Practical Diesel Engine Research Articles

Design of Combustion Control System Based on Adaptive Output Feedback for Premixed Diesel Combustion

Abstract This paper deals with a combustion control system design problem for diesel engines. The consider combustion in this paper is a premixed diesel combustion which produce a dual peak heat release rate. This combustion has high thermal efficiency and low NOx and PM emissions. However, in order to implement this combustion, it is required to design a robust combustion control system because this combustion is low robust with respect to changes of the engine state. Therefore, in this paper, we design an adaptive output feedback control system by considering the in-cylinder heat release rate as the output to be controlled. The effectiveness of the proposed method is confirmed through numerical simulations and experiments on a practical diesel engine.

Improvement of liquid fuel atomization for an internal engine using an auxiliary device

Controlled atomization is essential for reducing soot emission in practical diesel engines. In this work, an auxiliary device called a FAD (fuel activation device) was inserted into the fuel injection line to induce cavitation in the diesel spray. The performance of the FAD was examined in terms of pollutant emissions in a field test as well as aerosol sizes in lab-scale experiments. Experimental results showed that FAD reduced the size distribution of injected droplets and decreased the fuel consumption rate and emission amounts of PM10, CO, and NOx by 42%, 50% and 13.4%, respectively.

An efficient liquid film vaporization model for multi-component fuels considering thermal and mass diffusions

An improved multi-component quasi-dimensional vaporization model for wall film was proposed with considering the finite thermal and mass diffusions within the liquid film. In the improved model, high-order polynomials were introduced to describe the profiles of the temperature and component concentrations within the film. The results show that the predictions from the present quasi-dimensional model agree well with those predicted by the one-dimensional model. By investigating the effect of the thermal and mass diffusions on the vaporization of the diesel film, it is found that the thermal diffusion plays a more dominant role in the multi-component film vaporization. Compared with the linear temperature model with the linear temperature and uniform component distributions in the film, the application range of the quasi-dimensional model is considerably wider and the computational error is significantly reduced. Finally, the linear temperature, quasi-dimensional, and one-dimensional models were integrated into a Computational Fluid Dynamics (CFD) code for the simulations of film vaporization in the flow over a backward facing step and in a practical diesel engine. The results indicate that the improved model gives much better agreement with the one-dimensional solutions than the linear temperature model, while maintaining high computational efficiency under different operating conditions.

Understanding the Relationship between Cetane Number and the Ignition Delay in Shock Tubes for Different Fuels Based on a Skeletal Primary Reference Fuel (n-Hexadecane/Iso-cetane) Mechanism

A new skeletal oxidation mechanism for the primary reference fuel (PRF) was established with a decoupling methodology. The mechanism is composed of n-hexadecane and iso-cetane submechanisms, containing 44 species and 139 reactions. Using the present mechanism, the relationship between cetane number and the ignition delay in shock tubes was investigated. First, based on the ignition delay data in shock tubes, the cetane number of various fuels was estimated using the present PRF mechanism and a weighted least-squares method. The prediction of cetane number investigated in this study primarily focused on the operating conditions of practical diesel engines (i.e., the equivalence ratio of 1.0 and pressures from 19–80 atm), which encompass the cetane number from 15 to 100. Under the test operating conditions, the mean absolute deviation of the predicted cetane number is within 3.327. Furthermore, according the cetane number of different fuels, the ignition delays in shock tubes were reproduced by the present mechanism focusing on a wide range of equivalence ratios (0.5–3.0) and pressures (20–50 atm). The results indicated that the predicted IDs of alkanes were more accurate than those of other types of fuels and blended fuels because of the consistent molecular structure of the n-hexadecane/iso-cetane used in the present mechanism. Because of the compact size of the skeletal mechanism, its application can considerably reduce the computational time for 3D combustion simulations, especially for practical fuels with complicated compositions.

