Multiple Injection Strategies Research Articles

Effect of multiple injection optimization on combustion characteristics of low-pressure EGR system engine

Abstract In recent years, reducing oil consumption and pollutant discharge in transportation industry has become an important measure to alleviate energy crisis and environmental pollution. Therefore, the fuel economy and emission characteristics of the engine have become an important index to evaluate the quality of an engine, so EGR technology has gradually become the standard of gasoline engines. But EGR is not always good. In order to alleviate the adverse effects of EGR on combustion, further research on engine combustion is needed. In order to study the effect of multiple injection strategy on engine combustion characteristics, this paper takes a high pressure direct injection gasoline engine equipped with low pressure EGR system as the research object, and verifies the designed multiple injection strategy on special test equipment. A large amount of combustion data of the engine under the same load, different fuel injection stages and fuel injection ratios were collected. By comparing the evaluation indexes of main pollutant emission, fuel consumption and combustion stability, it is found that with the increase of injection times, the combustion characteristics and knock of the engine show a trend of improvement. After using multiple injection strategies at 2000r/min, it can be seen that the optimized injection strategy has better emission characteristics and lower fuel consumption lower knock intensity than that before the injection mode optimization without affecting the power performance.

A comprehensive investigation of injection strategies for improving diesel engine combustion under cold start development

Starting at cold temperatures ranging from -30°C to 0°C has been a concern for all diesel engines, especially for future diesel engines that need to meet tighter carbon emission standards. Combustion instability and increasing smoke emissions are rising concerns during the cold start of diesel engines. Cold ambient conditions cause long cranking periods or complete misfire events in diesel engines; therefore, they produce a large proportion of pollutants within the cylinder due to incomplete combustion. In this study, a comprehensive investigation of multiple injection strategies was conducted under cold-start conditions to identify an optimal injection strategy that improves diesel combustion stability, cold-startup performance, and decreases white smoke emissions at cold ambient temperatures. This study found that cold start-up performance can be improved by eliminating misfire and lowering time to clean up white smoke with a three-injection strategy (two pilots and one main injection, simply named Pilot-Pilot-Main).

Influence of dwell time on the hydraulic behaviour utilizing multiple injection strategies and a piezoelectric diesel injector

The electric dwell time is defined as the duration between two electric pulse signals. It is a crucial parameter when multiple injection strategies are employed. The influence of electric dwell time on the hydraulic behaviour utilizing pilot injection strategy, split injection strategy, post injection strategy and a commercial piezoelectric diesel injector has been analysed experimentally. To do so, a sweep of electric dwell time from 1.15 ms up to 3 ms in all multiple injection strategies using rail pressures of 80, 100 and 120 MPa, and a back pressure of 5 MPa was performed. A fuel mass of 110 mg was injected in all cases analysed employing operating conditions defined from the characteristics curves of injected mass. The hydraulic behaviour was characterized through to measure the first and second hydraulic delay at opening and closing injector, the pressure oscillations generated during the first injection event, and injected fuel mass during second injection event in an injection discharge curve indicator, which is based on the Bosch tube method. In summary, the paper concludes that the hydraulic dwell time depends on the injected mass during the first injection event, and the dynamic response of injector. Moreover, a short electric dwell time causes an increase of injected fuel mass during second injection event, which can be attributed to combine two effects provoked by overlapping the first and second mass flow rate signals, namely, a reduction in the hydraulic delay at opening injector, and an increase in the hydraulic delay at closing injector. Finally, the present research provides information which can be employed to optimization the modulation of injection rate in a diesel engine.

Experimental investigation on spray and flame characteristics of a marine diesel engine with single and double injection

Multiple injection is one of the advanced technologies employed in modern diesel engines to improve combustion efficiency, reduce pollutant emissions, and minimize combustion noise. The application of multiple injection in marine diesel engines differs from its use in vehicles or heavy-duty engines, as it is not commonly combined with Exhaust Gas Recirculation (EGR). However, there is a scarcity of studies specifically examining the combustion characteristics of medium-speed marine diesel engines utilizing multiple injection. Given the large space scale of marine diesel engine, a constant volume chamber with a visible diameter of 240 mm was used, and an injector with a nozzle diameter of 0.465 mm was employed in the experiment. The spray development and combustion process were recorded by Mie-scattering and flame natural luminosity imaging respectively. Both conventional and double injection combustion processes were analyzed in detail. The results show that although the liquid phase spray does not fully penetrate to the cylinder wall in marine diesel engines, the flame penetrates to the cylinder wall rapidly, the flame burns near the wall almost throughout the entire combustion duration. The combustion characteristics of the double injection are significantly different, the flame propagation speed of the pilot and main injection fuel is one-third to one-half of that of a single injection with a long duration. For single injection spray with long injection duration, the flame penetration velocity is determined by the sequential ignition velocity of the fuel. While the flame penetration velocity for sprays with short injection duration mainly depends on the jet penetration velocity. The investigation on the impact of dwell time, fuel distribution, and injection pressure on the combustion process of double injection also provides valuable insights for optimizing multiple injection strategies.

