Development of engine control using the in-cylinder pressure signal in a high speed direct injection diesel engine

Emission regulations are becoming more stringent and remain a principal issue for vehicle manufacturers. Many engine subsystems and control technologies have been introduced to meet the demands of these regulations. For diesel engines, combustion control is one of the most effective approaches for reducing not only engine exhaust emissions but also cylinder-by-cylinder variation. However, the high cost of pressure sensors and the complex engine head design for additional equipment present difficulties for manufacturers. In this paper, cylinder pressure-based engine control logic is introduced for a multi-cylinder high speed direct injection (HSDI) diesel engine. The time for 50% of the mass fraction to be burned (MFB50) and the IMEP are valuable for determining the combustion status. These two in-cylinder quantities are measured and applied to the engine control logic. Fuel injection timing is controlled to adjust the operating MFB50 to the target MFB50 using PID control logic, and the fuel injection quantity is controlled to adjust the measured IMEP to the desired IMEP. The control logic is demonstrated at steady state and during transient conditions and is applied to an NEDC mode test.     

Development of hydrogen-compressed natural gas blend engine for heavy duty vehicles

Natural gas fuel, as an alternative energy source of transportation, has been used widely since it has an advantage of low emission levels. However, new technologies are required in order to meet the reinforced emission regulations. For this purpose, research into the development of hydrogen-compressed natural gas (HCNG) blend engine was carried out to evaluate its feasibility and emission characteristics. The Engine Research Department at the Korea Institute of Machinery and Materials carried out a large number of tests based on various parameter changes that could affect the performance and emission of HCNG engine in different operating conditions. An earlier stage of the research project focused on the lean combustion of a HCNG engine for heavy duty vehicles to meet the EURO-VI standards. An 11-L/6-cylinder CNG engine was used for the test. The effects of the excess air ratio change were assessed based on various content ratios of hydrogen in the natural gas fuel. In the later part of the HCNG research, a stoichiometric mixture operation was suggested to meet reinforced emission regulation without requiring a De-NOx system. Additionally, an exhaust gas recirculation (EGR) system was introduced for the purpose of improving thermal efficiency and durability. The optimal operating conditions were selected to achieve the best thermal efficiency to meet the required emission levels. In this paper, we demonstrate that a HCNG engine can achieve a significant decrease in NOx emissions, as compared to that of a CNG engine, while meeting the requirements of the EURO-VI standards during a transient mode cycle test. EGR can suppress the weakness of stoichiometric mixture combustion strategy, such as the deterioration of the durability and thermal efficiency, while the emission level can be lowered with the use of a three-way catalyst. The possibility of further reduction of emissions and CO2 with EGR was evaluated to access practical application of a HCNG engine in the field. From that evaluation, the HCNG engine with stoichiometric mixture operation for heavy duty vehicles was developed. The emission levels of HCNG engine were 50 % lower when compared to the EURO-VI standards with a greater than 10 % decrease in CO₂ compared to that of a natural gas engine.     

Flamelet combustion model for stratified EGR distribution in a diesel engine

Numerous research has been devoted to finding a method to simultaneously reduce NOx and soot emissions from diesel engines. In-cylinder EGR stratification is a technique that simultaneously reduces NOx and soot using a nonuniform EGR distribution in the combustion chamber. To study the potential of in-cylinder EGR stratification, a new combustion model is required that considers the non-uniform EGR distribution and the chemical kinetics. In this study, a new combustion model, the Flamelet for Stratified EGR (FSE) model, was developed to consider the non-uniform in-cylinder gas distribution based on chemical kinetics. The concept of the FSE model is based on using multiple flamelets with the multizone concept. To describe the non-uniform gas distribution, the combustion chamber is divided into several zones by oxygen concentration at the start of injection. Then, the flamelet equations are solved at the boundary of each zone. The final species mass fraction of each cell is calculated using linear interpolation between two results from the boundaries. In this paper, the FSE model was validated under in-cylinder EGR stratification conditions, and then, the potential of in-cylinder EGR stratification was studied by using the FSE model. The effect of in-cylinder EGR stratification was verified under various injection timing, engine speed, and road conditions with optimized engine geometries. The results shows simultaneous NOx and soot reductions under the stratified EGR condition.     

