Diesel Combustion Process Research Articles

Numerical simulation of diesel combustion based on n-heptane and toluene

Considering the self-ignition characteristic and C/H ratio, n-heptane and toluene (6:4 by mass) are chosen to constitute diesel surrogate fuel, and a reduced oxidation mechanism was developed. This mechanism was firstly validated by the combustion of diesel fuel in different oxygen concentrations within a constant volume vessel by high-speed photography. The simulated flame temperature distribution reproduces the diesel combustion process quite well. For further validation, combustion in real diesel engine was also investigated numerically and experimentally using a light duty diesel and a marine diesel. The calculated pressure curves in different operation conditions fit the measured data reasonably well. The oxidation mechanism could reproduce the main characteristics including combustion phase and NOx emission of diesel combustion in different cases.

Unsupervised learning and nonlinear identification for in-cylinder pressure prediction of diesel combustion rate shaping process

Combustion Rate Shaping (CRS) offers the potential to control in-cylinder fuel concentration gradient and distribution with new fuel injection strategies, consisting of a higher number of injections and smaller individual injection quantities. Developing a physics-based model for such strategies involves significant development efforts and is also associated with high computational cost. This paper proposes a black-box framework for CRS process control based on artificial neural network and principal components analysis. To identify the nonlinear system behavior of diesel combustion, a multi-input/multi-output empirical model has been developed. The cylinder pressure trace is transformed into principal components coefficients space, and the neural network is used to predict the coefficients from operation parameters of diesel combustion. The in-cylinder pressure trace is then reconstructed by the predicted coefficients and pre-extracted principal components. The model has been evaluated with specific combustion features of CRS diesel engine experiments. The results show that the model successfully captured the combustion characteristics of CRS based diesel combustion processes with sufficient generalization ability.

Research of performance and emission indicators of the compression-ignition engine powered by hydrogen - Diesel mixtures

The purpose of this study is to use the hydrogen – diesel mixture in Audi/VW 1.9 TDI turbocharged CI engine equipped with dynamometer and examine the performance and emission indicators by comparing it with sole diesel mode. The recent diesel emission scandals because of manufacturers cheating the laboratory tests, have initiated the discussions about the sustainable and environmentally friendly diesel engines. The CI engine without major engine modifications was set to operate at two speeds of 1900 rpm and 2500 rpm. At each of speed, the experiment was conducted at three BMEP: 0.4 MPa, 0.6 MPa, and 0.8 MPa. The test engine was operated using diesel fuel with amounts of 10 l/min, 20 l/min, and 30 l/min of hydrogen gas, supplied with air into intake manifold before the turbocharger. Relatively low hydrogen fraction (max. 15.74%) has effect on diesel combustion process and performance indicators at the all range of BMEP. The in-cylinder peak pressure at both speeds of 1900 rpm and 2500 rpm was lower than that with pure diesel fuel, as the small amount of hydrogen shortens the CI engine ignition delay period and decreases the rate of pressure rise. The decrease of BTE noticed, and increase of BSFC was registered with low hydrogen fraction (hydrogen amounts of 10 l/min, 20 l/min). However, with increase of hydrogen amount to 30 l/min, the BTE increased and BSFC decreased to the level, which was lower than that at the pure diesel test. The supply of hydrogen positively effects on engine emissions: the smokiness, NOx, CO2, CO decreased, the only hydrocarbon increased. The effect of hydrogen fraction on the combustion and emission characteristics of the diesel - hydrogen mixture was validated by AVL (Anstalt für Verbrennungskraftmaschinen List) BOOST and analysed with presentations of the main limitations and perspectives.