Study Evaluates CO2 Storage Potential During CO2 Mobility-Control Optimization

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 212969, “Evaluation of CO2 Storage Potential During CO2 Mobility-Control Optimization for Enhanced Oil Recovery,” by Alvinda Sri Hanamertani, SPE, Ying Yu, SPE, and Omar El-Khatib, SPE, University of Wyoming, et al. The paper has not been peer reviewed. _ CO2 mobility control through foam technology has enabled better sweep efficiency and, consequently, better oil productivity during enhanced oil recovery (EOR) processes. Along with enhancing oil production, a sound potential exists for in-situ generated foam to enhance CO2 storage. However, the effect of the different in-situ foam generation strategies on the combined goal of maximum oil production and carbon storage is not well elucidated in the literature. In the complete paper, the authors methodically evaluate the simultaneous optimization of CO2 storage and oil recovery using multiple injection strategies. Introduction The current investigation is a continuation of two previous studies that provided a methodology for screening and using foaming agents for optimized CO2 storage in sandstone and carbonate formations. A base case of tertiary CO2 flooding was established for comparison with in-situ foam generation by two approaches: single-cycle surfactant-alternating-gas (SAG) flooding and coinjection of CO2 and surfactant. Additionally, the effect of surfactant concentration on foam efficiency, CO2 storage capacity, and oil recovery were evaluated in both approaches at reservoir conditions. Materials and Methods Fluids and Porous Medium. In this study, a synthetic brine with total dissolved solids of 20 wt% was used as blank brine and laden with a commercial zwitterionic surfactant that was used to prepare surfactant solutions with concentrations of 0.5 and 1 wt% active matter in the synthetic brine. Three core plugs were drilled from an Indiana limestone outcrop block. The cores were then cleaned and oven-dried at 95°C. Experimental Procedure. Vacuum saturation with brine was commenced for the three cores. The porosity of the cores was calculated using their dry and brine-saturated weights. Then, the 100% brine-saturated core was placed in a core holder and loaded into an oven set to 90°C. The pore pressure was fixed at 2,000 psi, and the confining pressure was controlled at 3,000 psi throughout the flooding experiment. The brine permeability of the core samples was evaluated by measuring the pressure drop across the core at different brine-injection flow rates. In the first experiment (IL1), oil drainage with a flow rate of 0.2 cm3/min was performed to establish irreducible water saturation of 46.9%. This total flow rate was kept the same throughout the three experiments. Then, a waterflooding stage was begun and the oil recovery was recorded. After reaching a plateau in oil recovery, supercritical CO2 (scCO2) was injected during the EOR process until the oil production plateaued.

Investigations on Multiple Injection Strategies in a Common Rail Diesel Engine Using Machine Learning and Image-Processing Techniques

<div>The present study examines the effect of the multiple injection strategies in a common rail diesel engine using machine learning, image processing, and object detection techniques. The study demonstrates a novel approach of utilizing image-processing tools to gain information from heat release rates and in-cylinder visualizations from experimental or computational studies. The 3D CFD combustion and emission predictions of a commercial code ANSYS FORTE© are validated with small-bore common rail diesel engine data with known injection strategies. The validated CFD tool is used as a virtual plant model to optimize the injection schedule for reducing oxides of nitrogen (NO<sub>x</sub>) and soot emissions using an apparent heat release rate image-based machine learning tool. A methodology of the machine learning tool is quite helpful in predicting the NO–soot trade-off. This methodology shows a significant reduction in soot and NO emissions using a pilot–main–post-injection schedule of 25% pilot, 25% post-, and 50% main injection, compared to a baseline pilot–main injection schedule. In addition, this work attempts a robust and high-fidelity optimization of the fuel injection schedule using the random forest algorithm for predicting the NO and soot emissions using 73 simulations done with different pilot–main and pilot–main–post-injection strategies on a small-bore diesel engine. Further, the object detection algorithm is trained on simulation data from the small-bore engine for detecting the interaction between the developed combustion from the pilot or main with sprays of subsequent injections using in-cylinder 3D CFD simulation and experimental data. A small-bore engine dataset shows that the trained object detection algorithm successfully corroborates the simulation and experimental data interaction. This investigation, therefore, presents a novel application of object detection methodology by automating the process and providing a general-purpose object detection algorithm. This approach can be used on any new simulation or experimental data for automated detection of the spray–thermal zone interaction without human intervention.</div>

