An experimental study on the effects of impingement-walls on the spray and combustion characteristics of SIDI CNG

Compressed natural gas (CNG) is regarded as one of the most promising alternative fuels, and maybe the cleanest fuel for the sparkignition (SI) engine. In the SI engine, direct injection (DI) technology can significantly increase the engine volumetric efficiency and decrease the need of throttle valve. During low load and speed conditions, DI allows engine operation with the stratified charge, and the use of extremely lean fuel-air mixture enables relatively higher combustion efficiency. In this study, a combustion chamber with a visualization system is designed. The spray development and combustion propagation processes SIDI CNG were digital recorded. It was found that high injection pressure reduced the ignition probability significantly because of quenching of flame kernel. To improve the ignition probability, three kinds of impingement-walls were designed to help the mixture preparation. It was found that the CNG-air mixture can be easily formed after spray-wall impingement and the ignition probability was also improved. The results of this study can contribute important data for the design and optimization of spark-ignition direct injection (SIDI) CNG engine.     

Optical investigation of the fuel injector influence in a PFI spark ignition engine for two-wheel vehicles

This paper describes the results obtained in a port fuel injection spark-ignition (PFI SI) engine by optical diagnostics during the fuel injection and the combustion process. A research optical engine was equipped with the fuel injection system, the head and the exhaust device of a commercial 250 cc engine for scooters and small motorcycles. Two injectors were tested: standard 3-hole injector that equipped the real reference engine and a 12-hole injector. The intake manifold was modified to allow the visualization of the fuel injection using an endoscopic system coupled with CCD camera. Size and number of the fuel droplets were evaluated through an image processing procedure. The cycle resolved visualization and chemiluminescence allowed to follow the combustion process from the spark ignition to the exhaust phase. All the optical data were correlated with engine parameters and exhaust emissions. The effect of the fuel injector type on deposits formed by fuel accumulation and dripping on the intake valves steams and seats was investigated. In particular, the evolution of diffusion-controlled flames due to the fuel deposits burning was analyzed. These flames were principally located near the intake valves, and they persisted well after the normal combustion event. The consequences were the formation and emission of soot and unburned hydrocarbons. The multi-hole injector helped reducing wall wetting and deposit formation so that the emission characteristic can be improved. The use of 12-hole injector allowed a more homogeneous distribution for a lower time of fuel droplets in the intake manifold than the 3-hole injector. This study also investigated the detailed physical/chemical phenomena to figure out reasons for the improvement using optical measurements.     

预燃室射流点火对汽油机性能影响研究

通过试验手段对比分析了预燃室射流点火模式及火花塞点火模式 （SI）对燃烧性能的影响,结果表明:SI点火模式的发动机受高负荷爆震的限制,仅在中等负荷达到最佳的油耗率和热效率。压缩比（CR）的增加仅在中小负荷对油耗率和热效率有改善效果;相比于SI点火模式,预燃室射流点火模式可实现更快的燃烧速度和火焰传播速度,对SI发动机的爆震有较好的抑制效果,在中等负荷具有更低的油耗率和更高的热效率,但在低负荷及高负荷阶段,油耗率和热效率恶化;采用预燃室射流点火模式,能有效增加缸内燃烧速率,减轻CA50推迟对油耗率恶化的效果,通过提高压缩比实现降低油耗率的潜力和效果更好。     

Analysis of combustion and flame propagation characteristics of LPG and Gasoline fuels by laser deflection method

This work is to investigate the combustion characteristics and flame propagation of the LPG (liquified petroleum gas) and gasoline fuel. In order to characterize the combustion processes of the fuels, the flame propagation and combustion characteristics were investigated by using a constant volume combustion chamber. The flame propagation of both LPG and gasoline fuels was investigated by the laser deflection method and the high-speed Schlieren photography. The result of laser deflection method show that the error of measured flame propagation speed by laser method is less than5% compared with the result of high-speed camera. The flame propagation speed of the fuel is increased with the decrease of initial pressure and the increase of initial temperature in the constant volume chamber. The results also show that the equivalence ratio has a great effect on the flame speed, combustion pressure and the combustion duration of the fuel-air mixture.     