Numerical Investigation of Combustion and Emission With Different Diesel Surrogate Fuel by Hybrid Breakup Model

Injection flow dynamics plays a significant role in fuel spray; this process controls the fuel–air mixing, which in turn is critical for the combustion and emissions process in diesel engine. In the current study, an integrated spray, combustion, and emission numerical model is developed for diesel engine computations based on the general transport equation analysis (GTEA) code. The model is first applied to predict the effect of turbulence inside the nozzle, which is considered by the submodel of hybrid breakup model on diesel spray process. The results indicate that turbulence term enhances the rate of breakup, resulting in more new droplets and smaller droplet sizes, leading to high evaporation rate with more evaporated mass. The model is also applied to simulate combustion and soot formation process of diesel. The effects of ambient density, ambient temperature, oxygen concentration and reaction mechanism on ignition delay, flame lift-off length, and soot formation are analyzed and discussed. The results show that although higher ambient density and temperature reduce the ignition delay and cause the flame stabilization location to move upstream, this is not helpful for fuel–air mixing because it increases the soot level in the fuel jet. While higher oxygen concentration has negative effects on soot formation. In addition, the model is employed to simulate the combustion and emission characteristics of a low-temperature combustion engine. The overall agreement between the measurements and predictions of in-cylinder pressure, heat release, and emission characteristics are satisfactory.

Thermogravimetric study of the combustion characteristics of biodiesel and petroleum diesel

The thermal behavior of biodiesel and a comparison with a petroleum diesel combustion process was investigated via thermogravimetric analysis. The investigation was carried out under atmospheric conditions of pure air flow at four different heating rates, reaching a temperature of 700 °C. Beyond the initiation (a fraction of mass loss) stage of the thermograph, the diesel exhibited only one mass loss event, whereas the biodiesel was characterized with two mass loss events. The ignition and burnout temperatures are essential properties of fuel combustion used in their industrial application, and they were evaluated using numerous methods at every heating value. The kinetic parameters were also calculated using the Kissinger method. The values obtained for the main mass loss event I, devolatilization, were 98.8 and 63.4 kJ mol−1, respectively, for the biodiesel and diesel. Additionally, the thermodynamic parameters were calculated including the enthalpy, Gibbs free energy and entropy and found to be 94.3 kJ mol−1, 158 kJ mol−1 and − 0.116 kJ mol−1 for the biodiesel, compared to 59.2 kJ mol−1, 150.5 kJ mol−1 and − 0.117 kJ mol−1 for the diesel, respectively. Results indicate better reactivity in favor of the petroleum diesel. Hence, utilizing biodiesel at 100% for utility burners and internal combustion engine may require some additives to compensate the change and the measured lower heating value (~ ≤ 5%). Therefore, blending has been the simplest practical approach.

Systematic Design of Multivariable Fuel Injection Controllers for Advanced Diesel Combustion

With multiple fuel injections per combustion cycle, the advanced diesel combustion process depends on all injection pulses in a coupled way. This makes the control of the multipulse fuel injection profile challenging, and the currently employed decoupled design methods might fail to guarantee closed-loop stability. Without explicit consideration of disturbances, it is also difficult for current design methods to guarantee the robustness of a fuel injection controller. In this paper, we present a general framework that describes the cycle-to-cycle fuel injection control problem. A control-oriented model is introduced and locally validated with experimental data. It considers the disturbances and captures the coupled relation between the multipulse fuel injection profile and the combustion process. Based on the general framework and the control-oriented combustion model, we propose a systematic design approach to synthesize a multivariable fuel injection controller. With guaranteed robust stability and fast settling time (0.5 seconds/5 combustion cycles in experiments), the controller’s reference tracking performance and disturbance rejection capability are demonstrated experimentally on a single-cylinder engine test bench.

Combustion process decoupling of a diesel/natural gas dual-fuel engine at low loads

The combustion process of diesel/natural gas dual-fuel engine is complicated. In order to decouple the combustion process of natural gas (NG) and diesel, a wide range of the NG from zero to 75%, by increasing the NG flow rate at a constant air and diesel consumption rate were studied. A detailed analysis based on heat release rate data has been carried out to better understand the effect and underlying mechanism of the two fuel combustion processes. A method of calculating the ratio of heat release from NG combustion to the total heat release through comparing the heat release rate data between dual-fuel mode at different NG quantities and original diesel mode was proposed. The tested engine is a 6-cylinder turbocharged intercooler dual-fuel engine. Several combustion parameters, including in-cylinder pressure, in-cylinder temperature and heat release rate, were analyzed under 1335 rpm, 10% load (A10) condition and 1335 rpm, 25% load (A25) condition. The results show that the heat release rate curves have only one peak firstly, then transform into two peaks, and change into a quasi-single peak at last with the increase of NG quantities under A10 condition when Tinj is 7°CA BTDC. The maximum ratio of heat release from combustion by NG around diesel spray to the total heat release is 25.4% and the premixed combustion of diesel occupies the main combustion process, the maximum ratio of heat release from combustion by flame propagation of NG to the total heat release is 75.4% (PES is 73%) and the combustion of NG is the main part of the combustion process. A similar discussion under A25 condition when Tinj is 7°CA BTDC and about advancing and retarding Tinj under A10 condition was conducted.