Experimental characterization of the injected mass variation in a high-pressure GDI injector operating with a multiple injection strategy

Increasingly stringent limits to pollutants released by Internal Combustion Engines pushed the automotive research to develop technologies to reduce fuel consumption and emissions. Higher injection pressures are beneficial to accelerate the atomization phase, reducing the particulate matter and unburned hydrocarbon emissions. However, the spray protrusion inside the combustion chamber is enhanced and, consequently, the generation of a thick wall film, which tends to increase the latter emissions. Thus, multiple-injection strategies might be beneficial for both the atomization rate and the spray penetration, owing to a stratified charge inside the chamber. This paper investigates the effect of the adoption of multiple-injection strategies on the behaviour of a GDI injector operating in high injection pressure conditions. The resulting injected mass is influenced by electrical phenomena on the excitation circuit, which mainly depend on the relative time between the end of the first injection and the start of the following. Hence, the total amount of fuel injected with the multiple-injection pattern will differ from its nominal value. In this work, a specific experimental layout was developed to characterize the behaviour of the injector in different operating conditions and quantify the deviation between actual and nominal injected mass. The impact of the magnetized coils on the overall injected mass has been captured referring to the modification of the shape of the driving current profile with respect to the nominal one. Then, a correlation which considers the electric charge variation on the coils has been implemented to model the phenomenon and, consequently, to counterbalance the electro-magnetic effect on the injected mass. The resulting strategy successfully allowed to reduce the difference between the actual and target fuel mass from up to 30% to almost 5%, owing to its implementation on the injection control system to automatically correct the injection commands and compensate the fuel mass deviations.

Improving the lean burn performance of a high compression ratio methanol engine by multiple-injection

Methanol is a promising fuel for achieving carbon neutrality in sectors requiring internal combustion engines. The multiple-injection approach is effective in reducing cycle-to-cycle variations and improving the performance of methanol engines under lean burn conditions. This study proposes a concept for transforming diesel engines into methanol engines with flexible injection and lean burning capabilities. This study fills the research gap in the study of lean methanol combustion in swirl combustion chambers. The effects of 22 different multiple-injection strategies on combustion characteristics, emission performance, and combustion stability are experimentally assessed in a direct-injection spark ignition engine with an excess air ratio (λ) of 1.35. Each multiple-injection strategy is comprehensively evaluated using a merit function and compared with the baseline case that uses single injection. The results show that the double- and triple-injection strategies substantially shorten the durations of combustion and flame development. Therefore, a higher effective expansion ratio is obtained. Meanwhile, the cycle-to-cycle variation in the IMEP decreases from 4.2% of the baseline to 1.49% at T8. CO and HC emissions deteriorate; however, NOx and CO2 emissions under triple injection are lower than those under the baseline. The T7 case with triple injection achieves the highest thermal efficiency, which is 6.8% higher than that for the baseline case. Overall, triple injection achieves higher merit function values, which indicates a better capability to improve lean-burn performance than double injection.

An innovative method of ammonia use in a light-duty automotive diesel engine to enhance diesel combustion, performance, and emissions

This study investigated the novel method of ammonia use in a light-duty automotive diesel engine. An emulsification technique and ammonia solution are combined and adopted to prepare ammonia solution in diesel emulsion referred to as emulsified diesel-ammonia solution (EDAS) and tested under similar diesel combustion conditions. The ammonia solution concentration in EDAS was fixed as 10% by volume (EDAS10) with 2% v/v of surfactant to avoid excessive ammonia slip, corrosive effects, and oxides of nitrogen (NOx) formation. The aim of this study is to explore the effect of presence of hydrogen in EDAS10 on the diesel combustion process under high-pressure multiple injection strategies. Experiments were performed at low, medium, and high loads at the same combustion phasing (CA50) and total energy input as that of diesel to investigate the influence of EDAS10 on combustion, performance, and emissions. The start of injection of EDAS10 and exhaust gas recirculation rate was varied to attain the CA50. The combustion results showed that the EDAS10 blend had increased the heat release rate in the premixed combustion phase with shortened duration and decreased the heat release rate in the diffusion combustion phase compared to neat diesel operation. Double and triple injection of EDAS10 blend also increased the indicated and brake thermal efficiencies by about 4–7% than neat diesel operation. A decrease in 50–67% unburnt emissions, 8–13% decrease in smoke, and 7–19% increase in NO emissions, 2–10% increase in CO2emissions were observed with EDAS10 when compared to diesel operation.