A feasibility study of implementation of oxy-fuel combustion on a practical diesel engine at the economical oxygen-fuel ratios by computer simulation

To help achieve zero carbon emissions from inland waterway vessels, this implementation of oxy-fuel combustion on a practical diesel engine at the economical oxygen-fuel ratios were systematically studied and analysed in this paper. A 1-D simulation was used to explore the effect of various operating parameters for recovering the engine power when the engine is modified to the oxy-fuel combustion from conventional air combustion. The brake power of oxy-fuel combustion is only 26.7 kW that has a noticeable decline compared with 40 kW of conventional air combustion with fixed consumption of fuel and oxygen. By optimising some valuable parameters, like fuel injection timing, intake charge temperature, intake components, engine compression ratio and water injection strategy, a benefit of 6.8 kW has been acquired in the engine power. Afterwards, a remarkable benefit was obtained with the increase of lambdaO2 from 1.0 to 1.5, finally obtaining the same engine power with the conventional air combustion. Above all, taking advantage of various operating parameters, it is expected to further improve the value of the implement of oxy-fuel combustion on diesel engines at the economical oxygen-fuel ratios.

Spray combustion of Jet-A and diesel fuels in a constant volume combustion chamber

This work investigates the spray combustion of Jet-A fuel in an optical constant-volume combustion chamber under different ambient initial conditions. Ambient temperature was varied at 800K, 1000K, and 1200K and five different ambient O2 concentrations were used, spanning 10–21%. These ambient conditions can be used to mimic practical diesel engine working conditions under different fuel injection timings and exhaust gas recirculation (EGR) levels. Both transient and quasi-steady state analyses were conducted. The transient analysis focused on the flame development from the beginning to the end of the combustion process, illustrating how the flame structure evolves with time. The quasi-steady state analysis concentrated on the stable flame structure and compared the flame emissions in terms of spatially integrated intensity, flame effective area, and intensity per pixel. The transient analysis was based on measurements using high-speed imaging of both OH∗ chemiluminescence and broadband natural luminosity (NL). For the quasi-steady state analysis, three flame narrow-band emissions (OH∗ at 310nm, Band A at 430nm and Band B at 470nm) were captured using an ICCD camera. Based on the current Jet-A data and diesel data obtained from previous experiments, a comparison between Jet-A and diesel was made in terms of flame development during the transient state and spatially integrated intensity, flame effective area, and intensity per pixel during the quasi-steady state. For the transient results, Jet-A shares a similar flame development trend to diesel, but featuring a narrower region of NL and a wider region of OH∗ with the increase of ambient temperature and O2 concentration. The soot cloud is oxidized more quickly for Jet-A than diesel at the end of combustion, evident by comparing the area of NL, especially under high O2 concentration. The quasi-steady state results suggest that soot is oxidized effectively under high O2 concentration conditions by the wider region of OH∗ in the downstream locations where only OH∗ emission is observed. The intensity of OH∗ is higher for Jet-A than diesel under low O2 concentration but lower under high O2 concentration. The intensity of NL is higher for Jet-A for all the conditions investigated. However, the intensities of Band A and Band B are lower for Jet-A for all these conditions. Based on the imaging of multiple-band flame emissions, the spray flame structures were further analyzed for the two fuels under both low temperature and conventional combustion modes. Conceptual flame structures were proposed to complement the previous conceptual models for spray combustion under different combustion modes.

First and Second-Law Efficiency Analysis and ANN Prediction of a Diesel Cycle with Internal Irreversibility, Variable Specific Heats, Heat Loss, and Friction Considerations

The variability of specific heats, internal irreversibility, heat and frictional losses are neglected in air-standard analysis for different internal combustion engine cycles. In this paper, the performance of an air-standard Diesel cycle with considerations of internal irreversibility described by using the compression and expansion efficiencies, variable specific heats, and losses due to heat transfer and friction is investigated by using finite-time thermodynamics. Artificial neural network (ANN) is proposed for predicting the thermal efficiency and power output values versus the minimum and the maximum temperatures of the cycle and also the compression ratio. Results show that the first-law efficiency and the output power reach their maximum at a critical compression ratio for specific fixed parameters. The first-law efficiency increases as the heat leakage decreases; however the heat leakage has no direct effect on the output power. The results also show that irreversibilities have depressing effects on the performance of the cycle. Finally, a comparison between the results of the thermodynamic analysis and the ANN prediction shows a maximum difference of 0.181% and 0.194% in estimating the thermal efficiency and the output power. The obtained results in this paper can be useful for evaluating and improving the performance of practical Diesel engines.

