Combustion Process In Engine Research Articles

Advances in OME fuel technology by combining the designs of engine combustion and chemical processes

Advances in OME fuel technology by combining the designs of engine combustion and chemical processes

Development of a method for experimental investigation of combustion process in lean burn gas engines

The problems of engine experiments in the conditions of unstable combustion were considered. A practical problem was the experimental study of the influence of spark discharge parameters of the ignition system on the operation of the gas engine at the lean limit. The possibility of expanding the lean limits by applying a high-energy capacitor discharge spark ignition system under the condition of limited erosion rate of the spark plug electrode surface was investigated. Particular attention was paid to the instability of the spark discharge as a process of transferring a portion of energy to the mixture in order to develop a flame kernel. After analyzing the results of the experiment, its significant shortcomings associated with the lack of consideration of the phenomenon of cyclic instability of pocesses before ignition of mixture – for example, the spark discharge at the spark plug electrodes were revealed. This fact led to a thorough revision of the experimental research method and formulation of technical requirements to the measuring equipment. A new method of bench tests by applying the latest automated system for the cycle-by-cycle measurement of spark discharge parameters with simultaneous processing of recorded indicator diagrams and statistical analysis of results for the last 1,000 engine cycles was proposed. The main advantage of the method is an increased reliability of the results of the experiment on the lean burn gas engine and reduction of the time for finding experimental errors. Given that this method can be implemented only in a specialized measurement system, functional requirements as part of technical specifications for developing a new measuring system were formed. The results obtained can be used in the experimental studies of combustion in lean burn gas engines at the stage of experiment planning and selection of measuring equipment.

Determination of Combustion Process Model Parameters in Diesel Engine with Variable Compression Ratio

Compression ratio has very important influence on fuel economy, emission, and other performances of internal combustion engines. Application of variable compression ratio in diesel engines has a number of benefits, such as limiting maximal in cylinder pressure and extended field of the optimal operating regime to the prime requirements: consumption, power, emission, noise, and multifuel capability. The manuscript presents also the patented mechanism for automatic change engine compression ratio with two-piece connecting rod. Beside experimental research, modeling of combustion process of diesel engine with direct injection has been performed. The basic problem, selection of the parameters in double Vibe function used for modeling the diesel engine combustion process, also performed for different compression ratio values. The optimal compression ratio value was defined regarding minimal fuel consumption and exhaust emission. For this purpose the test bench in the Laboratory for Engines of the Faculty of Engineering, University of Kragujevac, is brought into operation.

Impact of the laminar flame speed correlation on the results of a quasi-dimensional combustion model for Spark-Ignition engine

In the present study, the impact of the laminar flame speed correlation on the prediction of the combustion process and performance of a gasoline engine is investigated using a 1D numerical approach. The model predictions are compared with experimental data available for full- and part-load operations of a small-size naturally aspirated Spark-Ignition (SI) engine, equipped with an external EGR circuit.A 1D model of the whole engine is developed in the GT-Power™ environment and is integrated with refined sub-models of the in-cylinder processes. In particular, the combustion is modelled using the fractal approach, where the burning rate is directly related to the laminar flame speed.In this work, three laminar flame speed correlations are assessed, including both experimentally- and numerically-derived formulations, the latter resulting from the fitting of laminar flame speeds computed by a chemical kinetic solver.Each correlation is implemented within the combustion sub-model, which is properly tuned to reproduce the experimental performance of the engine at full load. Then, the reliability of the considered flame speed formulations is proved at part-loads, even under external EGR operations.

An indirect in-cylinder pressure measurement technique based on the estimation of the mechanical strength acting on an engine head screw: development and assessment

