Effect of various LPG supply systems on exhaust particle emission in spark-ignited combustion engine

The particle size distribution and particle number (PN) concentration emitted by internal combustion engine are a subject of significant environmental concern because of their adverse health effects and environmental impact. This subject has recently attracted the attention of the Particle Measurement Programme (PMP). In 2007, the UN-ECE GRPE PMP proposed a new method to measure particle emissions in the diluted exhaust of automotive engines and a regulation limit (<6.0×10¹¹ #/km, number of particles). The specific PN regulation of spark-ignited combustion engine will be regulated starting on September 1, 2014 (EURO 6). In this study, three types of LPG supply systems (a mixer system and a multi-point injection system with gas-phase or liquid-phase LPG fuel) were used for a comparison of the particulate emission characteristics, including the nano-sized particle number density. Each of the three LPG vehicles with various LPG injection systems contained a multi-cylinder engine with same displacement volumes of 2,000 cm³ and a three-way catalytic converter. The test fuel that was used in this study for the spark-ignited combustion engine was n-butane basis LPG fuel, which is primarily used for taxi vehicles in Korea. The characteristics of nano-particle size distribution and number concentration of particle sizes ranging from 20 to 1,000 nm (aerodynamic diameter) that were emitted from the three LPG vehicles with various LPG supply systems were investigated by using a condensation particle counter (CPC), which is recommended by the PMP under both the NEDC and FTP-75 test modes on a chassis dynamometer. The experimental results indicate that the PN emission characteristics that were obtained by the CPC system using the PMP procedure are sufficiently reliable compared to other regulated emissions. Additionally, the sources of PN emissions in ascending order of magnitude are as follows: mixer type, gas-phase LPG injection (LPGi) and liquid-phase LPG injection (LPLi) passenger vehicles. The liquid-phase LPG injection system produced relatively large particle sizes and number concentrations compared to the gaseous system, regardless of the vehicle driving cycle. This phenomenon can be explained by unburned micro-fuel droplets that were generated due to a relatively short homogeneous fuel-air mixture duration in the engine intake manifold. Also the particle number emissions from the LPG vehicle were influenced by the vehicle driving cycle.     

Study of diesel spray combustion and ignition using high-pressure fuel injection and a micro-hole nozzle with a rapid compression machine: improvement of combustion using low cetane number fuel

This study aimed to reduce NO_x and soot by creating a more homogeneous lean fuel distribution in a diesel spray using high-pressure fuel injection and a micro-hole nozzle. This injection system shortened the ignition delay, but a homogeneous lean fuel distribution in the diesel spray was not achieved. Using a lower cetane number fuel, the resulting longer ignition delay made a uniform, lean fuel distribution in the diesel spray possible with this injection system. Ignition and combustion were analyzed by the combustion chamber pressure history, and flame temperatures and KL values were analyzed by the two-color method.     

Experimental investigation and comparison of nanoparticle emission characteristics in light-duty vehicles for two different fuels

In recent years, particle number emissions rather than particulate mass emissions in automotive engines have become the subject with controversial discussions. Recent results from studies of health effects imply that it is possible that particulate mass does not properly correlate with the variety of health effects attributed to engine exhaust. The concern is now focusing on nano-sized particles emitted from I. C. engines. In this study, particulate mass and particle number concentration emitted from light-duty vehicles were investigated for a better understanding of the characteristics of the engine PM from different types of fuels, such as gasoline and diesel fuel. Engine nano-particle mass and size distributions of four test vehicles were measured by a condensation particle counter system, which is recommended by the particle measurement program in Europe (PMP), at the end of a dilution tunnel along a NEDC test mode on a chassis dynamometer. We found that particle number concentrations of diesel passenger vehicles with DPF system are lower than gasoline passenger vehicles, but PM mass has some similar values. However, in diesel vehicles with DPF system, PM mass and particle number concentrations were greatly influenced by PM regeneration. Particle emissions in light-duty vehicles emitted about 90% at the ECE15 cycle in NEDC test mode, regardless of vehicle fuel type. Particle emissions at the early cold condition of engine were highly emitted in the test mode.     

