computationally intensive. Therefore, there is much interest in using tabulated approaches to account for detailed chemistry with an affordable computational cost. In the present work, the tabulated flamelet progress variable approach (TFPV), based on flamelet assumptions, was investigated and validated by simulating constant-volume Diesel combustion with primary reference fuels - binary mixtures of n-heptane and iso-octane.

Applications of methanol and biodiesel in internal combustion engines have raised widespread concerns, but there is still huge scope for improvement in efficiency and emissions. The brand-new combustion mode, named as Intelligent Charge Compression Ignition (ICCI) combustion, was proposed with methanol-biodiesel dual fuel direct injection. In this paper, effects of injection parameters such as two-stage split-injections, injection timings, injection pressure and intake pressure on engine combustion and emissions were investigated at IMEP = 8, 10, and 12 bar. Results show that the indicated thermal efficiency up to 53.5% and the NOx emissions approaching to EURO VI standard can be obtained in ICCI combustion mode.

Developing advanced combustion mode has been the active area for high efficiency and ultra-low emissions of the next-generation internal combustion engines. In this paper, a series of experiments were conducted in a modified single-cylinder compression ignition engine for operating a brand-new combustion mode denoted as intelligent charge compression ignition (ICCI) mode. By using two common-rail systems, commercial gasoline and diesel were alternately directly injected into the cylinder through multi-injection strategies in the injection timing range of 50~320 °CA BTDC. Thus, the in-cylinder stratified condition can be flexibly and accurately adjusted in this unique combustion mode. The key injection parameters, such as gasoline injection timing and diesel split ratio, were investigated to explore their effects on engine combustion, emissions, and fuel consumption.

Multiple injection strategies are commonly used in conventional Diesel engines due to the flexibility for optimizing heat-release timing with a consequent improvement in fuel economy and engine-out emissions. This is also desirable in low-temperature combustion (LTC) engines since it offers the potential to reduce unburned hydrocarbon and CO emissions. To better utilize these benefits and find optimal calibrations of split injection strategies, it is imperative that the fundamental processes of multiple injection combustion are understood and computational fluid dynamics models accurately describe the flow dynamics and combustion characteristics between different injection events. To this end, this work is dedicated to the identification of suitable methodologies to predict the multiple injection combustion process.

Recently, all world countries facing the stringent emission regulations have been encouraged to explore the clean fuel. The diesel from indirect coal liquefaction (DICL) has been verified that can reduce the soot and NOx emissions of compression-ignition engine. However, the atomization characteristics of DICL are rarely studied. The aim of this work is to numerically analyze the inner nozzle flow and the atomization characteristics of the DICL and compare the global and local flow characteristics of the DICL with the NO.2 diesel (D2) at engine conditions. A surrogate fuel of the DICL (a mixture of 72.4% n-dodecane and 27.6% methylcyclohexane by mass) was built according to its components to simulate the atomization characteristics of the DICL under the high-temperature and high-pressure environment (non-reacting) by the Large Eddy Simulation (LES).

The purpose of present numerical study was to extend the operating range of alcohol (methanol and ethanol) fueled Homogeneous Charge Compression Ignition (HCCI) engine under low load conditions. Ignition of pure methanol and ethanol under HCCI mode of operation requires high intake temperatures and misfires at low loads are common in HCCI engines. Three methods have been adapted to optimize the use of methanol and ethanol for HCCI operation without increasing the intake temperature. First, blending methanol and ethanol with ignition improver, namely di-methyl ether (DME) and di-ethyl ether (DEE), was used to increase the cetane number and ignitability of premixed charge. Second, based on the blended fuels, the spark assistance was used to reduce required intake temperature for auto-ignition. Third, DME and DEE were directly injected to methanol and ethanol operated HCCI engine, in the form of Reactivity Controlled Compression Ignition (RCCI) combustion.

Recently, the shortage of fossil resources contributes to strict regulations of environmental protection. The research on the high efficiency and low emission of engines becomes an important direction all over the world. Technologies like high injection pressure, high levels of supercharging and higher levels of back pressure have come into application. Increasing the injection pressure and average cylinder pressure results in that parts of the spray can experience transcritical and supercritical regimes. In this paper, we established a surrogate fuel composed of n-Hexadecane, HMN and 1-Metylnaphthalene, to analyze the injection and atomization of diesel surrogate fuel with large eddy simulation (LES) in a cubic calculation region with high temperature and high pressure environment. The injection pressure was fixed to 150MPa, and the 900-K temperature and the 6-MPa pressure represented the ambient condition in constant volume vessel which is supercritical with respect to No.2 diesel.

Combustion instability often occurs inside the combustion chamber of aero engine. Fuel atomization and evaporation, one of the controlling processes of combustion rate, is an important mechanism of the combustion instability. To tackle combustion instability, it challenges a deep understanding of the underlying mechanism of fuel atomization and evaporation. In this paper, acoustic field was established to simulate the pressure oscillation. Transient spray images of ethanol and kerosene were recorded using high-speed camera. The obtained images were processed by MATLAB to extract and analyze the related data. Spatial fuel atomization characteristics was analytically examined by multi-threshold image method to analyze the effect of the high frequency acoustic field on the fuel break-up and disintegration. The results show that the half spray cone angle on the side with speaker is suppressed by the presence of the imposed acoustic field compared with the case without speaker.

In this paper, an experimental study has been conducted to study the effects of iso-alkanes blending in diesel on combustion and emission characters based on a modified single cylinder diesel engine. Iso-octane, iso-dodecane and 2,2,4,4,6,8,8-heptamethylnonane (HMN) were chosen as test iso-alkanes. The direct injection timing was kept at 7 oCA BTDC. The injection pressure was maintained at 120 MPa. The study found that iso-alkanes had strong effects on the heat release phase under low load. The effects were weakened gradually with the increase of loads. The peak value of heat release curves and the maximum pressure rising rate gradually increased with the increase of loads. Blending iso-alkanes resulted in the increase of CO emissions and decrease of HC emissions. NOx emissions also decrease under low loads. Under high loads, blending iso-alkanes reduced the soot emissions significantly.

An experimental study was conducted on the combustion and emissions characteristics of duel fuel sequential combustion (DFSC) mode on a single-cylinder engine, applying port injection of n-heptane combined with in-cylinder direct injection of commercial gasoline, ethanol and n-butyl alcohol, respectively. Three-stage combustion, which consists of low- and high-temperature combustion of premixed n-heptane and high temperature combustion of directly injected gasoline-like fuels were observed. The effects of the premixed ratio and overall heating values per cycle on the combustion characteristics and emissions were investigated. The experimental results show that: with the increasing of premixed ratio and overall heating values per-cycle, the ignition timing of the directly injected fuels advances and the maximum pressure and maximum mass-averaged temperature increase.

This article investigates the basic combustion parameters including start of ignition, combustion duration, and CO, UHC, and NOx emissions of HCCI combustion engines fueled with primary reference fuels and their mixtures. A single-cylinder HCCI combustion engine, which was converted from a four-cylinder high-speed diesel engine, was used to the tests. Two primary reference fuels, n-heptane and iso-octane, and their mixtures including RON25, RON50, RON75, and RON90 were evaluated. In addition, the effects of cooled EGR on the HCCI combustion and emissions were also studied. The experimental results shown that, in the first-stage combustion, with the increase of the research octane number, the start of ignition retards, the combustion duration shortens, and the pressure rising and the temperature rising during the first-stage combustion decrease. Furthermore, the cumulative heat release in the first stage is strongly dependent on the concentration of n-heptane in the mixtures.