The increasing application of new concepts for the combustion process in internal combustion engines, e.g. HCCI or RCCI, is mainly aimed at reducing pollutant emissions and fuel consumption. A typical drawback of these technologies is the difficulty of properly controlling the combustion process in the area of medium-high brake mean effective pressure (BMEP), where the thermodynamic conditions inside the cylinder promote a very fast combustion process. To this end, the availability of a fast real-time monitoring of the in-cylinder pressure is then becoming pivotal. This is commonly done by means of piezoelectric dynamic pressure sensors, which are indeed very accurate, but also extremely expensive and characterized by a limited durability due to the harsh working conditions. Moving from this background, the present study describes a new methodology to evaluate the in-cylinder pressure by correlating it with the mechanical stress measured by a strain washer installed on an engine head screw. The strain washer can indeed work in a much more favorable environment with respect to a dynamic pressure sensor flush-mounted on the cylinder head (with aggressive hot gasses and high pressure) with direct benefits for its durability and ease of installation.To assess the model capabilities, experimental tests have been carried out on a single-cylinder, 4-stroke engine and on a 2-stroke engine at the laboratory of internal combustion engines of the Università degli Studi di Firenze. The results reported in the study show the direct comparison of the in-cylinder pressure, as a function of the crankshaft angular position, measured directly with a dynamic pressure sensor and indirectly by means of the strain washer. Sound agreement was found between the two, proving the effectiveness of the proposed methodology.

Development of Tool to Design Piston Bowl Considering Spray Parameters to Reduce Emissions

The piston bowl design is one of the most important factors that affect the air/fuel mixing, combustion and pollutant formation process in a diesel engine. The piston bowl dimensions such as the bowl radius, hitting plane etc… have an effect on combustion process incylinder mixing. This paper aims the development of a tool that can generate the bowl profiles by combining spray parameters. Initially the spray parameters were validated against the engine test data. The bowl geometries generated with same bowl volumes as of the base bowl geometry.lD thermodynamic simulation software Diesel RK is used to predict the performance and emission characteristics of the bowls at full load and part load. The performance parameters such as rated power, Indicated mean effective pressure were compared for all the bowl geometries. Also the emission parameters such as soot and NOx were compared. Best bowl with increased performance and least emissions are selected for the particular engine specification. Increase in performance as well as reduction in soot has been observed with the new bowl geometry.

Intensification of the combustion process in a gasoline engine by adding a hydrogen-containing gas

The results of research on the impact of adding a hydrogen-containing gas obtained by water electrolysis to the air charge of a gasoline engine on the combustion process, the indicator values of the work process, fuel-consumption efficiency and environmental performance of the engine are provided in the paper. The indicator tests of the work process of the engine have been carried out and the key data on the indicator values of the work process of a gasoline engine have been calculated on the base of the obtained indicator-diagrams. It was found that adding a hydrogen-containing gas caused shortening of all phases of combustion and an improvement of the indicator values of the engine. If a hydrogen-containing gas is added to the air charge of a gasoline engine, fuel-consumption efficiency as well as its energy and environmental performance are improved.

Flow and thermal management of engine intake air for fuel and emissions saving

Charge air cooling is the typical technique to reduce temperature of the engine intake air, increasing air density and improving cylinder filling and engine volumetric efficiency in present turbocharged diesel engines. Usually, charge air is cooled by environmental air that crosses a heat exchanger placed in front of the vehicle: its cooling capacity is related to the vehicle speed and other constraints (presence of the main radiator). This leads to an intake air temperature from 30 to 80 °C, depending on engine load, external air conditions and vehicle speed again. If the intake air was more cooled down, the engine volumetric efficiency would be further increased. This can only be done by the use of a dedicated cooling fluid, operating at lower temperature with respect to external air. In this paper, therefore, an evaporator, mounted in parallel with the one of the refrigeration unit used for cabin cooling, was placed on the intake line of a turbocharged diesel engine (F1C IVECO engine), tested on a high speed dynamometer bench: the air refrigeration unit is also composed by a compressor, a condenser and a thermostatic expansion valve. The effects of the undercooling of the charge air have been experimental assessed in terms of fuel consumption and regulated emission reduction, evaluated on the most common engine operating points. Mechanical power demand of the compressor has obviously taken into account in order to assess overall benefits. Achieved net fuel consumption is in the order of 1% at fixed conditions operating the engine as a light duty type, when the intake air sub-cooling is turned on. A benefit on the regulated emissions has been observed (Nitrogen Oxides, Soot) regardless of the setup of the engine combustion processes (injection time, fuel distribution for each injection, Exhaust Gas Recirculated rate). Unburned hydrocarbon and Carbon monoxide behavior, on the other hand, deserves some more attention and call for the re-calibration of the previously cited combustion control parameters.