Morphological Change and Number-Size Distributions of Particulate Matter (PM) from a Diesel Generator Operated with Wood Pyrolysis Oil-Butanol Blended Fuel

This report details our experimental study investigating particulate matter (PM) emissions from a diesel generator fueled with wood pyrolysis oil (WPO)–butanol blended fuel for electricity generation. Particle number-size distributions and PM mass concentrations from diesel, n-butanol, and WPO-butanol blended fuels were investigated via aerosol measurements using a fast mobility particle sizer and an aerosol monitor with three generator outputs (0, 3.3, and 6.6 kWe). For the n-butanol and WPO-blended fuels, the total number concentrations of exhaust particles were higher than that of conventional diesel combustion; however, the PM mass was observed to be nearly zero for all the engine operating conditions due to the higher number concentration in the nuclei mode. The morphology of the exhaust particles was investigated by analyzing transmission electron microscopy (TEM) micrographs. The morphology of the particles was drastically changed according to the test fuels and engine loads. Two types of particles were observed, including soot and coke shaped particles. These results were directly related to the immaturity of incipient soot particles due to the different physical properties and chemical compositions of the fuels.     

Evaporating spray and flame distributions in the combustion chamber of a direct injection diesel engine

The characteristics of an evaporating diesel spray and the flame distribution in a combustion chamber of a D.I. diesel engine were investigated by using the laser light technique. The technique used was based on the extinctions of two wavelengths of ultraviolet and visible laser light. The transmitted laser light absorbed and scattered by the vapor, drops, soot and combustion products in the spray flame were separated into two wavelengths and captured. Further, the light radiated from the flame was imaged using the same measuring system by modifying the optical filters and the timing of the camera shutter.     

发动机燃用水乳化柴油的研究进展

综述了柴油机燃用水乳化柴油的燃烧与喷雾特性、动力性与经济性及排放特性,对比分析了发动机燃用水乳化柴油与普通柴油在性能上的差异及其原因,总结了水乳化柴油在柴油机上的应用优化方法。结果表明:与柴油相比,乳化柴油着火滞燃期延迟,燃烧持续期缩短,喷雾贯穿距变长或相差不大,火焰升起高度增加;燃用乳化柴油时动力性下降,但有效热效率较柴油升高;乳化柴油可以明显降低NOx和炭烟排放,但多数工况下HC和CO排放有所升高,低转速和中低负荷工况下尤为明显;燃用乳化柴油时颗粒物数量浓度增加,体积浓度减小,且对于醛类和噪声排放并没有改善作用;添加合适添加剂或结合发动机技术协同作用,可以针对性地改善乳化柴油的燃烧过程,进一步起到节能减排的效果。基于燃料稳定性与燃料理化特性综合优化目标的燃料设计,以及适用于乳化柴油的高压共轨柴油机燃烧组织参数优化是未来的研究方向。     

喷油器参数对柴油机燃烧特性影响的数值模拟

应用三维CFD模拟软件FIRE,对1台135柴油机的喷雾与燃烧过程进行了数值模拟。通过缸内流场分析和浓度分析,研究了喷孔数、喷孔锥角对燃烧过程的影响及对NOx和炭烟生成的影响。结果表明,喷孔数和喷孔锥角影响燃油的喷雾质量和油气混合质量,进而影响燃烧过程和排放物的生成;CFD模拟计算对优化喷油器参数,从而改进燃烧系统具有指导意义。     

Examination of PN emissions and size distributions of a hybrid city bus under real world urban driving conditions