A Comprehensive Study of Effects of Mixing and Chemical Kinetic Models on Predictions of n-heptane Jet Ignitions with the PDF Method

The composition Probability Density Function (PDF) model is coupled with a Reynolds-averaged k − e turbulence model and three computationally efficient, yet widely used chemical mechanisms to simulate transient n-heptane spray injection and ignition in a high temperature and high density ambient fluid. Molecular diffusion is modelled by three mixing models, namely the interaction by exchange with the mean (IEM), modified Curl (MC) and Euclidean minimum spanning trees (EMST) models. The liquid phase is modelled by a discrete phase model (DPM). This represents among the first applications of the PDF method in practical diesel engine conditions. A non-reacting case is first considered, with the focus on the ability of the model to capture the spray structure, e.g., vapour penetration and liquid length, fuel mixture fraction and its variance. Reacting cases are then investigated to compare and evaluate the three different chemical mechanisms and the three mixing models. It is concluded that the EMST mixing model in conjunction with a reduced chemical kinetic model (Lu et al., Combust Flame 156(8):1542–1551, 2009) performs the best among the options considered. The sensitivity of the results to the choice of the mixing constant is also studied to understand its effect on the flame ignition and stabilisation. Finally, the PDF model is compared to a well-mixed model that assumes turbulent fluctuations are negligible, which has been widely used in the diesel spray combustion community. Significant structural differences in the modelled flame are revealed comparing the PDF method with the well-mixed model. Quantitatively, the PDF model exhibits excellent agreement with the measurements and shows much better results than the well-mixed model in all ambient O2 and temperature conditions.

Heat transfer effects on the performance of an air-standard irreversible dual cycle

The objective of this study is to analyse the effects of heat transfer loss and internal irreversibilites, resulting from adiabatic processes, on an irreversible diesel heat engine. Thermodynamic optimisation has been carried out based on the Maximum Power (MP), Maximum Thermal Efficiency (MEF) and Maximum mean Effective Pressure (MEP) criteria for the dual cycle. Power output, thermal efficiency and mean effective pressure are obtained by introducing variable compression ratio, inlet temperature, combustion and heat transfer constants, and compression and expansion efficiencies. Optimal performance and design parameters of the dual cycle are obtained numerically for the MP, MEF and MEP conditions. The optimal compression ratio and pressure ratio at MEP conditions are compared with those results obtained by using the MP and MEF criteria for different constants of heat transfer and combustion in the characteristic grid curves. The results obtained in this paper may provide a guide to the performance and improvement of practical diesel engines.

A study on emissions improvement of a diesel engine equipped with a mechanical supercharger

The engine performance and emissions from a 3 l diesel engine equipped with a mechanical supercharger are investigated experimentally, and the advantages and disadvantages of the mechanical supercharger system are discussed in a comparison with performances and emissions from a corresponding 3 l diesel engine equipped with a turbocharger. An experiment conducted under steady-state conditions shows that the mechanical supercharger delivers higher boost pressures than the turbocharger under steady-state low- and middle-load operating conditions, and that the higher boost pressure allows the application of higher amounts of exhaust gas recirculation (EGR), which leads to lower NOx emissions. In a transient test, the fuel flowrate is increased instantly from a low to high rate at a constant engine speed, and T90, which is the time required for the mechanical supercharger to achieve 90 per cent of the steady-state boost pressure, is found to be considerably shortened as compared to T90 obtained in a similar test with a corresponding turbocharged engine. In addition, the Japanese JE05 test result shows that NOx emission from the 3 l engine equipped with the mechanical supercharger is lower by 50 per cent than the engine with the turbocharger at a common level of soot emissions. However, the fuel consumption rate is worsened by 5.5 per cent due to the drive loses of the supercharger. Further study for reducing the fuel penalty is necessary to apply the mechanical supercharger to practical diesel engine systems.

Performance Analysis of a Diesel Cycle under the Restriction of Maximum Cycle Temperature with Considerations of Heat Loss, Friction, and Variable Specific Heats

of the cycle decrease with increasing friction loss. It is noteworthy that the eects of heat loss characterized by a percentage of fuel’s energy, friction and variable specific heats of working fluid on the performance of a Diesel-cycle engine are significant and should be considered in practice cycle analysis. The results obtained in the present study are of importance to provide a good guidance for the performance evaluation and improvement of practical Diesel engines.