Combustion and emission characteristics of BD20 reformed by ultrasonic energy for different injection delay and EGR rate in a diesel engine

The purpose of this study is to understand the operational characteristics of a diesel engine that uses BD20 reformed by ultrasonic energy irradiation. In particular we study the effects of tuning injection delay and EGR rate. BD containing about 10% oxygen has attracted attention due to soaring crude oil prices and environmental pollution. This oxygen decreases soot by promoting combustion, but it also increases NOx. To solve this problem, injection timing may be delayed or an EGR system may be applied. These adjustments normally lower engine power and increase exhaust emission but, in using fuel reformed by ultrasonic energy irradiation (which is changed physically and chemically to promote combustion), we may hope to circumvent this problem. To control the duration of the ultrasonic energy irradiation, the capacity of the chamber in an ultrasonic energy fuel supply system was tested at 550cc and 1100cc capacities. As for the results of the experiment, we could identify the optimum EGR rate by investigating the engine performance and the characteristics of exhaust emissions according to the injection timing and the EGR rate while ultrasonically irradiated BD20 was fed to a commercial diesel engine. With UBD20 (at an injection timing of BTDC 16°), the optimum EGR rate, giving satisfactory engine performance and exhaust emissions characteristics, was in the range of 15∼20%.     

外部热EGR对基于优化动力技术的汽油HCCI燃烧的影响

考察了外部热EGR对基于优化动力技术的汽油HCCI发动机燃烧的影响。试验结果表明:外部热EGR可以推迟HCCI燃烧的着火时刻,减缓放热速率,但对于高辛烷值燃料的HCCI燃烧,它对更高EGR率的兼容能力不强,需要提高进气温度来提高燃烧的稳定性;随着EGR率的增加,燃烧持续期延长,缸内温度和压力峰值均减小,指示热效率也随着减小;NOx排放随着EGR率的增加在经过一个"拐点"后始终维持在一个较低的水平,而CO和HC的排放随着EGR率的增加显著增加,燃烧恶化。     

Characteristics of gasoline in-cylinder direct injection engine

Combustion characteristics of a gasoline direct-injection (DI) engine were studied with fuel injection timing varied. This study showed that emissions at part load are reduced by optimizing in-cylinder air motion and injection timing. Antiknock quality and volumetric efficiency are improved at high loads. With our DI system fuel does not stick on the intake port wall during engine warmup and transient mode, and thus even a cold engine can be controlled with a quick response and a high resolution, which, as a result, can reduce emissions. Also, lean limit is significantly improved by optimizing the injection timing.     

Exhaust emissions and its control methods in compression ignition engines: A review

Extensive usage of automobiles has certain disadvantages and one of them is its negative effect on environment. Carbon dioxide (CO₂), carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NO_x), sulphur dioxide (SO₂) and particulate matter (PM) come out as harmful products during incomplete combustion from internal combustion (IC) engines. As these substances affect human health, regulatory bodies impose increasingly stringent restrictions on the level of emissions coming out from IC engines. This trend suggests the urgent need for the investigation of all aspects relevant to emissions. It is required to modify existing engine technologies and to develop a better after-treatment system to achieve the upcoming emission norms. Diesel engines are generally preferred over gasoline engines due to their undisputed benefit of fuel economy and higher torque output. However, diesel engines produce higher emissions, particularly NO_x and PM. Aftertreatment systems are costly and occupy more space, hence, in-cylinder solutions are preferred in reducing emissions. Exhaust gas recirculation (EGR) technology has been utilized previously to reduce NO_x. Though it is quite successful for small engines, problem persists with large bore engines and with high rate of EGR. EGR helps in reducing NO_x, but increases particulate emissions and fuel consumption. Many in-cylinder solutions such as lower compression ratios, modified injection characteristics, improved air intake system etc. are required along with EGR to accomplish the future emission norms. Modern combustion techniques such as low temperature combustion (LTC), homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI) etc. would be helpful for reducing the exhaust emissions and improving the engine performance. However, controlling of autoignition timing and achieving wider operating range are the major challenges with these techniques. A comprehensive review of diesel engine performance and emission characteristics is given in this paper.     