Performance and emission characteristics of a low heat rejection spark ignited engine fuelled with E20

In internal combustion engines, the concept of low heat rejection (LHR) using thermal barrier coating on the surface of combustion chamber is gaining attention. Thermal barrier coating reduces the heat transfer to the cooling system, protects engine components from peak heat flux and fluctuating temperature produced during combustion and improves the performance of the engine. Information in the literature is plentiful for LHR diesel engine and only few studies exist on LHR spark ignited engine. The application of thermal barrier coating in spark ignited engine is limited by pre-ignition and knocking due to elevated combustion chamber temperature. A spark ignited engine with moderate insulation on the combustion chamber and higher octane fuel can overcome this difficulty. The objective of the present experimental study is to quantify the changes in performance and emission characteristics brought by partial thermal insulation on the combustion chamber of a four stroke spark ignited engine fueled with E20 blend. Partial thermal insulation was created by coating 0.3 mm thick Alumina (Al₂O₃) on the cylinder head, inlet and exhaust valves. The changes are quantified with respect to unmodified engine fueled with gasoline. The combustion parameters such as flame development and rapid burn duration are also estimated and compared. The results indicate that partially insulated SI engine when fueled with E20 improves performance and reduces emission. A maximum of 48% reduction in THC and 50% reduction in CO emission at part load was achieved.

     

Experimental investigation on the effect of charge temperature on ethanol fueled HCCI combustion engine

In this investigation, an attempt has been made to study by varying the charge temperature on the ethanol fueled Homogeneous charge compression ignition (HCCI) combustion engine. Ethanol was injected into the intake manifold by using port fuel injection technique while the intake air was heated for achieving stable HCCI operation. The effect of intake air temperature on the combustion, performance, and emissions of the ethanol HCCI operation was compared with the standard diesel operation and presented. The results indicate that the intake air temperature has a significant impact on in-cylinder pressure, ringing intensity, combustion efficiency, thermal efficiency and emissions. At 170°C, the maximum value of combustion efficiency and brake thermal efficiency of ethanol are found to be 98.2% and 43%, respectively. The NO emission is found to be below 11 ppm while the smoke emission is negligible. However, the UHC and CO emissions are higher for the HCCI operation.

     

基于热力学模型的液化石油气发动机 燃烧放热及排放分析

通过燃用汽油及液化石油气的对比试验得出了两种燃料的对比燃烧特性,从而在燃烧机理上分析了其燃烧及排放特性。结论表明以汽油机改装的LPG(液化石油气)发动机自身带有一些缺陷,但通过改装及调试是可以获得较理想的动力性并改善排放指标的。     

An investigation on effect of high pressure post injection on soot and NO emissions in a DI diesel engine

NO and Soot trade off is an important challenge for engineers in DI Diesel engines. This paper, introduces multiple injection as a strategy for simultaneous reduction of NO and Soot emissions on a DI diesel engine and also proposes a new concept of variable injection pressure and studies its effect on the engine emissions. To evaluate the benefits of multiple injection strategies and to reveal combustion mechanism, modified three dimensional CFD code KIVA-3V was developed. Results showed that using post injection with appropriate dwell between injection pulses has a great effect on simultaneous reduction of the emissions. Based on computational results, NO reduction formation mechanism in multiple injection strategy is as a single injection with retarded injection timing. It is shown that reduction in soot formation is because of the fact that in split fuel injection the soot, which is producing rich regions at the head of fuel spray, are not replenished by newly injected fuel in post injection pulse. Also increasing injection pressure in post injection will reduce the Soot emission dramatically while NO emission is in control for increase of fuel burning rate in post injection pulse.     

缸内直喷汽油机冷启动燃烧与排放光学试验研究

结合光学单缸机和激光诱导荧光测量技术对直喷汽油机冷怠速工况缸内油气混合与燃烧过程进行了可视化试验研究。试验采用了屋脊形透明缸套和双侧激光,利用统计图像评估方法得到了缸内混合气浓度和燃烧火焰分布图像,通过缸压传感器和燃烧分析仪对燃烧稳定性进行了分析,采用废气分析仪和光学传感器分别对碳氢和碳烟排放进行了分析评估。研究表明：燃烧稳定时燃油与缸套碰壁是碳氢排放产生的主要原因,碳烟排放则主要由活塞顶部燃油碰壁造成;适当推迟第二次喷油时刻有利于点火时刻火花塞附近稳定浓混合气的形成,继而提高燃烧稳定性,同时减少碳氢排放,过迟喷射会导致碳烟明显增加,过早喷射会造成缸内失火,碳氢排放增加。     

Feasibility and performance study of turpentine fueled DI diesel engine operated under HCCI combustion mode

