High-efficiency Engines Research Articles

The potential of statistical RANS to predict knock tendency: Comparison with LES and experiments on a spark-ignition engine

Pollutant regulations and fuel consumption concerns are the driving guidelines for increased thermal efficiency and specific power in current internal combustion engines. The achievement of such challenging tasks in Spark Ignition units is often limited by the onset of knock, which hinders the possibility to operate the engine with the optimal combustion phasing. The sporadic occurrence of individual knocking events is related to cycle-to-cycle variability of turbulent combustion. This is avoidable by only accepting a safety margin from its earliest onset.On one side, the stochastic nature of knock and turbulence-related combustion variability would indicate Large-Eddy Simulation (LES) as the most appropriate technique for CFD analyses. Nevertheless, Large-Eddy Simulation remains a very time- and CPU-demanding approach, hardly integrated in the industrial timeframe for the design exploration and development of new units. Therefore, Reynolds Averaged Navier Stokes (RANS) models representing the average flow are chosen to limit CPU and development times, though they suffer from the intrinsic inability to account for cycle-dependent phenomena (e.g. knock). This is particularly critical at knock-borderline conditions, where far-from-average knocking events may occur. A previously developed statistical RANS-PDF knock model partly overcomes this limitation using equations for mixture fraction and enthalpy variance, ultimately reconstructing log-normal distributions of knock intensity. This allows RANS simulations to be directly compared to the usual statistical knock analysis at the test-bench.In this paper all the mentioned modelling techniques (LES, RANS and RANS-PDF) are applied to simulate combustion and knock in a currently made turbocharged GDI engine under knock-safe, knock-limited and light-knocking conditions. The study relevance lays in the critical comparison of the results. The full potential of the statistical RANS-PDF model for engine development is highlighted on a coherent basis. The possibility to preserve the RANS formalism while enriching the results with knock statistical description is a relevant advancement in the virtual design of high-efficiency engines.

A Method for Matching Two-Stage Turbocharger System and Its Influence on Engine Performance

Matching of a two-stage turbocharging system is important for high efficiency engines because the turbocharger is the most effective method of exhaust heat recovery. In this study, we propose a method to match a two-stage turbocharging system for high efficiency over the entire range of operational conditions. Air flow is an important parameter because it influences combustion efficiency and heat load performance. First, the thermodynamic parameters of the engine and the turbocharging system are calculated in eight steps for selecting and matching the turbochargers. Then, by designing the intercooler intensity, distribution of pressure ratio, and compressor operational efficiency, it is ensured that the turbochargers not only meet the air flow requirements but also operate with high efficiency. The concept of minimum total drive power of the compressors is introduced at a certain boost pressure. It is found that the distribution of pressure ratio of the high- and low-pressure (LP) turbocharger should be regulated according to the engine speed by varying the rack position of the variable geometry turbocharger (VGT) to obtain the minimum total drive work. It is verified that two-stage turbochargers have high efficiency over the entire range of operational conditions by experimental research. Compared with the original engine torque, low-speed torque is improved by more than 10%, and the engine low fuel consumption area is broadened.

Effect of Injection Parameters: Injection Timing and Injection Pressure on the Performance, Emission and Combustion Characteristics of CRDI Diesel Engine Operate with Palm Oil Methyl Ester (POME)

This experimental study mainly focused on the investigation of CRDI diesel engine powered with palm oil methyl ester (POME) biodiesel and diesel fuels. The Toroidal Re-entrant combustion chamber shape (TRCC) and 6 holes CRDI injector were selected for experiment. The current research engine operated with constant CR 17.5 and speed 1500 rpm. In the first phase of work, the injection timing (IT) varied from -25 °BTDC to 5 °ATDC with interval of 5 degree during the experiments. The injection time-10 °BTDC has been optimized for higher engine efficiency. In the second phase of work, the injection opening pressure (IOP) has been varied form 600 bar to 1000 bar with increment of 100 bar interval during the experiments. The IOP of 900 bar has been optimized with constant fuel IT -10 °BTDC. Finally, the end results of experiments were reported that combined effects of IT (-10 °BTDC) and IOP (900 bar) enhanced the engine output in terms of brake thermal efficiency (BTE), also minimizing the pollutants using TRCC shape and 6-hole CRDI injector for CRDI diesel engine at 80% load.