Single-cylinder engine evaluation of a multi-component diesel surrogate fuel at a part-load operating condition with conventional combustion

Simple, yet fully-representative surrogate fuels are needed to model market Diesel fuels. The surrogates must closely mimic market Diesel fuel properties and match the engine combustion and emissions behavior. To this end, the combustion and emissions performance of a market Diesel fuel and a four-component surrogate fuel were investigated using a single-cylinder, light-duty Diesel engine with contemporary combustion and fuel injection technology. The surrogate fuel, which was developed in previous work, was composed of normal-hexadecane/2,2,4,4,6,8,8-heptamethylnonane/decahydronaphthalene/1-methylnaphthalene with a volume fraction formulation of 0.37/0.33/0.18/0.12. Fuel test results showed the physical, chemical and combustion properties of the market Diesel fuel were closely matched by the surrogate. The fuels were evaluated by engine tests conducted at 1500 r/min and 9 bar IMEP. At this operating condition, the Diesel combustion process demonstrated low-temperature heat release, premixed and diffusion combustion regions. Test results from EGR and combustion phasing sweeps showed the engine combustion behavior, exhaust CO, HC, NOx, smoke and particle size distributions from the market Diesel fuel were very closely matched by the surrogate fuel. It can be concluded that under the engine conditions evaluated by this work, the four-component surrogate fuel accurately represents the market Diesel fuel. Thus, for conventional Diesel combustion conditions, the surrogate should prove useful for future applications such as kinetic mechanism development, fuel spray and combustion simulation, and further experimental investigations.

Study on Relation between Combustion Process and Unburned Hydrocarbons Production in Diesel Combustion

Study on Relation between Combustion Process and Unburned Hydrocarbons Production in Diesel Combustion

Real-time capable simulation of diesel combustion processes for HiL applications

The complexity of the development processes for advanced diesel engines has significantly increased during the last decades. A further increase is to be expected, due to more restrictive emission legislations and new certification cycles. This trend leads to a higher time exposure at engine test benches, thus resulting in higher costs. To counter this problem, virtual engine development strategies are being increasingly used. To calibrate the complete powertrain and various driving situations, model in the loop and hardware in the loop concepts have become more important. The main effort in this context is the development of very accurate but also real-time capable engine models. Besides the correct modeling of ambient condition and driver behavior, the simulation of the combustion process is a major objective. The main challenge of modeling a diesel combustion process is the description of mixture formation, self-ignition and combustion as precisely as possible. For this purpose, this article introduces a novel combustion simulation approach that is capable of predicting various combustion properties of a diesel process. This includes the calculation of crank angle resolved combustion traces, such as heat release and other thermodynamic in-cylinder states. Furthermore, various combustion characteristics, such as combustion phasing, maximum gradients and engine-out temperature, are available as simulation output. All calculations are based on a physical zero-dimensional heat release model. The resulting reduction of the calibration effort and the improved model robustness are the major benefits in comparison to conventional data-driven combustion models. The calibration parameters directly refer to geometric and thermodynamic properties of a given engine configuration. Main input variables to the model are the fuel injection profile and air path–related states such as exhaust gas recirculation rate and boost pressure. Thus, multiple injection event strategies or novel air path control structures for future engine control concepts can be analyzed.