In the present investigation a volatile fraction of Pinus resin called Turpentine has been experimented in a direct injection diesel engine under HCCI combustion mode. The engine chosen to experiment is a single cylinder DI diesel engine and modified in such a way to ignite Turpentine in a diesel engine under HCCI mode. As the Turpentine has a higher self ignition temperature the ignition of Turpentine in regular diesel engines with auto-ignition is not possible. Hence, suitable modification is made in the engine to ignite Turpentine in a diesel engine like diesel fuel. The modified engine has ECM controlled fuel spray and an air preheater in the suction side of the engine. The combined effort of adiabatic compression and supply of preheated air ignites turpentine by auto-ignition and its timing of ignition is precisely controlled by changing intake air temperature. This investigation revealed that the engine operated with turpentine performed well with little loss of brake thermal efficiency. And, emitted comparatively lower emissions such as NO_x and smoke and proved that the turpentine is a best suited fuel for HCCI operation.     

A mathematical model for the prediction of the injected mass diagram of a S.I. engine gas injector

A mathematical model of gaseous fuel solenoid injector for spark ignition engine has been realized and validated through experimental data. The gas injector was studied with particular reference to the complex needle motion during the opening and closing phases, which strongly affects the amount of fuel injected. As is known, in fact, when the injector nozzle is widely open, the mass flow depends only on the fluid pressure and temperature upstream the injector: this allows one to control the injected fuel mass acting on the “injection time” (the period during which the injector solenoid is energized). This makes the correlation between the injected fuel mass and the injection time linear, except for the lower injection times, where we experimentally observed strong nonlinearities. These nonlinearities arise by the injector outflow area variation caused by the needle bounces due to impacts during the opening and closing transients [1] and may seriously compromise the mixture quality control, thus increasing both fuel consumption and pollutant emissions, above all because the S.I. catalytic conversion system has a very low efficiency for non-stoichiometric mixtures. Moreover, in recent works [2, 3] we tested the simultaneous combustion of a gaseous fuel (compressed natural gas, CNG, or liquefied petroleum gas, LPG) and gasoline in a spark ignition engine obtaining great improvement both in engine efficiency and pollutant emissions with respect to pure gasoline operation mode; this third operating mode of bi-fuel engines, called “double fuel” combustion, requires small amounts of gaseous fuel, hence forcing the injectors to work in the non-monotonic zone of the injected mass diagram, where the control on air-fuel ratio is poor. Starting from these considerations we investigated the fuel injector dynamics with the aim to improve its performance in the low injection times range. The first part of this paper deals with the realization of a mathematical model for the prediction of both the needle motion and the injected mass for choked flow condition, while the second part presents the model calibration and validation, performed by means of experimental data obtained on the engine test bed of the internal combustion engine laboratory of the University of Palermo.     

Investigation of the effects of steam injection on the emissions and performance of a diesel engine using waste chicken oil methyl ester

The use of biodiesel-blended fuels in diesel engines improves the engine performance parameters and the partial recovery of incomplete combustion products, while also increasing the level of NOx emissions. In this study; biodiesel obtained through the transesterification of waste chicken frying oil was mixed with diesel fuel (90% diesel + 10% biodiesel-B10), and was then used as fuel in a direct injection diesel engine. To reduce the increased NOx emissions caused by the use of B10 fuel, the steam injection method (which is one of the NOx reduction methods) was applied. Steam was injected into the intake manifold at different ratios (5%-S5, 10%-S10 and 15%-S15) and at the time of the induction stroke with the aid of an electronically controlled system. Based on the study results, it was observed that steam injection into the engine using B10 fuel improved both the engine performance and the exhaust emission parameters. It was determined that the S15 steam injection ratio resulted in the best engine performance and emissions parameters. In comparison to STD fuel; the highest increase observed at the S15 steam injection ratio in the effective engine power was 2.2%, while the highest decrease in the specific fuel consumption was 3.4%, the highest increase in the effective efficiency was 3.5%, and the highest decrease in NOx emissions was 13.7%.

     

Pulsed illumination, closed circuit television system for real-time viewing of unsteady (> 1 micros) events