Development of bondcoats for high lifetime suspension plasma sprayed thermal barrier coatings

Fabrication of thermal barrier coatings (TBCs) by suspension plasma spraying (SPS) seems to be a promising alternative for the industry as SPS TBCs have the potential to provide lower thermal conductivity and longer lifetime than state-of-the-art allowing higher engine efficiency. Further improvements in lifetime of SPS TBCs and fundamental understanding of failure mechanisms in SPS TBCs are necessary for their widespread commercialisation. In this study, the influence of varying topcoat-bondcoat interface topography and bondcoat microstructure on lifetime was investigated. The objective of this work was to gain fundamental understanding of relationships between topcoat-bondcoat interface topography, bondcoat microstructure, and failure mechanisms in SPS TBCs.Seven sets of samples were produced in this study by keeping same bondcoat chemistry but varying feedstock particle size distributions and bondcoat spray processes. The topcoat chemistry and spray parameters were kept identical in all samples. Three-dimensional surface measurements along with scanning electron microscopy images were used to characterise bondcoat surface topography. The effect of varying interface topography and bondcoat microstructure on thermally grown oxide formation, stresses and lifetime was discussed.The results showed that varying bondcoat powder size distribution and spray process can have a significant effect on lifetime of SPS TBCs. Smoother bondcoats seemed to enhance the lifetime in case of SPS TBCs in case of same bondcoat chemistry and similar bondcoat microstructures. When considering the samples investigated in this study, samples with high velocity air-fuel (HVAF) bondcoats resulted in higher lifetime than other samples indicating that HVAF could be a suitable process for bondcoat deposition in SPS TBCs.

High efficient internal combustion engine using partially premixed combustion with multiple injections

Improving the efficiency of the powertrain system is of great importance to reduce the greenhouse gas CO2. Advanced combustion engine with Partially Premixed Combustion (PPC) is one of the best solutions. It is proved to have a high engine efficiency and low emission level. Using multiple injections is a good way to achieve PPC. The efficiencies using multiple injections were evaluated on a metal engine with modern architecture and the reasoning behind that was explored on an optical engine. The metal engine results shown that the point with optimized multiple injections is of higher efficiency than a single injection. Optical results demonstrated that the direct interaction of the first and later injection, as well as the interactions of the fuel and the in-cylinder bulk flow fields and surfaces, could affect mixing and fuel movement and, hence the efficiency. One of the reasons why the optimized multiple injections have a higher efficiency is that the center of the fuel is moved close to the center of the cylinder. Thus, the heat transfer between the heat produced from the fuel-gas mixture and the cylinder liner can be reduced by the isolation. This explains how the injections influence the fuel distribution and the heat transfer and, hence, the engine efficiency.

Effects of flash boiling injection on in-cylinder spray, mixing and combustion of a spark-ignition direct-injection engine

Higher engine efficiency and ever stringent pollutant emission regulations are considered as the most important challenges for today's automotive industry. Fast evaporation and combustion technique has caused unprecedented attention due to its potential to solve both of the above challenges. Flash boiling, which features a two-phase flow that constantly generates vapor bubbles inside the liquid spray is ideal to achieve fast evaporation and combustion inside direct-injection (DI) gasoline engines. In this study, three spray conditions, including liquid, transitional flash boiling and flare flash boiling spray were studied for comparison under cold start condition in a spark-ignition direct-injection (SIDI) optical gasoline engine. Optical access into the combustion chamber includes a quartz linear and a quartz insert on the piston. In separate experiments, we recorded the crank angle resolved spray morphology using laser scattering technique, and distribution of fuel before ignition employing laser induced fluorescence technology, as well as time-resolved color images of flame with high-speed camera. The spray morphology during the intake stroke shows stronger plume-plume and plume-air interaction under flash boiling condition, as well as smaller penetration. Then around the end of compression (before ignition), the fuel distribution is also shown to be more homogeneous with less cyclic variation under flash boiling. Finally, from the color images of the flame, it was found that with the increase of superheat degree, the diffusion rate of blue flame (generated by excited molecules) is higher, which is considered to be related with the larger fractal dimension of the flame front. Also, the combustion is more complete with less yellow flame under flash boiling.