Simulation of Combustion Process and Pollutant Generation in a PCCI Diesel Engine with Adaptable Multiple Injection

AbstractThe combustion process in a single-cylinder turbocharged diesel engine with a pilot-pilot-main injection strategy was simulated using a computational fluid dynamics software. The effect of ...

Effect of Charge Density on Spray Characteristics, Combustion Process, and Emissions of Heavy-Duty Diesel Engines

In-cylinder charge density at top dead center is an important parameter of diesel engines and is influenced by intake pressure, intake temperature, and compression ratio. The effects of charge density on fuel spray, combustion process, and emissions were investigated by using a constant volume bomb and a heavy-duty diesel engine. Spray development resistance increased with the increase of the charge density in the constant volume bomb. It was found that short spray penetration was accompanied by a large spray cone angle in the former stage with high charge density. However, the equivalence ratio was lowered and the degree of homogeneity of the mixture was increased in the later stage owing to the rapid interaction of fuel and gas at a high mixing rate. Combining the first law of thermodynamics and the second law of thermodynamics for analysis, as the charge density increased, the gross indicated thermal efficiency (ITEg) was improved. However, pumping loss had to be considered with higher charge density. Under this condition, the brake thermal efficiency (BTE) trend was increased initially and decreased subsequently. Under high-load operation (1200 r/min BMEP, 2.0 MPa), the minimum charge density value of 44.8 kg/m3 was found to be reasonable. This charge density was suitable for combustion and brought about minimum exhaust energy and trade-off emissions. Moreover, by analyzing two operation conditions in terms of the maximum BTE with the Miller and the conventional cycles, compression temperature and combustion temperature were reduced in the Miller cycle with the charge density 44.8 kg/m3. A high Cp/Cv could improve the cylinder exergy/power conversion process by its positive effect of increasing the specific heat ratio. Owing to the interaction between a high Cp/Cv and exergy loss to heat transfer, the condition with the minimal charge density could produce more piston work.

An Investigation of the Combustion Process of a Heavy-Duty Natural Gas-Diesel Dual Fuel Engine

This paper investigates the effect of the addition of natural gas (NG) and engine load on the cylinder pressure, combustion process, brake thermal efficiency, and methane combustion efficiency of a heavy-duty NG-diesel dual fuel engine. Significantly increased peak cylinder pressure (PCP) was only observed with the addition of NG at 100% load. The addition of a relatively large amount NG at high load slightly retarded the premixed combustion, significantly increased the peak heat release rate (PHRR) of the diffusion combustion, decreased the combustion duration, and advanced combustion phasing. The accelerated combustion process and increased heat release rate (HRR) at high load were supported by the increased NOx emissions with the addition of over 3% NG (vol.). By comparison, when operated at low load, the addition of a large amount of NG decreased the PHRR of the premixed combustion and slightly increased the PHRR during the late diffusion combustion. Improved brake thermal efficiency was only observed with the addition of a relatively large amount of NG at high load. The improved thermal efficiency was due to a decrease in combustion duration and the shifting of the combustion phasing toward the optimal phasing. The overall combustion efficiency of the dual fuel operation was always lower than diesel-only operation as indicated by the excess emissions of the unburned methane and carbon monoxide from dual fuel engine. This deteriorated the potential of dual fuel engine in further improving the brake thermal efficiency although the combustion duration of dual fuel engine at high load was much shorter than diesel only operation. The addition of NG at low load should be avoided due to the low combustion efficiency of NG and the decreased thermal efficiency. Approaches capable of further improving the in-cylinder combustion efficiency of NG should enable further improvement in the brake thermal efficiency.

Control of the combustion process and emission formation in marine gas engines

A smooth transition to the use of gas engines instead of conventional engines in marine shipping is a logical pathway for compliance with tightening environmental regulations. Currently, five major gas engine concepts are applied in maritime sector. In this paper, a review of the marine gas engine concepts was performed with a focus on the control of combustion and emission. To assess all the contributors to combustion and the emission formation process, three main factors were outlined: design, operational parameters and fuel. The assessment of gas engines was conducted based on these factors. The present paper helps to provide an understanding of the current progress in the development of marine gas engines towards improving of combustion efficiency and reducing the emissions. Moreover, the knowledge gaps, particularly in four-stroke marine high-pressure gas engines, were identified.