A pulsed illumination closed circuit television system is described whereby fast (times <33 ms), unsteady events can be observed in real time. A low-power helium-neon laser beam is modulated to send a short duration light pulse through the unsteady test medium. The light is refracted according to the instantaneous optical properties of the medium. The refracted light travels to a solid state television camera, known as a charge injection device (CID), in which the sensor array is charged within microseconds. The scanning of the charged array then follows, requiring the standard 33 ms for information transfer to video tape and a TV monitor. The image is thus formed during the laser pulse duration (which presently is 10 to 100 micros, but shorter duration pulses are possible with more powerful lasers), but no more than one image every 33 ms can be observed and recorded. Thus this method is particularly suited for the investigation of high frequency periodic events in which one can observe both a single image, or an ensemble average of as many as 100 images, occurring at corresponding times in different cycles. The reported applications include the recording of steady and transient propane torch flames, of the transient fuel injection process in a motored internal combustion engine, and of the propagation of a flame under firing conditions in the engine. In the shadowgraph and Schlieren modes the method is particularly suited for application to periodic combustion events such as those occurring in internal combustion engines. The method then presents the following advantages over high-speed filming (> 3000 pictures/s); real-time observation and recording of chamber events at any crankangle; real-time observation and recording of the effects of changes in the engine variables (speed, load, spark timing, injection pressure and duration, chamber swirl, etc.) on the combustion events; real-time observation and recording of ensemble averages and cycle-to-cycle variations. The technique also eliminates the delays and unknowns of film processing. Finally, the cost of this system is similar to that of a high-speed camera.     

Investigation of soot formation in a D.I. diesel engine by using laser induced scattering and laser induced incandescence

Soot has a great effect on the formation of PM (Paniculate Matter) in D.I. (Direct Injection) Diesel engines. Soot in diesel flame is formed by incomplete combustion when the fuel atomization and mixture formation were poor. Therefore, the understanding of soot formation in a D.I. diesel engine is mandatory to reduce PM in exhaust gas. To investigate soot formation in diesel combustion, various measurements have been performed with laser diagnostics. In this study, the relative soot diameter and the relative number density in a D.I. engine was measured by using LIS (Laser Induced Scattering) and LII (Laser Induced Incandescence) methods simultaneously which are planar imaging techniques. And a visualization D.I. diesel engine was used to introduce a laser beam into the combustion chamber and investigate the diffusion flame characteristics. To find the optimal condition that reduces soot formation in diesel combustion, various injection timing and the swirl flow in the cylinder using the SCV (Swirl Control Valve) were applied. From this experiment, the effects of injection timing and swirl on soot formation were established. Effective reduction of soot formation is possible through the control of these two factors.     

Effect of spark plug protrusion on the performance and emission characteristics of an engine fueled by hydrogen-natural gas blends

Mixtures of hydrogen and natural gas are promising for improving efficiency and reducing harmful emissions in spark ignition engines, since limits of flammability can be extended while stable combustion is secured. In this research, the combustion characteristics of long electrode spark plugs were evaluated in a hydrogen blended with natural gas (HCNG) engine. Decreases in the flame propagation distance through the use of spark plugs can lead to increased burning rates and further improvement of fuel economy in HCNG engines. An 11-liter heavy duty lean burn engine was employed and performance characteristics including emissions were assessed according to the spark timing of the minimum advance for best torque (MBT) for each operating condition. Retarded MBT spark advance timing with long electrode spark plugs due to increased burning speed supported increases in engine efficiency and reductions of nitrogen oxide (NO_x) emissions. The lower positions of initial flame kernels due to the use of long electrode spark plugs were preferable to improvements of cyclic variability due to reduced flame front quenching, and carbon monoxide (CO) emissions at the flammability limit were also improved.     

Effects of different piezo-acting mechanism on two-stage fuel injection and CI combustion in a CRDi engine

In this study, the effects of two piezo injectors operated by different mechanisms on multi-injection and Compression ignition (CI) combustion were investigated. High-pressure injectors for CI engines are divided into two categories according to the actuator: Solenoid and piezo injectors. It is commonly known that both injectors have a hydraulic circuit for fuel injection; thus, the performance of the injector is highly dependent on not only hydraulic characteristics such as volume of internal chambers and nozzle geometry, but also the actuation mechanism. Specially, the direct needle-Driven piezo injector (DPI) is introduced in this study and compared with the indirectacting Piezo injector (PI) to investigate the injection characteristics and influences on CI combustion performance by using spray visualization, injection rate measurement, and single cylinder diesel engine experiments, as well as numerical simulation for injection rate modeling of DPI. In the spray visualization experiment, a high-speed camera was used to examine spray tip penetration length and spray speed with respect to each injector. Also, in order to investigate injection rate information, which is a significantly dominant factor in combustion characteristics, the Bosch-tube method was adapted under the condition of a back pressure of 4.5 MPa, corresponding to engine motoring pressure. Also, a single-cylinder CRDi (Common-rail direct-injection) engine experiment was carried out to determine the effects of different piezo-acting mechanisms on two-stage fuel injection and CI combustion. From the key results obtained by this study, the direct needle-driven piezo injector has a faster SOI (Start of injection) and EOI (End of injection). In addition, the overall shape of the injection rate of DPI was narrow and the injection had a higher spray speed than that of PI. Also, DPI has a higher heat release rate and peak pressure, as verified by the engine experiment. In particular, it was found that DPI showed the possibility of combustion improvement when applying a pilot injection strategy.