A simplified CFD model for spectral radiative heat transfer in high-pressure hydrocarbon–air combustion systems

Detailed radiation modeling in piston engines has received relatively little attention to date. Recently, it is being revisited in light of current trends towards higher operating pressures and higher levels of exhaust-gas recirculation (EGR), both of which enhance molecular gas radiation. Advanced high-efficiency engines also are expected to function closer to the limits of stable operation, where even small perturbations to the energy balance can have a large influence on system behavior. Detailed radiation modeling using sophisticated tools like photon Monte Carlo/line-by-line (PMC/LBL) is computationally expensive. Here, guided by results from PMC/LBL, a simplified stepwise-gray spectral model in combination with a first-order spherical harmonics (P1 method) radiative transfer equation (RTE) solver is proposed and tested for engine-relevant conditions. Radiative emission, reabsorption and radiation reaching the walls are computed for a heavy-duty compression-ignition engine at part-load and full-load operating conditions with different levels of EGR and soot. The results are compared with those from PMC/LBL, P1/FSK (P1 with a full-spectrum k-distribution spectral model) and P1/Gray radiation models to assess the proposed model’s accuracy and computational cost. The results show that the proposed P1/StepwiseGray model can calculate reabsorption locally and globally with less than 10% error (with respect to PMC/LBL) at a small fraction of the computational cost of PMC/LBL (a factor of 30) and P1/FSK (a factor of 15). In contrast, error in computed reabsorption by the P1/Gray model is as high as 60%. It is expected that the simplified model should be broadly applicable to high-pressure hydrocarbon–air combustion systems, with or without soot.

Study of Egyptian castor biodiesel-diesel fuel properties and diesel engine performance for a wide range of blending ratios and operating conditions for the sake of the optimal blending ratio

Egyptian Castor raw oil has been used to produce Castor Methyl Ester (CME) biodiesel utilizing Transesterification-ultrasonic process. To meet the ASTM requirements, CME was blended with the conventional diesel fuel for improving sooting tendency and fuel viscosity. Thermal analysis showed that CME has comparable end-boiling temperature and fuel-air mixing of the diesel fuel. Experiments on a single-cylinder engine in accordance to G-2 of ISO 8718 standard were conducted at wide ranges of blending ratios and operating conditions. Comparing to the neat diesel fuel data, the results of testing CME biodiesel fuel showed that (i) a maximum increase of 8% in the brake specific energy consumptions was received at a blending ratio of 30%, (ii) a slight increase in the brake thermal efficiency (around 1%) was obtained at a blending ratio of 20%, (iii) the best reduction in the carbon monoxide emission (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx) were 17%, 40%, and 0.05%, respectively as recorded at a blending ratio of 10%, (iv) the best reduction of 7.5% in carbon dioxide emissions was observed at 20% blending ratio, and (v) the minimum opacity level was observed at a blending ratio of 30%. The results conclude that the 20% blending ratio is recommended to keep high engine efficiency without environmental deterioration.

Architecture Optimization of Hybrid Electric Vehicles with Future High-Efficiency Engine

The great development of engine technologies can help to improve the engine characteristics and performance: a better thermal efficiency and an extending fuel economy area, which will subsequently decrease the fuel consumption and thus influence the overall architecture of the vehicle. In this paper, an investigation is carried out to assess the influence of the high-efficiency engine on the transmission gear numbers. First, according to the relevant studies and the integration of the advanced engine technology, a future engine fuel consumption map is obtained, based on which, the preliminary simulations are applied to explore the best match between the transmission and the proposed future engine from the perspective of fuel consumption. The simulation results indicate that the transmission with four gears is the best option to match the future engine while maintaining good fuel economy and meeting the driving demands. Then, based on this conclusion, a new hybrid powertrain architecture, which includes four gears for the engine, is introduced and analyzed in detail, with the advantage of seamless gear shift due to the compensation torque of the motor. Finally, to further examine the fuel economy and gear shift quality of the proposed powertrain, the dynamic model is established and the simulation results demonstrate that the new powertrain architecture shows a good fuel consumption performance and the gear shift process can be achieved without power interruption.