Numerical study of a light-duty diesel engine with a dual-loop EGR system under frequent engine operating conditions using the doe method

Exhaust gas recirculation (EGR) is an emission control technology that allows for a significant reduction in NOx emissions from light- and heavy-duty diesel engines. The primary effects of EGR are a lower flame temperature and a lower oxygen concentration of the working fluid in the combustion chamber. A high pressure loop (HPL) EGR is characterized by a fast response, especially at lower speeds, but is only applicable if the turbine upstream pressure is sufficiently higher than the boost pressure. On the contrary, for the low pressure loop (LPL) EGR, a positive differential pressure between the turbine outlet and the compressor inlet is generally available. However, a LPL EGR is characterized by a slow response, especially at low and moderate speeds. In this study, of the future types of EGR systems, the dual-loop EGR system (which has the combined features of the high-pressure loop EGR and the low-pressure loop EGR) was developed and was optimized under five selected operating conditions using a commercial engine simulation program (GT-POWER) and the DOE method. Finally, significant improvements in the engine exhaust emissions and performance were obtained by controlling several major variables.     

EGR对柴油-天然气双燃料发动机稀燃的影响

在一台由柴油机加装天然气供给系统改装而成的双燃料发动机上进行试验,分别研究了EGR率和过量空气系数(a)随喷油提前角变化对双燃料发动机的影响。结果表明:当EGR率为0时,a过大导致热效率降低。增大喷油提前角使着火提前,燃烧得以改善,最大压力升高率和最高燃烧压力提高,热值折合燃料消耗率降低。喷油提前角一定时,最大压力升高率、最高燃烧压力随EGR率的增大先升高后降低,热值折合燃料消耗率先降低后升高,EGR率为20%时热值折合燃料消耗率达到最低值。采用EGR技术能有效降低NOx排放,但HC,CO,CH4和炭烟排放随着EGR率的增大而增大;增大喷油提前角使缸内柴油预混燃烧比例增加,HC,CO,CH4和炭烟排放降低。因此,采用EGR时应适当增加喷油提前角。     

EGR柴油机瞬态性能优化研究

以降低瞬态过程烟度和NO_x排放为目标,在一台高压共轨电控重型柴油机上进行了EGR对柴油机恒转速增扭矩5s典型瞬态过程燃烧和排放性能影响的优化研究。结果表明:瞬态过程中固定EGR阀开度造成EGR率"超调"、烟度剧增;与"全程轨压"策略相比,"分段轨压"有利于改善小负荷工况的燃烧热氛围,提高瞬态起始负荷并耦合"分段轨压"可以有效降低瞬态过程烟度峰值;EGR阀的开闭对瞬态性能影响最大,瞬态过程1.5s关阀、4s开阀的策略可以实现较好的烟度和NO_x排放折中,消光烟度峰值为9.2%,NO_x峰值稍有增加但增幅不大。     

Operating strategy for gasoline/diesel dual-fuel premixed compression ignition in a light-duty diesel engine

Environmental problems have become a major issue for diesel engine development. Although emission aftertreatment systems such as DPFs (diesel particulate filters), LNTs (lean NOx traps) and SCR (selective catalytic reduction) have been used in diesel vehicles, the manufacturing cost increase caused by this equipment can be hard to be control. Thus, it is better for engine emissions to be reduced by improving the combustion system. A dual-fuel combustion concept is a recommended method to improve a combustion system and effectively reduce emissions. Low reactivity fuel including gasoline and natural gas, which was supplied to the intake port by the FPI (port fuel injector), improved the premixed air-fuel mixture conditions before ignition. Additionally, a small amount of high reactivity fuel, in this case diesel, was injected into the cylinder directly as an ignition source. This dual-fuel combustion promises lower levels of NOx (nitrogen oxide) and PM (particulate matter) emissions due to the elimination of local rich regions in the cylinder. However, it is challenging to control the dual-fuel combustion because the combustion stability and efficiency deteriorate due to the lack of ignition source and reactivity. Thus, it is important to establish an appropriate dual-fuel operating strategy to achieve stable, high efficiency and low emission operation. As a result of this research, a detailed operating method of dual-fuel PCI (premixed compression ignition) was introduced in detail at a low speed and low load condition by using a single cylinder diesel engine. Engine operating parameters including the gasoline ratio, a diesel injection strategy consisting of multiple injectors and timing, the EGR (exhaust gas recirculation) rate and the intake pressure were controlled to satisfy the low ISNOx (indicated specific NOx) and PM emissions levels (0.21 g/kWh and 0.1 FSN, 0.040 g/kWh, respectively) as per the EURO-6 regulation without any after-treatment systems. The results emphasized that a well-constructed dual-fuel PCI operating strategy showed low NOx and PM emissions and high GIE (gross indicated fuel conversion efficiency) with excellent combustion stability.     