Engine load-speed frequency map of a hybrid city bus, which operates on the routes of Sakarya Municipality, was compared with that of European Transient Cycle (ETC) and World Harmonized Transient Cycle (WHTC), which are the certification test cycles. It was observed that the hybrid city bus engine operates mostly at three main regions, which are idling (30% load and 750 rpm), motoring (0% load and 1200 rpm) and high load (80% load and 1800 rpm) conditions under real world urban driving conditions. However, engine load-speed frequency maps of the certification test cycles are significantly different and cannot represent the real world urban driving conditions of the hybrid city bus. Therefore, the Particle Number (PN) emissions of the hybrid city bus were investigated under real world urban driving conditions. The aims of work were to examine the effects of city bus hybridization on the particle emissions and develop PN emission factors. The PN concentrations and size distributions together with engine operating conditions were measured with a Particle Measurement Program (PMP) compliant system, which involves a condensation particle counter (CPC) and a particle sizer (EEPS). The measurements under real world urban driving conditions indicated that the emission factors of the hybrid city bus for the PN and Total PN are 8.99E+12 and 2.51E+13 #/kW-h, respectively. The PN size distribution measurements indicated that the particles up to approximately 20 nm are not very sensitive to changes in engine power and they are exist even during motoring conditions. But, the particles in the size range from 20 to 200 nm are very sensitive to sudden changes of the engine power.     

Instantaneous 2-D visualization of spray combustion and flame luminosity of GTL and GTL-biodiesel fuel blend under quiescent ambient conditions

An experimental study has been performed on spray combustion and two-dimensional soot concentration in diesel (ULSD), GTL and GTL-biodiesel fuel jets under high-pressure, high-temperature quiescent conditions. Instantaneous images of the fuel jets were obtained with a high-speed camera. It was confirmed that by blending GTL with 20% rapeseed biodiesel, certain fuel properties such as kinematic viscosity, density, surface tension, volatility, lower heating value and others may be designed and improved to be more like those of conventional diesel fuel but with considerable decrease in the amount of sulfur, PAH, cold filter plugging point, etc. The results showed that the spray tip penetration increased and the spray cone angle decreased when 20% biodiesel fuel was added to GTL fuel. Autoignition of the GTL-biodiesel blend occurred slightly earlier than that of diesel fuel. Experiments under high-pressure, high-temperature conditions showed that higher injection pressure induced a lower soot formation rate. The integrated flame luminosity, which serves as an indicator of soot concentration in the fuel jet, was slightly higher for the GTL-biodiesel blend than for pure GTL fuel due to the slightly higher sulfur content of pure biodiesel fuel.     

Evaluation of low-temperature diesel combustion regimes with n-Heptane fuel in a constant-volume chamber

The concept of Low Temperature Combustion (LTC) has been advancing rapidly because it may reduce emissions of NOx and soot simultaneously. Various LTC regimes that yield specific emissions have been investigated by a great number of experiments. To accelerate the evaluation of the spray combustion characteristics of LTC, to identify the soot formation threshold in LTC, and to implement the LTC concept in real diesel engines, LTC is modeled and simulated. However, since the physics of LTC is rather complex, it has been a challenge to precisely compute LTC regimes by applying the available diesel combustion models and considering all spatial and temporal characteristics as well as local properties of LTC. In this paper, LTC regimes in a constant-volume chamber with n-Heptane fuel were simulated using the ECFM3Z model implemented in a commercial STAR-CD code. The simulations were performed for different ambient gas O₂ concentrations, ambient gas temperatures and injection pressures. The simulation results showed very good agreement with available experimental data, including similar trends in autoignition and flame evolution. In the selected range of ambient temperatures and O₂ concentrations, soot and NOx emissions were simultaneously reduced.     

Experimental evaluation of SOF effects on EGR cooler fouling under various flow conditions

An experiment was conducted to characterize the effects of SOF on EGR cooler fouling. A removable singletube test rig combined with a soot generator was developed to represent an EGR cooler and diesel exhaust gas. The use of a soot generator, which controlled the size and concentration of soot particles, enabled independent variables to be completely controlled. Either n-dodecane or diesel lube oil as substitute SOFs were vaporized and injected into the test rig to evaluate their effects on the growth of PM deposits and the degradation performance of the EGR cooler. Coolant temperature, which seemed to be associated with SOF content, was chosen as an independent variable, and PM deposit mass per unit area and the effectiveness drop versus time increased as the coolant temperature decreased. The PM deposit mass per unit area and effectiveness drop had maximum values at a coolant temperature of 40°C for every n-dodecane injection rate. For substitute SOFs tested in this experiment, the deposit mass increased when either n-dodecane or diesel lube oil was injected, but the effect of lube oil was more significant. Diesel lube oil seemed to have a stronger effect on the reduction of thermal conductivity by filling pores in the deposits. When diesel lube oil was injected, the deposit mass per unit area increased 127% compared to dry soot without injection. The effectiveness drop after 10 hours increased only 12.5%.     