Effect of fuel injection characteristics on the performance of a free-piston diesel engine linear generator: CFD simulation and experimental results

The free-piston diesel engine linear generator (FPDLG), as a novel energy conversion device, is investigated by many researcher groups. The injection characteristics are important for the FPDLG operation performance. Therefore, the effects of fuel injection characteristics on the FPDLG are researched by CDF simulation and experimental results in this paper. According to the results, it is found that the trends of the compression ratio and the peak in-cylinder pressure vs the injection timing are the identical with convex function curves. And the IMEP of the FPDLG also show the same trend. Although the heat-release rises in the rapid combustion period, the IMEP vs the injection timing various law present convex function curve on account of reduced heat-release in the normal combustion period. Four injection rate-profiles, i.e. rectangle, wedge, trapezium and triangle are simulated and compared. It is observed that the combustion process with the trapezium rate-profile curve is smoother. The peak in-cylinder pressure and the thermal efficiency can be kept high value while the center of heat-release curve near the TDC. Therefore the trapezium rate-profile is suggested is appropriate and can keep high efficiency of the FPDLG in order to get high engine efficiency.

Effect of combined hole configuration on film cooling with and without mist injection

Turbine blades operate under a harsh environmental condition, and the inlet temperature of gas turbines is increasing with requirement of high engine efficiency. Some cooling schemes are adopted to prevent these blades from the thermal erosion of the hot mainstream. Film cooling technology is used widely and effectively in gas turbines. The coolant air is suppressed to the wall by the main-stream after jetting out of the film hole. A new hole configuration is first pro-posed to improve the film cooling characteristics in this paper. Comparison be-tween a conventional cylindrical hole and a new combined hole is conducted by CFD, and effects of various blowing ratios and droplet sizes are also investigated. Results show that the combined hole configuration provides a wider coverage than that in the cylindrical hole configuration case at high blowing ratios (M = 1.0 and M = 1.5). In addition, the film cooling with mist injection also provides a significant enhancement on cooling performance especially for the combined hole case with a small droplet size (10?5 m).

Partially Premixed Combustion (PPC) Stratification Control to Achieve High Engine Efficiency

Partially premixed combustion (PPC) is a hybrid combustion of Homogeneous Charge Compression Ignition (HCCI) and Diesel Combustion (DC), which has a great potential in reducing the fuel consumption. PPC has a longer premixed time than DC but lesser than HCCI. Therefore it is more stratified than HCCI. This paper first presents results on how the stratification using multiple injections and different EGR influence the efficiency and proposes a control framework for PPC stratification control inspired from the experiments. The control framework is validated in transient operations. Results in both steady and transient operations demonstrated that the more stratified PPC with multiple injections has a lower fuel consumption.

High Efficient Engine Development—Application of Measurement Technique to Engine Development Process—

High Efficient Engine Development—Application of Measurement Technique to Engine Development Process—

Fuel consumption assessment of an electrified powertrain with a multi-mode high-efficiency engine in various levels of hybridization