     

Phenomenological combustion modeling of a direct injection diesel engine with in-cylinder flow effects

A cycle simulation program is developed and its predictions are compared with the test bed measurements of a direct injection (DI) diesel engine. It is based on the mass and energy conservation equations with phenomenological models for diesel combustion. Two modeling approaches for combustion have been tested; a multi-zone model by Hiroyasu et al (1976) and the other one coupled with an in-cylinder flow model. The results of the two combustion models are compared with the measured imep, pressure trace and NOx and soot emissions over a range of the engine loads and speeds. A parametric study is performed for the fuel injection timing and pressure, the swirl ratio, and the squish area. The calculation results agree with the measured data, and with intuitive understanding of the general operating characteristics of a DI diesel engine.     

热管理技术在散热器年会大放异彩

<正>中国汽车工业协会(如下简称中汽协)车用散热器委员会2014年会员大会于10月25日至26日在江苏无锡召开,本次会议由东风贝洱热系统有限公司总经理韩力主持,共有73个单位的120人参加。年会期间,组织了技术交流,有关专家进行了精彩的专题讲演,同时与会代表进行了深入的沟通和交流,并对协会工作提出了很多好的意见和建议。清华大学—广东大华发动机热管理联合试验室、广东大华仁盛科技集团技术研究院总工程师刘景平从热管理时代和散热器行业发展趋势方面做了精彩演讲。     

An experiment analysis of MILD combustion with liquid fuel spray in a combustion vessel

Mild combustion is characterized by its distinguished features, such as suppressed pollutant emission, homogeneous temperature distribution, reduced noise, and thermal stress. Recently, many studies have revealed the potential of MILD combustion in various power systems but most studies have been focused on gas phase fuel MILD combustion. Therefore, further study on MILD combustion using liquid fuel is needed for the application to a liquid-fueled gas turbine especially. In this work, we studied experimentally on the formation of liquid fuel MILD combustion under the condition of high dilution by burnt gas generated from a first premixed flame in two stages combustor which consists of the first premixed burner and secondary combustor. In particular, the effects of burnt gas velocity and oxygen level of burnt gas on the formation of liquid fuel MILD combustion were investigated. The results show that as the burnt gas velocity through the nozzle becomes higher, the color of flames was changed from yellow to pale blue and flames became very short. The OH radical measured by ICCD camera was uniformly distributed on the pale blue flame surface and its intensity was very low compared to conventional liquid diffusion flame. As burnt gas velocity is increased, local high-temperature region appeared to be diminished and the flame temperature became spatially uniform. And CO emission was sampled around 1 ppm and NOx emission was measured around 10 ppm under the overall equivalence ratio of 0.8 to 0.98 for 40 mm or less diameter of velocity control nozzle. This low NOx emission seems to be attributed to maintaining the average temperature in secondary combustor below the threshold temperature of thermal NOx formation. In view of the uniform temperature distribution, low OH radical intensity and low NOx emission data in the secondary combustor, formation of stable MILD combustion using kerosene liquid fuel could be verified at high burnt gas velocity.

     

Thermodynamic model for prediction of performance and emission characteristics of SI engine fuelled by gasoline and natural gas with experimental verification

In this study, a thermodynamic cycle simulation of a conventional four-stroke SI engine has been carried out to predict the engine performance and emissions. The first law of thermodynamics has been applied to determine in-cylinder temperature and pressure as a function of crank angle. The Newton-Raphson method was used for the numerical solution of the equations. The non-differential form of equations resulted in the simplicity and ease of the solution to predict the engine performance. Two-zone model for the combustion process simulation has been used and the mass burning rate was predicted by simulating spherical propagation of the flame front. Also, temperature dependence of specific heat capacity has been considered. The performance characteristics including power, indicated specific fuel consumption, and emissions concentration of SI engine using gasoline and CNG fuels have been determined by the model. The results of the present work have been evaluated using corresponding available experimental data of an existing SI engine running on both gasoline and CNG. It has been found that the simulated results show reasonable agreement with the experimental data. Finally, parametric studies have been carried out to evaluate the effects of equivalence ratio, compression ratio and spark timing on the engine performance characteristics in order to show the capability of the model to predict of engine operation.