缸内喷雾燃烧CFD仿真模型校验

摘要：采用AVLFIRE软件,对某重型柴油发动机进行缸内喷雾燃烧过程仿真。利用内窥镜系统,获得缸内喷雾燃烧图像。通过CFD仿真结果与喷雾过程、燃烧火焰、碳烟浓度分布进行定性对比分析,校验了缸内喷雾燃烧CFD仿真模型的准确性。     

Nano-particle emission characteristics of European and Worldwide Harmonized test cycles for heavy-duty diesel engines

This study was conducted for the experimental comparison of particulate emission characteristics between the European and World-Harmonized test cycles for a heavy-duty diesel engine as part of the UN/ECE PMP ILCE of the Korea Particulate Measurement Program. To verify the particulate mass and particle number concentrations from various operating modes, ETC/ESC and WHTC/WHSC, were evaluated. Both will be enacted in Euro VI emission legislation. The real-time particle emissions from a Mercedes OM501 heavy-duty golden engine with a catalyst based uncoated golden DPF were measured with CPC and DMS during daily test protocol. Real-time particle formation of the transient cycles ETC and WHTC were strongly correlated with engine operating conditions and after-treatment device temperature. The higher particle number concentration during the ESC #7 to #10 mode was ascribed to passive DPF regeneration and the thermal release of low volatile particles at high exhaust temperature conditions. The detailed average particle number concentration equipped for golden DPF reached approximately 4.783E+11 #/kWh (weighted WHTC), 6.087E+10 #/kWh (WHSC), 4.596E+10 #/kWh (ETC), and 3.389E+12 #/kWh (ESC). Particle masses ranged from 0.0011 g/kWh (WHSC) to 0.0031 g/kWh (ESC). The particle number concentration and mass reduction of DPF reached about 99%, except for an ESC with a reduction of 95%.     

柴油机DOC+CDPF系统的过滤和再生性能试验研究

基于氧化催化转化器(DOC)+催化型颗粒捕集器(CDPF)系统开展了发动机台架试验,对比系统前后的颗粒物粒径分布,获得了系统的过滤效率,同时也测量了该系统在各稳态工况下的再生效率.研究结果表明:该系统对颗粒物的过滤效率在发动机的各个工况均能达到95%以上;系统前的颗粒物数量浓度呈单峰分布,主要为核模态;系统后颗粒物数量浓度呈双峰分布,峰值分别在10 nm和150 nm左右,且10 nm左右波峰峰值最大;再生效率随着再生温度的升高呈上升趋势,测试系统的起燃温度在250℃以下;再生效率均随着再生时间的增加而增加,但在再生后期明显变缓;在较高的再生温度时,颗粒担载量增大将有利于提高再生速率.     

高压共轨柴油机燃烧与排放模型的研究

利用高速闪光摄影技术,对高压喷射喷雾体空间发展规律进行了试验分析,提出了一个计算高压喷射喷雾体发展的数学公式;在正确描述高压燃油喷雾的基础上,建立了一个能预测高压共轨柴油机性能和排放的准维燃烧模型,此模型改进了燃油喷射模型及碳烟的生成与氧化模型,考虑到燃烧区的区间传热和缸内工质的对流辐射传热,对一台高压共轨柴油机进行了仿真计算。计算与试验结果对比分析表明,改进后的燃烧与排放模型能较好地反映缸内各区的燃烧与排放情况。     

柴油掺混二甲醚喷雾粒子尺寸分布特性试验研究

为确定二甲醚掺入柴油后对燃料雾化性能的改善效果,利用阴影成像与数字图像处理技术,对不同掺混比、喷射压力以及喷孔直径等条件下的二甲醚-柴油混合燃料喷雾粒子尺寸分布特性进行了对比试验研究.结果发现:由于柴油中二甲醚的闪急沸腾作用,随着二甲醚掺混比的增加,混合燃料粒子尺寸分布曲线整体向小颗粒方向偏移,较大粒子数目较柴油明显减少,有助于降低发动机炭烟排放;喷孔直径、喷射压力等喷射参数对混合燃料雾化粒子分布有较大影响,减小喷孔直径使燃油粒子更加细化,降低喷射压力则使混合燃料雾化效果有变差的趋势.     