Powertrain electrification including hybridizing advanced combustion engines is a viable cost-effective solution to improve fuel economy of vehicles. This will provide opportunity for narrow-range high-efficiency combustion regimes to be able to operate and consequently improve vehicle’s fuel conversion efficiency, compared to conventional hybrid electric vehicles. Low temperature combustion (LTC) engines offer the highest peak brake thermal efficiency (BTE) reported in literature, but these engines have narrow operating ranges. In addition, LTC engines have ultra-low soot and nitrogen oxides (NOx) emissions, compared to conventional compression ignition and spark ignition (SI) engines. In this study, an experimentally developed multi-mode LTC-SI engine is integrated into a parallel hybrid electric configuration, where the engine operation modes include homogeneous charge compression ignition (HCCI), reactivity controlled compression ignition (RCCI), and conventional SI. The powertrain controller is designed to enable switching among different modes, with minimum fuel penalty for transient engine operations. A pontryagin’s minimum principal (PMP) methodology is used in the energy management supervisory controller to study a multi-mode LTC engine in parallel HEV architecture with various hybridization levels. The amount of torque assist by the e-motor can change the LTC mode operating time, which leads to variation in the vehicle’s fuel consumption. The results for the urban dynamometer driving schedule (UDDS) driving cycle show the maximum benefit of the multi-mode LTC-SI engine is realized in the mild electrification level, where the LTC mode operating time increases dramatically from 5.0% in a plug-in hybrid electric vehicle (PHEV) to 20.5% in a mild HEV.

The influence of high efficiency engines and hybrids on exhaust systems

Increased efficiency of the combustion process itself and low losses in the Engine, lead to lower temperatures in the exhaust line. Combined with the exhaust gas energy recovery as well as the hybridization of the drivetrain, this temperature decrease will require additional efforts for the exhaust gas aftertreatment in future. Current technologies like SCR with urea could only be used in future with additional heating elements or will need to change to different catalysts or gaseous Ammonia, to keep the current efficiency and conversion rates. Catalyst and filter elements with ultra-low backpressure creating additional new challenges for the correct and robust diagnostics of these aftertreatment components and all emission relevant parts and thresholds. New technologies are needed like the direct measurement of the DPF soot loading with radio frequencies or NH3 sensors to precisely control the ammonia slip for high conversion rates of SCR catalysts.

Maximum efficiencies for internal combustion engines: Thermodynamic limitations

The thermodynamic limitation for the maximum efficiencies of internal combustion engines is an important consideration for the design and development of future engines. Knowing these limits helps direct resources to those areas with the most potential for improvements. Using an engine cycle simulation which includes the first and second laws of thermodynamics, this study has determined the fundamental thermodynamics that are responsible for these limits. This work has considered an automotive engine and has quantified the maximum efficiencies starting with the most ideal conditions. These ideal conditions included no heat losses, no mechanical friction, lean operation, and short burn durations. Then, each of these idealizations is removed in a step-by-step fashion until a configuration that represents current engines is obtained. During this process, a systematic thermodynamic evaluation was completed to determine the fundamental reasons for the limitations of the maximum efficiencies. For the most ideal assumptions, for compression ratios of 20 and 30, the thermal efficiencies were 62.5% and 66.9%, respectively. These limits are largely a result of the combustion irreversibilities. As each of the idealizations is relaxed, the thermal efficiencies continue to decrease. High compression ratios are identified as an important aspect for high-efficiency engines. Cylinder heat transfer was found to be one of the largest impediments to high efficiency. Reducing cylinder heat transfer, however, is difficult and may not result in much direct increases of piston work due to decreases of the ratio of specific heats. Throughout this work, the importance of high values of the ratio of specific heats was identified as important for achieving high thermal efficiencies. Depending on the selection of constraints, different values may be given for the maximum thermal efficiency. These constraints include the allowed values for compression ratio, heat transfer, friction, stoichiometry, cylinder pressure, and pressure rise rate.

Effect of intake manifold water injection on a natural gas spark ignition engine: an experimental study

Design and development of gas CHP (combined heat and power) engines are strongly influenced by the progressively more severe European NOx emissions normative. Water injection represents a promising approach to reduce these emissions while attaining high engine efficiency. In this work, the effect of intake manifold water injection on combustion parameters and performance of a single-cylinder naturally aspirated natural gas spark ignition engine is presented. First, the most appropriate injector was selected, using a spray test bed. Subsequently, engine experiments at constant indicated mean effective pressure (IMEP) and engine speed were conducted with water-fuel ratios of 0.1 to 0.3. IMEP was kept constant at about 6.3 bar by adjusting both air-fuel ratio and spark timing. A NOx reduction of 0.2 g/kWhi (15 %) for a constant ISFC of about 204 g/kWhi was achieved. In the low NOx regime, water injection allows for an improvement of the NOx-ISFC trade-off, while leading to poor fuel consumption at same NOx in the high efficiency regime. Furthermore, water injection implies a reduction of intake mixture temperature, lengthened burning delay and combustion duration and a moderate increase of combustion instability.