Simulation of combustion in a porous-medium diesel engine

The future internal-combustion (IC) engines should have minimum emissions level under lowest feasible fuel consumption. This aim can be achievable with a homogeneous combustion process in diesel engines. We used a porous medium (PM) to homogenize the combustion process. This research studies simulation of a direct-injection diesel engine, equipped with a chemically inert hemispherical PM. Methane is injected into a hot PM, assuming mounted up the cylinder in head. Combustion with lean mixture occurs inside PM. A numerical model of PM engine was carried out using a modified version of the KIVA-3V code. PM results were evaluated with experimental data of unsteady combustion-wave of methane in a porous tube. The results show the mass fraction of methane, CO, NO and temperature in solid and gas phases of the PM and in-cylinder fluid. Also presented are the effects of injection timing and compression ratio on combustion.

Development of a zero-dimensional turbulence model for a spark ignition engine

The necessity for the use of one-dimensional simulation is growing because cost and time required for hardware optimization and optimal calibration of engines based on experiment are increasing dramatically as engines are equipped with growing numbers of technologies. For one-dimensional simulation results to be more reliable, the accuracy and applicability of the combustion model of a one-dimensional simulation tool must be guaranteed. Because the combustion process in a spark ignition engine is driven by the turbulence, many of existing models focus on the prediction of mean turbulence intensity. Although many successes in the previous models can be found, the previous models contain a large number of adjustable constants or require information supplemented from three-dimensional computational fluid dynamics simulation results. For improved applicability of a model, the number of adjustable constants and inputs to the model must be kept as small as possible. Thus, in this study, a new zero-dimensional (0D) turbulence model was proposed that requires information on the basic characteristics of the engine geometry and has only one adjustable constant. The model was developed based on the energy cascade model with additional consideration of following aspects: loss of kinetic energy during the intake stroke, the effect of piston motion during the compression and the expansion stroke, modifications to correlations for integral length scale, geometric length scale, and production rate of turbulent kinetic energy. An adjustable constant to consider engine design which determines tumble strength was also introduced. The comparison of the simulation results with those of three-dimensional computational fluid dynamics confirmed that the developed model can predict the mean turbulence intensity without case-dependent adjustment of the model constant.

Numerical study of the effects of biodiesel unsaturation on combustion and emission characteristics in diesel engine

Biodiesel from different feedstocks has different physicochemical properties. As one of the most important properties, the degree of unsaturation (DU), which is characterized by the number of double bonds in biodiesel composition, could significantly affect its combustion and emission formation process in diesel engines. This study adopted the definition of the degree of unsaturation and aimed to investigate its effect on combustion and emissions in a diesel engine fueled by different biodiesels with different DU. Methyl decanoate (MD), methyl-9-decenoate (MD9D) and n-heptane were adopted as the surrogate fuels to model biodiesel fuels in this study. The different DU in different biodiesel is represented by varying the relative fraction of those three surrogate components when coupling the reaction mechanism into CFD KIVA4-CHEMKIN codes. Numerical modeling was performed to predict the differences in combustion process and the soot, NO and CO emissions in a diesel engine fueled with five typical types of biodiesel under 10%, 50%, and 100% engine loads. The results show that the DU value has a tangible impact on the ignition delay and the emission formation of biodiesel fuels at all engine loads while a negligible impact on the total heat release and the in-cylinder pressure profile at medium-high engine load. The increase of biodiesel unsaturation level alters the viscosity, oxygen contents of fuel, thereby leading to better fuel-air mixing, higher local temperature, and thus promoting the NO emission production while reducing the CO emission. Furthermore, higher unsaturated biodiesel with more carbon double bond also exhibits shorter ignition delay and produces more soot precursor formation, hence more soot emission.