Enhancement of NOx-PM trade-off in a diesel engine adopting bio-ethanol and EGR

For realizing a premixed charge compression ignition (PCCI) engine, the effects of bio-ethanol blend oil and exhaust gas recirculation (EGR) on PM-NOx trade-off have been investigated in a single cylinder direct injection diesel engine with the compression ratio of 17.8. In the present experiment, the ethanol blend ratio and the EGR ratio were varied focusing on ignition delay, premixed combustion, diffusive combustion, smoke, NOx and the thermal efficiency. Very low levels of 1.5 [g/kWh] NOx and 0.02 [g/kWh] PM, which is close to the 2009 emission standards imposed on heavy duty diesel engines in Japan, were achieved without deterioration of the thermal efficiency in the PCCI engine operated with the 50% ethanol blend fuel and the EGR ratio of 0.2. It is found that this improvement can be achieved by formation of the premixed charge condition resulting from a longer ignition delay. A marked increase in ignition delay is due to blending ethanol with low cetane number and large latent heat, and due to lowering in-cylinder gas temperature on compression stroke based on the EGR. It is noticed that smoke can be reduced even by increasing the EGR ratio under a highly premixed condition.     

Combustion stability analysis during engine stop and restart in a hybrid powertrain

A cycle-resolved analysis system was designed with the specified measurement instruments to investigate the characteristics of combustion stability in a mild gasoline hybrid powertrain. A Fast Response Flame Ionization Detector (FFID), cylinder pressure transducer and engine torque transducer were used to observe both the engine-out THC emissions and engine performance during a brief moment of engine restart. This research aimed to improve combustion stability and was performed by varying the battery State Of Charge (SOC), injection duration and ignition timing. The results indicate that engine combustion tends to be more stable with longer fuel injection durations and advanced ignition timing, while the effect of the battery SOC is negligible. Also, peculiar differences in the catalyst conversion efficiency at the front and rear of the catalyst during engine restart and deceleration were revealed, with the degree of HC oxidation being the suspected cause. This study not only analyzed the engine control and engine-out total hydrocarbon (THC) emission characteristics, but also implemented control strategies that allowed for combustion stability during engine stop and restart operation.     

负荷控制方式对甲醇发动机性能影响的试验研究

在1台2L柴油机改装的点火式甲醇发动机上分别采用节气门、节气门联合EGR以及单纯EGR的方式来控制发动机负荷,试验负荷选择了全负荷的50%和75%,过量空气系数保持在1附近,调整点火角,进行动力性和排放性试验。研究发现:两种负荷下都是采用节气门联合EGR控制负荷时发动机的动力性和经济性最好;两种负荷下的HC排放随控制方式的不同而不同,但均为节气门控制负荷时HC排放最低;两种负荷下的CO排放随控制方式的不同而不同,但都是节气门控制负荷时CO排放最高;两种负荷下的NOx排放规律相似,均为节气门开度越大,NOx排放越低。     

EGR对高压共轨柴油机小负荷工况燃烧过程及排放性能的影响

以某轻型车用高压共轨柴油机为样机,研究了在小负荷工况条件下,EGR率对柴油机排放、燃烧过程及燃油消耗的影响。试验结果表明:EGR减小了缸内最高燃烧压力及压力峰值,使压力升高率略有增加,降低了瞬时放热率与峰值,延长了燃烧持续期,降低了缸内温度峰值及平均温度。在小负荷工况,EGR可以同时有效改善NOx,HC及CO排放,当EGR阀全开,EGR率为42%时,NOx排放降低了38.7%,HC降低了39.6%,CO排放降低了21.3%;PM排放先随着EGR率增加而减小,EGR率超过某一值后,PM排放增加,整个PM排放曲线呈现"鱼钩"状变化趋势。EGR对小负荷工况燃油耗性能影响不大。     

内外EGR和喷油压力对柴油机低温燃烧的影响

在1台装有电液可变气门的单缸柴油机上,通过改变内外EGR策略和喷油压力,对柴油机小负荷工况下低温燃烧的燃烧特性和排放特性进行了试验研究。内部EGR通过排气门两次开启实现,发动机转速和喷油量分别固定为1 500r/min和20mg/cycle。研究结果表明,通过高EGR率控制可以实现超低NOx排放,其中采用高喷油压力可以降低内部EGR的炭烟排放,而采用低喷油压力可以降低外部中冷EGR的HC和CO排放。在内外EGR耦合控制策略中,提高内部EGR比例可以降低HC和CO排放,但改善效果逐渐减弱,同时为了抑制炭烟排放,需要结合更高喷油压力,而提高外部中冷EGR比例可以获得较高热效率。     

