Search Results

A versatile liquid dosing device along with its metering theory, which can be applied to both SCR dosing system and DPF regeneration system of IC engine after-treatment system, is presented in this paper. The device is composed of a solenoid driven plunger pump, a nozzle and a pressure tube, and is pump-end controlled by PWM signals. Both electrically resistive and conductive liquids including DEF for SCR system, fuel for DPF regeneration, and gasoline for spark ignition engine, can be dispensed quantitatively with this device. A metering theory determining the liquid discharged per injection is developed by studying the system using a physical-mathematical model. The study shows that the liquid discharge can be well correlated with a measurable variable T3, which is associated with the net output energy. Experimental investigations verified that the metering results were independent of the state changes.

In-cylinder flow characteristics in a four-stroke diesel engine were studied experimentally by instantaneous measurements of swirl and squish flow velocity distribution with particle image velocimetry (PIV). The triple-exposed PIV films were interrogated on a self-made system to get the velocity distribution. The measured velocities were analyzed by spatially high-pass and low-pass filtering techniques. Vorticity distributions were also calculated using the measured data. As results, vortex structure of the flow field was clearly visualized. Spatially averaged in-cylinder flow energy was found decaying at high rate but the less-scaled flow components at much lower rate. Clearly visualized squish and reverse squish movements around the top dead center (TDC) during the compression stroke were found strongly affecting the swirl flow field. making the in-bowl flow energy increased.

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.

In this paper, the application of Shallow Water Modeling (SWM) method to simulate the compressible viscous plane flow for studying squish movement in combustion chambers of diesel engines is reported. The principle and analogue criteria of this method are discussed and derived. Using this method combined with visualization technique, the flow patterns were obtained and compared with those obtained by other methods. T1te results show that the SWM method is adequate and favorable for such investigation.

The Lambert-Beer's coefficient K was measured in a wide range of temperatures (400-1200K) and pressures (2-8.2 MPa) in this paper. Based on the measured MAP of K and principle of energy conservation in the sprays mass and transfer, a quantitative presentation of equivalence ratio and temperature in vapor phase sprays at diesel engine like conditions was put forward. The experimental range of temperatures was 800-1100K and 20-100 kg/m₃ for density. It was found that the maximum equivalence ratio of vapor phase spray remained fairly constant at about 3.0 and the maximum equivalence ratio appearance earlier as the ambient density increased, while the ambient temperature in the constant volume vessel was set at 800K. The maximum equivalence ratio of vapor phase spray increased from about 3.0 to about 3.7 as ambient temperature increased from 800 to 1100K.

The spark ignition-controlled auto-ignition (SI-CAI) hybrid combustion is promising in achieving smooth transition between SI and CAI combustion but, it is limited by the combustion cyclic-variation at late combustion phasing to avoid too high pressure rise rate (PRR). In this paper, to stabilize the combustion and reduce PRR, the in-cylinder fuel-stratification strategy is investigated in a gasoline engine, equipped with port fuel injection combined with single pulse direct injection (PFI-DI). Experimental results confirm the benefits of employing PFI-DI in comparison with PFI and single-pulse DI strategy. The influence of DI timing (Start of injection, SOI) on the combustion process is found to be quite complicated, in terms of combustion phasing, combustion stability, PRR and thermal efficiency. It makes the optimal-SOI calibration time-intensive, since complex trade-off between PRR and thermal efficiency is needed.

SI-CAI hybrid combustion, also known as spark-assisted compression ignition (SACI), is a promising concept to extend the operating range of CAI (Controlled Auto-Ignition) and achieve the smooth transition between spark ignition (SI) and CAI in the gasoline engine. In order to stabilize the hybrid combustion process, the port fuel injection (PFI) combined with gasoline direct injection (GDI) strategy is proposed in this study to form the in-cylinder fuel stratification to enhance the early flame propagation process and control the auto-ignition combustion process. The effect of bowl piston shapes and fuel injection strategies on the fuel stratification characteristics is investigated in detail using three-dimensional computational fluid dynamics (3-D CFD) simulations. Three bowl piston shapes with different bowl diameters and depths were designed and analyzed as well as the original flat piston in a single cylinder PFI/GDI gasoline engine.

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.

A numerical simulation was performed to investigate the pilot ignited natural gas combustion process in a direct injection natural gas engine. Various mixture distribution characteristics were compared in terms of the evolution of mixture equivalent ratio distributions and mixture concentration stratifications around top dead center (TDC). Based on above, the pilot injections were specially designed to investigate ignition core formation and its effects on natural gas combustion process. The result shows that pilot ignition sites have great impacts on pilot fuel ignition process and natural gas combustion process. The pilot ignition site on the region with rich NG/Air mixture is disadvantageous to the pilot fuel ignition due to a lack of oxygen, which is not beneficial to ignition core formation.

Using a Laser Doppler Velocimetry with Burst Spectrum Analyzer (LDV-BSA), droplet velocities of a diesel fuel spray under a pressure higher than 100 MPa were measured at different points within the spray profile. Results show that although the mean velocity distribution at the sampling plane is rather uniform, the number-based droplet velocity distributions of two sampling points at the same plane are different. The conclusions agree with theoretical predictions through maximum entropy principle qualitatively.

This paper presents a method to identify the radiation noise source of diesel engine based on a Cepstrum Analysis (CA) and Analytic Hierarchy Process (AHP). Through measuring noise and surface vibrations of a diesel engine, cepstrum analysis is applied to the measured signals. In an investigation of the radiation noise source, the hierarchy tree and judgment matrix are given. Through identification, the main noise source is found. The results show that the left body contributes maximally to non-harmonic spectral characteristics of noise. Therefore, in order to reduce engine vibration and noise effectively, we should optimize and improve left body. In addition, optimizing and improving gear chamber casing, oil pan, inlet pan and valve chamber cover can decrease harmonic vibration and noise of engine.