The Influence of Diesel Oil Improvers on Indices of Atomisation and Combustion in High-Efficiency Engines

Abstract The process of fuel combustion in a diesel engine is determined by factors existing during liquid fuel injection and atomisation. The physicochemical properties of the fuel to a large extent decide upon the quality of this phase of cylinder fuelling. So it is important to ensure appropriate properties of a fuel affecting its atomisation and, as a result, combustion. The paper deals with the topic of diesel oil improvers and the analysis of their influence on atomisation and combustion indices. In the studies base diesel oil and a diesel fuel improved by a package of additives, were used. The process of conventional and improved fuel injection was analysed by using optical examinations. The amount of released heat was evaluated during the studies carried out on combustion. Significant aspects of the applied improvers in relation to fuel injection and its combustion have been indicated.

The use of different types of piston in an HCCI engine: A review

Homogenous charge compression ignition (HCCI) combines the advantages of spark ignition (SI) and compression ignition (CI) engines to improve fuel consumption and emission levels. HCCI engines have the advantage of relatively higher engine efficiency than SI engines while maintaining lower emissions levels than CI engines. Combustion in HCCI engines occurs spontaneously at any location once the fuel-air mixture reaches its chemical activation energy. Pistons have a major effect on controlling the combustion inside the combustion chamber of an HCCI engine. Many researchers have studied various designs for pistons to improve HCCI engines. The aim of this study is to explore these different types of pistons and their designs in terms of improving the performance of HCCI engines fuelled with gasoline. The most common pistons used in HCCI are two-stroke pistons, bowl types, specialised pistons, and dome-shaped pistons; each offers distinct advantages and disadvantages. Software simulation is the latest way of determining the best piston to be used for HCCI engines, as it is more cost effective and less time consuming than experiments. Overall, bowl type pistons offer reduced fuel consumption and a higher load capacity when used in an HCCI engine.

Quasi-Dimensional Diesel Engine Combustion Modeling With Improved Diesel Spray Tip Penetration, Ignition Delay, and Heat Release Submodels

Increasingly stringent fuel economy and CO2 emission regulations provide a strong impetus for development of high-efficiency engine technologies. Diesel engines dominate the heavy duty market and significant segments of the global light duty market due to their intrinsically higher thermal efficiency compared to spark-ignited (SI) engine counterparts. Predictive simulation tools can significantly reduce the time and cost associated with optimization of engine injection strategies, and enable investigation over a broad operating space unconstrained by availability of prototype hardware. In comparison with 0D/1D and 3D simulations, Quasi-Dimensional (quasi-D) models offer a balance between predictiveness and computational effort, thus making them very suitable for enhancing the fidelity of engine system simulation tools. A most widely used approach for diesel engine applications is a multizone spray and combustion model pioneered by Hiroyasu and his group. It divides diesel spray into packets and tracks fuel evaporation, air entrainment, gas properties, and ignition delay (induction time) individually during the injection and combustion event. However, original submodels are not well suited for modern diesel engines, and the main objective of this work is to develop a multizonal simulation capable of capturing the impact of high-injection pressures and exhaust gas recirculation (EGR). In particular, a new spray tip penetration submodel is developed based on measurements obtained in a high-pressure, high-temperature constant volume combustion vessel for pressures as high as 1450 bar. Next, ignition delay correlation is modified to capture the effect of reduced oxygen concentration in engines with EGR, and an algorithm considering the chemical reaction rate of hydrocarbon–oxygen mixture improves prediction of the heat release rates. Spray and combustion predictions were validated with experiments on a single-cylinder diesel engine with common rail fuel injection, charge boosting, and EGR.