Effects of different aromatics blended with diesel on combustion and emission characteristics with a common rail diesel engine

Aromatic hydrocarbons are thought to be the important components of diesel surrogate fuel. The studies on the effects of different aromatic hydrocarbons on diesel combustion process are of great significance. In this paper, experimental study was carried out on a modified single cylinder diesel engine to analyze the influences of different aromatics blended with diesel on the combustion and emission characteristics. Four typical aromatics (toluene, n-butylbenzene, tetralin and 1-methylnaphthalene) were selected and blended with commercial diesel fuel in 30% volume fraction to form the test fuels, respectively. Studies showed that the blending of aromatics resulted in the higher density and lower viscosity compared with traditional diesel fuel. Toluene lowered the distillation temperature of the mixed fuel to a large extent. The increases in both the ignition delay and the peak values of heat release rate were found in the experiments. The combustion duration was shortened especially for the multi-ring aromatics. It also increased maximum pressure rise rate remarkably at medium and high loads. As for the pollutant emissions, the higher CO emissions were detected at low loads for aromatics/diesel blends. The CO emissions of the multi-ring aromatics were higher than those of the single-ring aromatics and commercial diesel. HC emissions of the multi-ring aromatics were higher than those of diesel, while the single-ring aromatics had similar HC emissions to those of diesel. Blending aromatics leaded to the higher NOx emissions at medium-high loads. Smoke emissions were improved due to the longer ignition delay. The peak value of particle number/size distribution curve was shifted to the small-size sides after blending aromatics, in which the single-ring aromatics showed higher particle emissions than multi-ring aromatics.

Extended modeling of decelerating turbulent jets for diesel spray's penetration after end-of-injection

In order to meet the growing demand for reduction of pollutant emissions and improvement in thermal efficiency, advanced combustion modes, such as low-temperature combustion (LTC), premixed charge compression ignition (PCCI), have been adopted in modern diesel engines. Compared to conventional diesel combustion, the ignition delay becomes longer in advanced combustion modes. The longer ignition delay usually results in the fuel injection ending earlier than ignition. Therefore, the spray propagation after end-of-injection (EOI) plays a significant role in diesel combustion process, and it is needed to estimate the spray evolution and mixture formation after EOI. For this purpose, a simple and analytical diesel spray model including the spray evolution after the EOI is developed in this study. To develop the model, the theoretical analysis on the decelerating process of the turbulent jet tip is performed based on the integral momentum flux and mass flow rate of the injected fluid over the cross-sectional area at the jet tip. It is observed that the decrease of mass flow rate of the injected fluid over the tip cross-sectional area causes reduction of the momentum flux over the tip cross-sectional area and the turbulent jet tip decelerating. Then the mass flow rate of injected fluid over the tip cross-sectional area is formulated, furthermore the analytical equation of the turbulent jet tip penetration during decelerating state is derived, and the correctness of the developed analytical equation has been proved theoretically. Finally, the calculation is extended to diesel spray penetration, and the calculated results are validated against the one-dimensional discrete model and the experimental data from Engine Combustion Network (ECN) respectively.

Comparision on dynamic behavior of diesel spray and rapeseed oil spray in diesel engine

Fuel-air mixing is important process in diesel combustion. It significantly affects the combustion and emission of diesel engine. Biomass fuel has high viscosity and high distillation temperature and may negatively affect the fuel-air mixing process. Thus, study on the spray development and atomization of this type of fuel is important. This study investigates the atomization characteristics and droplet dynamic behaviors of diesel engine spray fuelled by rapeseed oil (RO) and comparison to diesel fuel (GO). Optical observation of RO spray was carried out using shadowgraph photography technique. Single nano-spark photography technique was used to study the characteristics of the spray while dual nano-spark shadowgraph technique was used to study the spray droplet behavior. Using in-house image processing algorithm, the images were processed and the boundary condition of each spray was also studied. The results show that RO has very poor atomization due to the high viscosity nature of the fuel when compared to GO. This is in agreement with the results from spray droplet dynamic behavior studies that shows due to the high viscosity, the RO spray droplets are large in size and travel downward, with very little influence of entrainment effect due to its large kinematic energy.