Droplet velocities in a diesel fuel spray before and after impinging on a wall as well as air movement around the spray are measured at room temperature and pressure. The range of fuel injection pressure is from 101 MPa to 139 MPa. The diagnostic equipment is a Laser Doppler Velocimetry with Burst Spectrum Analyzer (LDV-BSA).The results show that the droplet velocities of such a high pressure diesel fuel spray spread in a wide range (about 0-250m/s), so it is necessary to use the ensemble average for describing the velocity variation with time and space. After injection, the velocity reaches its peak value rapidly then attenuates gradually. When the spray impinges on the wall, the average velocity of the rebounded droplets is obviously reduced and the rebounded angle of most droplets is smaller than 30 degree when the incident angle is 70 degree. In the near field zone, the air entrainment in spray jet appears to be lower than that in gaseous one.

Natural gas is regarded as one of the most potential alternative fuels of engines because of its fruitful storage, good obtainable resources, and high octane value, etc. Compared with port fuel injection (PFI), Gasoline direct injection (GDI) has many advantages on volumetric efficiency improvement, lean-burning, emissions control, etc. A set of measuring and data acquisition system on CNG direct injection spark-ignited engines and the CNG multi-direct injection system are developed in this paper. Based on different injection modes of CNG single DI and compound DI (main injection and auxiliary-Injection), the investigations on combustion process of CNG DI engines has been conducted by the factors of in-cylinder mixture formation, air/fuel ratio, and injection timing, etc. Meanwhile, the three-dimension simulation on mixture formation and combustion principle of low-pressure CNG compound direct injection engines has also been researched.

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) technology is promising to reduce engine exhaust emissions and fuel consumption in gasoline engine. However, it is still confronted with the problem of its limited operation range. High load is limited by the tradeoff between the quantity of working charge and dilution charge. Low load is limited by the high residual gas fraction and low temperature in the cylinder. One of the highlights of HCCI combustion research at present is to expand the low load limit of HCCI combustion by developing HCCI idle operation. The main obstacle in developing HCCI idle combustion is too high residual gas fraction and low temperature to misfire in cylinder. This paper relates to a method for achieving the appropriate environment for auto-ignition at idle and the optimal tradeoff between the combustion stability and fuel consumption by employing EIVO valve strategy with an equivalent air-fuel ratio.

It is found that a thin and rich mixture layer on a wall is formed after impingement of a gas jet of fuel on the wall. The measured thickness of the mixture layer is about 2 mm. and its dispersion rate after the end of injection is much lower, compared to that of a space gas jet. This phenomenon in a small D.I. diesel engine is known as “wall wetting” or “wall fuel accumulation” which has an important influence on engine fuel consumption and emissions. This paper presents a technique for enhancing the near wall mixing of an impinging jet by means of a bump on the wall. The development of a wall jet formed after an impingement of a gas jet has been investigated by simultaneously measuring the near wall velocity and concentration distribution. It has been found that a wall jet is stripped off the wall and ejected as a secondary jet when the wall jet encounters a bump of the wall.

The RCS (Rankine cycle system) used to recover the exhaust gas energy from internal combustion engines has been regarded as one of the most promising ways to achieve higher efficiency. However, it is a big challenge to keep the RCS still in good performance under variable driving cycle. This paper aims at revealing the reasons resulting in the low efficiency under driving cycle, comparing to that under steady-state condition. The dynamic operating process of the RCS under driving cycle is analyzed, and then the RCS applied on an 11.6L heavy duty diesel engine is modeled. Based on that, the dynamic performance of the RCS under an actual driving cycle is discussed. The results indicate that the average efficiency under a piece of Tianjin bus driving cycle is as low as 3.63%, which is less than half of that (7.77%) under the rated point (1300rpm and 50%load). The reasons leading to the low efficiency under driving cycle is interpreted from three aspects.

Chemical reaction kinetics plays an important role in homogeneous charge compression ignition (HCCI) combustion. In order to control the combustion process, the underlying mechanism of auto-ignition must be explored, especially for the HCCI combustion using negative valve overlap (NVO) strategy, in which the residual gas affects the auto-ignition of next cycle remarkably. In this research, experimental research was carried out in a single cylinder gasoline engine equipped with an in-cylinder sampling system which mainly consists of a special spark plug, a sampling tube and a high-speed electromagnetic valve. In-cylinder charge was sampled at compression stroke and analyzed by FTIR with two types of fuel injection strategy, such as port fuel injection (PFI) solely and port fuel injection combined with injection during negative valve overlap (PFI & NVO-Injection).

Engine experiments and CFD modeling studies have been carried out and shown that high density-low temperature combustion (H Density-LTC) has the potential of realizing high thermal efficiency and very low engine-out emissions at high and full engine loads. Parametric studies were conducted to explore the mechanism of formation of pollutants in high charge density in this paper. It was found that high charge density was normally favorable to spray atomization, evaporation and fuel/air mixing throughout the entire combustion process, but there was a turning value of charge density above which the improvement of thermal efficiency was reduced. The conversion of CO to CO₂ was accelerated and CO emission was decreased with increasing charge density, which was also proved to be beneficial to re-oxidation of soot formed. The oxygen concentration brings a conflict effect to NOx emissions and exhaust soot. The high density combustion relieved the conflict effect of oxygen concentration.