Effects of variable specific heat ratio of working fluid on the performance of an irreversible Diesel cycle

SYNOPSIS The effects of the variable specific heat ratio of the working fluid on the performance of a Diesel cycle, with considerations of heat transfer and friction-like term losses, are investigated by using finite time thermodynamics in this paper. The relationships between power output and compression ratio, between thermal efficiency and compression ratio, as well as the optimal relationship between power output and efficiency of the cycle, are derived by detailed numerical examples. The results obtained herein show that the effects of variable specific heat ratio of working fluid on the power output and thermal efficiency of the cycle are significant and should be considered in the design of practical Diesel engines.

Heat transfer effects on the performance of an air standard Dual cycle

There are heat losses during the cycle of a real engine that are neglected in ideal air standard analysis. In this paper, the effects of heat transfer on the net work output and the indicated thermal efficiency of an air standard Dual cycle are analyzed. Heat transfer from the unburned mixture to the cylinder walls has a negligible effect on the performance for the compression process. Additionally, the heat transfer rates to the cylinder walls during combustion are the highest and extremely important. Therefore, we assume that the compression and power processes proceed instantaneously so that they are reversible adiabatics, and the heat losses during the heat rejection process can be neglected. The heat loss through the cylinder wall is assumed to occur only during combustion and is further assumed to be proportional to the average temperature of both the working fluid and the cylinder wall. The results show that the net work output versus efficiency characteristics and the maximum net work output and the corresponding efficiency bounds are strongly influenced by the magnitude of the heat transfer. Higher heat transfer to the combustion chamber walls lowers the peak temperature and pressure and reduces the work per cycle and the efficiency. The effects of other parameters, in conjunction with the heat transfer, including combustion constants, cut-off ratio and intake air temperature, are also reported. The results are of importance to provide good guidance for the performance evaluation and improvement of practical Diesel engines.

舶用ディーゼル機関の初期なじみのシリンダライナ温度

The surface temperature of cylinder liner is one of the factors which affect to the lubrication between cylinder liner and piston rings. Although many works has been conducted with experimental apparatus, few experiments studied with practical diesel engines in pre-running period.In the pre-running period, engine frequently have metal contacts of cylinder liner and piston rings. It is think that the rise of temperature by metal contacts affect to the state of liner-ring lubrication. So the cylinder liner temperature of a marine diesel engine was measured in pre-running period.From experimental results, it was found that the liner temperature of few measurement points changed irregularly at the first glance, but almost were arranged statistically in few forms, and maximum temperature and mode-value ratein the form were more important than mean temperature to estimate the state of the liner-rings lubrication.

IMPINGING DIESEL SPRAY DYNAMICS

A study has been made of the physics of a pulsed diesel spray impacting on a flat plate under atmospheric conditions. Photographs of the impinging diesel spray reveal an impingement region, a liquid buildup region, a ligament region at the edge of the liquid buildup region, and a droplet region near the outer edge of the impinged spray. Two different reatomization mechanisms for the portion of the spray that hits the flat plate are shown to exist. The dominant reatomization mechanism, ligament formation, may not be applicable to a practical diesel engine because of the concave geometry of the piston bowl. A modification of the polarization ratio technique allowed nearly instantaneous measurements of droplet size to be made. Measurements of droplet size show that droplet shattering is the other reatomization mechanism.

Journal Bearings without Circumferential Symmetry under Dynamic Loading

Since the advent of computers, considerable work has been done on the analysis of journal bearings under dynamic loading. Most of this work has been restricted to bearings with circumferential symmetry, since departure from this assumption increases the computation time very severely. Fortunately, this assumption satisfies most of the cases encountered in practice in the field of reciprocating machines, where the majority of bearings have centre circumferential grooves or oil holes in their lightly loaded regions. However, bearings have been proposed with circumferential grooves over part of the circumference and it has previously been difficult to evaluate such designs. This paper describes a new computer programme which takes advantage of the experience gained in earlier work to analyse the performance of journal bearings without circumferential symmetry under dynamic loading. A practical diesel engine design is evaluated and the results are presented. It is found that the programme requires a 40-fold increase in computing time and therefore cannot be economically used as a routine design tool. However, it is shown that the simpler programme, which assumes circumferential symmetry, may be used to put bounds on the performance of such bearings.