Microwave Susceptible Catalytic Diesel Particulate Filter

The diesel internal combustion engine is one of the most environmentally-friendly vehicle devices, because it emits less carbon dioxide and is more fuel efficient than the universal gasoline stoichiometric engine. However, considerable challenges still exist regarding the emission control of particulate matter (PM), commonly known as soot, emitted by the diesel combustion process. These ultrafine particles, which have aerodynamic diameters of less than 2.5 ?m (PM2.5), are problematic as they can cause serious respiratory diseases, including lung cancer and chronic obstructive pulmonary disease. Various filters are commonly used for soot abatement in diesel exhaust, while catalytic oxidation is preferable to intensify burning of soot trapped in filters. The diesel particulate filters (DPFs) are the most important technologies to maintain soot emissions under EU regulations, consisting in alternately plugged parallel square channels, so that the exhaust gases are forced to flow through the porous inner walls: in this way the particles are collected on the surface and in the porosity of the channel walls, progressively blocking the pores. Since the pressure loss increases by the formation of a thick soot cake as the PM is accumulated, the DPF needs to be periodically regenerated by burning off the accumulated soot. The results of our previous deposition and on-line regeneration tests on uncatalysed and Copper-Ferrite catalysed DPF, showed that the simultaneous use of a catalyst properly formulated and microwaves during the regeneration step at lower gas flow rate, allows to reduce the energy supplied and the regeneration time than that required for the uncatalysed filter. Starting by these very promising results, the objectives of this work are to increase the active species load simultaneously modifying the porosimetric characteristics of the support, in order to simultaneously further reduce the PM oxidation temperature and keep low the pressure drop.

Numerical investigation of soot formation and oxidation processes under large two-stroke marine diesel engine-like conditions using integrated CFD-chemical kinetics

In this reported work, multi-dimensional computational fluid dynamics studies of diesel combustion and soot formation processes in a constant volume combustion chamber and a marine diesel engine are carried out. The key interest here is firstly to validate the coupling of a newly developed skeletal n-heptane mechanism and a revised multi-step soot model using laser extinction measurements of diesel soot obtained at different ambient pressure levels in an optical accessible, constant volume chamber experiment. It is revealed that ignition delay times and liftoff lengths generated using the new skeletal model are close to those produced by the larger and more comprehensive chemical mechanisms, apart from those at the low pressure condition. The current study also demonstrates that the variation of averaged soot volume fraction with respect to the change of combustion chamber pressure captured using the revised soot model agrees reasonably well with the measurements in terms of peak values. The numerical model is subsequently applied to investigate the flame development, soot/nitrogen monoxide formation and heat transfer in a two-stroke, low-speed uniflow-scavenged marine diesel engine operating at full load condition, where optical measurements are not available. Comparisons to the experimental data show that the simulated pressure rise starts 1.0 crank angle degree in advance and the calculated peak pressure is 1.7% lower. The associated flame liftoff length is negligible, yielding higher local equivalence ratio and soot volume fraction values as compared to those under similar test condition in the constant volume chamber. With the use of the revised model, the total heat transfer to the walls calculated when soot radiative heat loss is taken into account is approximately 30% higher compared to that when only convective heat loss is considered. The averaged nitrogen monoxide concentration is 7.7% lower when both convective and soot radiative heat losses are accounted for but the net soot mass production is less sensitive to soot radiation. A sensitivity study reveals that neither increasing nor decreasing the soot absorption coefficient by 30% from the baseline setup is influential to nitrogen monoxide formation, soot mass production and heat transfer. The findings here aid to gain insights and provide a better understanding of the combustion and soot processes in large, uniflow-scavenged marine engines. The numerical model developed in this work can also be applied to explore different phenomena in this combustion system.

On-line thermodynamic diagnosis of diesel combustion process with paraffinic fuels in a vehicle tested under NEDC

The increasing interest for using alternative fuels, more environmentally friendly compared to fossil fuels, has motivated this research work. The knowledge of the combustion process with these fuels provides an important tool for increasing performance and for reducing pollutant emissions. This knowledge allows a better calibration of engine parameters configured in the Electronic Control Unit. For this reason, this paper presents the evolution of the main parameters of the combustion process of a light-duty vehicle equipped with a Euro 4 diesel engine, operating with gas to liquid fuel, a hydrotreated vegetable oil fuel, and a commercial diesel fuel (with 5.8% of biodiesel) as reference. Tests were carried out on a chassis dynamometer under controlled ambient conditions following the New European Driving Cycle. One of the engine cylinders was instrumented with a Kistler Kibox device combined with an opened electronic control unit and a system for online thermodynamic combustion diagnosis. Thermodynamic diagnosis parameters have been compared, at different time windows, along the New European Driving Cycle. Results also show that the effect of cetane number of fuels on ignition delay can be appreciated at the beginning of NEDC (1st U) and, more strongly, in the rest of the cycle. It is remarkable that paraffinic fuels show better indicated efficiency because of the more centered combustion (around the Top Dead Center). Diesel fuel shows higher maximum apparent heat release which is indicative of faster combustion process and higher ignition delay.