The importance of endothermic pyrolysis reactions in the understanding of diesel spray combustion

The significance of pyrolysis reactions in the early stages of diesel combustion has received little attention in the literature, which warrants a mechanistic investigation of the controlling chemistry along with its potential impacts on the overall combustion process in engines. Experiments were performed in a constant volume vessel to probe these pyrolytic reactions, where diesel fuel sprays were injected into air at varied pressures and temperatures chosen to represent an engine operating at various loads. The pressure inside the vessel was found to decrease immediately following the start of injection before increasing as the exothermic heat release occurs. The initial pressure decrease has been conventionally attributed to an evaporative cooling effect of the diesel spray, but the objective of this paper is to test the hypothesis that endothermic pyrolysis reactions can make a significant contribution to the observed pressure decrease.The addition of 1% of the cetane booster, 2-ethylhexylnitrate (2-EHN), to the fuel was found to shorten the measured ignition delay time, as expected. However the presence of 2-EHN can also increase the magnitude of the initial pressure decrease compared to conventional diesel fuel. Detailed chemical kinetic modeling shows that the effects observed in the constant volume vessel can plausibly be attributed to pyrolysis reactions, and that the addition of 2-EHN to the base fuel enhances their influence. The modelling results also imply that the influence of these pyrolysis reactions increases with increasing temperature, pressure, the alkyl chain length of the base fuel, and the amount of any radical initiator in the fuel.

Determining Parameters of Double-Wiebe Function for Simulation of Combustion Process in Overload Diesel Engine with Common Rail Fuel Feed System

To analyze the peculiarities of the combustion process in an overload diesel engine with the system of Common Rail type with one-stage injection, the indicator diagram was registered. The parameters of the combustion process simulated by the double-Wiebe function were calculated as satisfactorily reconstructing the law of burning rate variation. The main parameters of the operating cycle obtained through the indicator diagram processing and the double-Wiebe function calculation differed insignificantly. And the calculated curve of the cylinder pressure differed notably only in the end of the expansion stroke. To improve the performance of the diesel engine, a two-stage fuel injection was recommended.

A graphic pattern feature-mapping-based data-driven condition monitoring method for diesel engine malfunction identification and classification

Effective condition monitoring of diesel engine can ensure the reliability of large-power machines and prevent catastrophic consequences. Cylinder pressure is capable of reflecting the whole combustion process of diesel engine, and hence can help to identify the malfunctions of the diesel engine during operation. In this paper, a graphic pattern feature-mapping method is proposed for graphic pattern feature recognition in data-driven condition monitoring. The graphic feature extraction and recognition are linked by labeled feature-mapping. It is used for identifying the running condition of the diesel engine via analyzing the cylinder pressure signal of the diesel engine. The different types of the malfunctions which are caused by different parts of the diesel engine such as induction system, valve actuating mechanism, fuel system, fuel injection system, etc. can be identified just by cylinder pressure signal. The bench experiment of a large-power diesel engine is performed to validate this graphic pattern recognition method. The results show that it has good accuracy on multi-malfunction identification and classification when the engine operates at one speed and one load.

Analysis of Combustion Process in Industrial Gas Engine with Prechamber-Based Ignition System

Application of a pre-combustion chamber (PCC) ignition system is one of the methods to improve combustion stability and reduce toxic compounds emission, especially NOx. Using PCC allows the operation of the engine at lean combustion conditions or the utilization of low calorific gaseous fuels such as syngas or biogas. The paper presents the results of an experimental study of the combustion process in two stroke, large bore, stationary gas engine GMVH 12 equipped with two spark plugs (2-SP) and a PCC ignition system. The experimental research has been performed during the normal operation of the engine in an industrial compression station. It was observed that application of PCC provides less cycle-to-cycle combustion variation (more than 10%) and nitric oxide and carbon monoxide emissions decreased to 60% and 26% respectively. The total hydrocarbon (THC) emission rate is 25% higher for the engine equipped with PCC, which results in roughly two percent engine efficiency decrease. Another important criterion of engine retrofitting was the PCC location in the engine head. The experimental results show that improvement of engine operating parameters was recorded only for a configuration with one port offset by 45° from the axis of the main chamber. The study of the ignition delay angle and equivalence ratio in PCC did not demonstrate explicit influence on engine performance.

Emission of volatile organic compounds during combustion process in a miniature turbojet engine

Emission of volatile organic compounds during combustion process in a miniature turbojet engine