Evaluation and visualization of stratified ultra-lean combustion characteristics in a spray-guided type gasoline direct-injection engine

To comply with reinforced emission regulations for harmful exhaust gases, including carbon dioxide (CO₂) emitted as a greenhouse gas, improved technologies for reducing CO₂ and fuel consumption are being developed. Stable lean combustion, which has the advantage of improved fuel economy and reduced emission levels, can be achieved using a sprayguided-type direct-injection (DI) combustion system. The system comprises a centrally mounted injector and closely positioned spark plugs, which ensure the combustion reliability of a stratified mixture under ultra-lean conditions. The aim of this study is to investigate the combustion and emission characteristics of a lean-burn gasoline DI engine. At an excess air ratio of 4.0, approximately 23% improvement in fuel economy was achieved through optimal event timing, which was delayed for injection and advanced for ignition, compared to that under stoichiometric conditions, while NO_x and HC emissions increased. The combustion characteristics of a stratified mixture in a spray-guided-type DI system were similar to those in DI diesel engines, resulting in smoke generation and difficulty in three-way catalystutilization. Although a different operating strategy might decrease fuel consumption, it will not be helpful in reducing NO_x and smoke emissions; therefore, alternatives should be pursued to achieve compliance with emission regulations.     

Effects of the throttle opening ratio and the injection timing of CNG on the combustion characteristics of a DI engine

We investigated the effects of the fuel injection timing — both for early and late injection — in conjunction with the throttle opening ratio on the fuel-air mixing characteristics, engine power, combustion stability and emission characteristics of a DI CNG spark engine and control system that had been modified and designed according to the author’s original idea. We verified that the combustion characteristics were affected by the fuel injection timing and that the engine conditions were affected by the throttle opening ratios and the rpm. The combustion characteristics were greatly improved for a complete open throttle ratio with an early injection timing and for a partial throttle ratio with a late injection timing. The combustion duration was governed by the duration of flame propagation in late injection timing scenarios and by the duration of early flame development in cases of early injection timing. As the result, the combustion duration is shortened, the lean limit is improved, the air-fuel mixing conditions are controlled, and the emissions are reduced through control of the fuel injection timing and vary according to ratio of the throttle opening.     

Model based burnt gas fraction controller design of diesel engine with VGT/Dual loop EGR system

-Recently, regulation of NOx and PM emission in diesel engines has become stricter and the EGR system has been expanded into a dual loop EGR system to increase EGR rate as well as to utilize exhaust gas strategically. In terms of engine combustion characteristics, burnt gas fraction is becoming an important factor of solving the NOx and PM emission reduction problem more efficiently but conventional controller focused only pressure and air flow rate targets. Unlike the previous studies, this paper describes a model based burnt gas fraction control structure for a diesel engine with a dual loop EGR and a turbocharger. Feedforward control inputs based on burnt gas fraction states aids in the precise control of diesel engines, especially in transient states by considering coupled behavior within the system. For the controller validation, a control oriented reduced order model of a diesel engine air management system is established to simplify the control input computation and its stability is proved by analysing the internal dynamics stability. Then, a sliding mode controller is designed and controller robustness at certain operating points is validated using an HiLS bench.     

Experimental investigation of B20 combustion and emissions under various intake conditions for low-temperature combustion

Recently, biodiesel has emerged as an alternative fuel for achieving low-temperature combustion (LTC). Several articles in the literature have showed that oxygenated biofuels, including biodiesel, can improve combustion stability under high exhaust gas recirculation (EGR) operation, which is considered to be necessary for the removal of nitric oxides (NOx). The objective of this study was to investigate the performance and emissions of 20% biodiesel blended diesel fuel (B20) at various intake pressures and oxygen concentration levels to characterize the fuel for LTC application. The experimental investigation of B20 was carried out using a single-cylinder engine (SCE) at 1400 rpm and 50% load condition. A set of critical flow orifices with synthetic EGR was employed to simulate various intake pressures and EGR levels. The behavior of the B20 was first characterized under various intake conditions. The results showed that with high oxygen intake, B20 exhibited combustion and emission levels that were very similar to conventional diesel. However, B20 reduced combustion deterioration while exhibiting lower carbon monoxide (CO) and hydrocarbon (HC) emissions than diesel under low oxygen intake conditions.