M503 素反応機構および修正したWAVE-MTABモデルを用いたディーゼル噴霧および燃焼過程のLES解析(GS7 ディーゼル噴霧・燃焼(1),修士研究発表セッション)

M503 素反応機構および修正したWAVE-MTABモデルを用いたディーゼル噴霧および燃焼過程のLES解析(GS7 ディーゼル噴霧・燃焼(1),修士研究発表セッション)

Alternative method for bulk modulus estimation of Diesel fuels

The knowledge of Diesel fuel properties has great relevance for the analysis and comprehension of phenomena related to fuel injection, fuel–air mixture formation and diesel combustion processes. This work proposes an alternative method for estimating the bulk modulus of diesel fuels by means of an experimental installation commonly used for determining fuel injection rates from common rail injection systems. Three fuels were tested in the mentioned installation: commercial Diesel fuel (blended with 5.8% of biodiesel), hydro-treated vegetal oil (HVO) and gas to liquid (GTL) fuel from natural gas by means of low temperature Fischer Tropsch process. Results were obtained by testing two different injectors (solenoid operated and piezoelectric injectors) under different injection pressures and energizing times. Fuel temperature at inlet of the high pressure injection pump was controlled, keeping constant the pressure inside the fuel injection indicator. From the experimental work, data analysis and post-processing, bulk modulus of fuels tested has been estimated and compared to results obtained by diverse authors with different experimental installations and methods. Results obtained in this work show small differences compared to published data. Additionally, the initial time lag between the signal of the electric pulse when the injector is energized and the beginning of the injection rate profile depends only on the type of injector without influence of type of fuel and operating conditions. However, the rear time lag between both mentioned profiles depends only on injector type (when the solenoid operated injector was tested) while, with piezoelectric injector, it also depends on both energizing time of the injector and injection pressure.

Optical Technique Using Nano-Spark Lightsource for Macro and Microscale Image Acquisition to Study Diesel Spray Atomization

Atomization and fuel-air mixing is an important process in diesel combustion. It directly affects the combustion and emission of diesel engine. Optical technique has the advantage of being unobtrusive in nature when compared to other technique. nanospark unit that has spark duration of 30ns was used as a lightsource to capture high resolution spray image using still film camera. The very short duration of the spark freeze the fast movement of the spray droplet, and sharp image of fuel droplet to be successfully captured by the camera, and then analyzed for sizing and spatial distribution. In addition, by using a more elaborate optical setup, dual image of the same spray can be captured, with a very short time interval between each of them. This provides the means to study dynamic behaviors of the diesel spray and also the droplets, as the progression of the spray and trajectory and velocity of the droplet can be analyze from these images. With the proposed optical technique and optical arrangement, microscopic detail of the diesel engine spray can be captured. Critical data such as droplet sizing can be extracted from this high resolution image. Furthermore, by introducing a more sophisticated optical arrangement coined dual-nano spark photography method, the droplet dynamic behaviors such as flying angle and velocity can be study.

Modeling of Common Rail System and Constant Volume Chamber in Biodiesel Combustion: A Review

Among the challenges faced by diesel engines combustion nowadays are to reduce emission especially Nitrogen Oxide (NOx) and Particular Matter (PM) while enhancing fuel efficiency and power. The purpose of this review is to explore the mixture formation of biodiesel combustion using constant volume chamber and optical visualization. This paper will review the development of a single-shot combustion system and constant volume chamber. An overview of the relation of mixture formation and combustion process in diesel combustion is provided first. This review has shown that the application of Rapid compression Machine (RCM) is used to simulate actual condition especially the injection pressure and air motion. The review also found that the mixing between fuel and air is unavoidable and very important during ignition delay period thus predominantly influences the exhaust emission. The detailed behaviour of injection characteristic that strongly effects the mixture formation especially the spray evaporation and spray interference are discussed.Keywords: Rapid Compression Machine; Ignition Delay; Nozzle; Injection System; Air Motion; Ambient