Nanoparticle emission characteristics and reduction strategies by boost pressure control and injection strategies in a passenger diesel engine

This research attempted to analyze nanoparticles and other harmful exhaust emissions in accordance with injection strategies and air-fuel ratio (AFR) changes for small diesel engines. The emission characteristics were analyzed in the medium-speed condition, which is the main driving range of a diesel engine. In the case of particulate matter (PM), the number of particles was measured, analyzed, and compared to identify the correlation and emission characteristics of nanoparticles by using a dilution device and condensation particle counter (CPC), which are international standards for particle measurement recommended by the Particulate Measurement Programme (PMP). The engine torque tended to be reduced as pilot injections were added, and the torque was increased by the increased boost pressure, but reduced by the exhaust pressure increase in a part of the low-load range. The number of nanoparticles was not influenced greatly by the change in AFR, but the reduction effect on the PM weight was great depending on the boost pressure increase. In addition, the number of nanoparticles tended to increase as the fuel injection timing became closer to TDC in all conditions, and its difference became larger with an increase in AFR. In addition, in the case of the pilot injection, nanoparticle emission showed similar characteristics depending on the main injection timing, but it was increased by advanced injection timing when performing the main injection only, and the number of the nanoparticles increased as pilot injections were added. Last, the optimal conditions for EMS calibration were analyzed by selecting the conditions of torque reduction and NOx increase within 5 % from all of the engine operating conditions; optimized conditions are presented.     

Numerical investigation of a DI diesel spray flame using a detailed chemical reaction mechanism

Emission standards have grown increasingly stricter, consequently triggering greater interest in issues surrounding environmental pollution. In particular, soot and NOx released from DI diesel vehicles is considered to be the main source of air pollution in urban environments. However, the mechanics of fuel spray formation and the influence of the operating parameters on the resulting spray flame are not yet fully understood. In this study, the original KIVA code was modified to incorporate a detailed chemical reaction mechanism involving various species and multiple reaction steps to better understand the spray characteristics. n-Heptane, C₇H₁₆, was used as the representative fuel for diesel fuel, and the reaction mechanism for this fuel was composed of 66 species and 274 elementary reaction steps. The accuracy of the predicted results was demonstrated primarily by a comparison with experimental results. The numerical prediction of a specific operating condition for the parametric investigation correlates well with the experimental results.     

Exhaust nanoparticle emissions from internal combustion engines: A review

This paper reviews the particle emissions formed during the combustion process in spark ignition and diesel engine. Proposed legislation in Europe and California will impose a particle number requirement for GDI (gasoline direct injection) vehicles and will introduce the Euro 6 and LEV-III emission standards. More careful optimization for reducing particulate emission on engine hardware, fuel system, and control strategy to reduce particulate emissions will be required during cold start and warm-up phases. Because The diesel combustion inherently produces significant amounts of PM as a result of incomplete combustion around individual fuel droplets in the combustion zone, much attention has been paid to reducing particle emissions through electronic engine control, high pressure injection systems, combustion chamber design, and exhaust after-treatment technologies. In this paper, recent research and development trends to reduce the particle emissions from internal combustion engines are summarized, with a focus on PMP activity in EU, CARB and SAE papers and including both state-of-the-art light-duty vehicles and heavy-duty engines.     

柴油机三级串联微粒收集消声装置的研制

介绍了基于离心静电技术的柴油机三级串联微粒收集消声装置,该装置利用旋转气流产生的离心力和静电装置产生的电场将碳粒从柴油机废气中分离,并通过红外加热板将碳粒加热使其燃烧。设计了离心静电碳烟微粒收集装置、碳烟微粒燃烧再生装置和碳烟微粒燃烧控制装置,并对柴油机三级串联微粒收集消声装置进行了试验验证,结果表明,柴油机废气碳烟的净化和消声同时达到满意的效果。