Experimental study on wall heat transfer from diesel spray flame in two-dimensional combustion chamber operated with rapid compression and expansion machine (RCEM)

Heat transfer phenomenon in internal combustion diesel engine is one of problems to be solved. This study was conducted to investigate the relationship between diesel spray impingement, combustion processes, and heat loss using a rapid compression and expansion machine (RCEM). Furthermore, spray combustion and heat transfer processes were investigated using multiple injection strategies with a 6-holes injector. The amounts of diesel fuel used in the pilot, pre-injection, and main injection sprays were 3.964, 0.747, and 11.205 mg, respectively. Variations in common rail pressure conditions (30, 120, and 180 MPa) were applied to properly investigate spray evaporation, air–fuel mixture formation, and heat transfer in the combustion chamber. In addition, a local wall heat flux sensor was installed in the cylinder (head and liner) and piston cavity (upper lip, lip, and bottom) to measure the heat flux distribution, and a diffused backlight illumination method was used to visualize the spray and flame behavior in the combustion chamber and 2D piston cavity. The results showed that the impingement flame surrounding the cylinder head contributed to the highest magnitude and longest duration of the heat flux on the cylinder side owing to the spray flame velocity, impingement, and residence time. Meanwhile, the highest different temperature at cavity bottom induced more heat flux on the cavity side than that on the squish side. In addition, the higher injection pressure increased the spray momentum and spray tip penetration which led to a better air–fuel mixture, better evaporation rate, and less flame residence that contributed to reduce the accumulated heat loss in combustion chamber. Furthermore, a low common rail pressure was found to induce a greater difference in the accumulated heat flux ratio than a high common rail pressure which is owing to longer flame residence time in the combustion chamber. They were approximately 14% and 6% greater than that compared to the baseline common rail pressure which mean that a high common rail pressure contributes for the improving thermal efficiency in spray combustion.

A rate-of-injection model for predicting single and double injection with or without fusion.

Models used to predict the instantaneous injected fuel mass are of varied interest in automotive applications, including for providing inputs to CFD calculations or for engine control. While multiple injection strategies are now commonly used in diesel engines, the overall approach may be susceptible to injection fusion, which is defined as two successive injections that are partly or totally coupled due to the short time interval between each event. In this work, a new model to predict the instantaneous mass flow rate from a diesel injector is proposed based on the analytical solution of a first-order linear dynamic system exposed to an impulsion. Experiments are also conducted to quantify the main injection characteristics of a solenoid indirect-action injector under different injection pressures, backpressures and injection durations, representing a total of 33 different conditions. From these results, a model is proposed and validated against experimental data using a single injection strategy. Then, the model is enhanced to predict split injection with and without injection fusion. Successful comparisons are realized between the model and the experiment. The model is then used to successfully simulate a piezoelectric injector experiencing different levels of fusion available in the literature so as to illustrate the universality of the proposed approach.

Experimental study on diesel spray combustion and heat transfer characteristics with multiple injection strategies by means of rapid compression and expansion machine

A comprehensive investigation was carried out to understand diesel spray combustion processes and heat transfer by applying multiple injection strategies. Experiments were conducted under different injection pressure conditions ranging from 30 MPa to 180 MPa, and the results clarified the capability of high injection pressure to facilitate spray evaporation and distribution in detail. It also demonstrated that the local heat flux at the piston lip started to increase earlier, followed by the upper lip and lower lip resulting from the spray/wall interaction and mixture development. In addition, the heat flux at the chamber head showed the highest value and longest duration, which was primarily related to the initial location where the high-temperature flame appeared. Furthermore, combining the spray combustion images acquired from diffused backlight illumination (DBI) and the apparent heat release rate (AHRR) by analyzing the in-cylinder pressure, the results clarified the effect of high injection pressure on reducing the heat transfer and soot formation by improving the combustion performance.

A parametric study to improve first firing cycle emissions of a gasoline direct injection engine during cold start

A parametric study was carried out for the first firing cycle of a 4-cylinder, 2.0-liter, turbocharged gasoline direct injection (GDI) engine. The primary goal was to see how changes in the fuel injection parameters would affect the GDI engine combustion and emissions for the first four combustion events that constitute the first firing cycle. Experimental studies were carried out with a custom-designed powertrain control system to measure the HC emissions and pressure development for the first firing cycle. The quantitative experimental results were accompanied by simulations of the detailed temporal and spatial fuel concentration profiles using Converge CFD engine simulation software. An alternative calculation method was used to calculate the average combustion equivalence ratio for each of the four cylinders. This method showed that the majority of the cold start HC emissions during the first firing cycle was unburned gasoline and its possible decomposition products, which did not contribute significantly to the combustion and heat release. For the same amount of fuel injected into a cylinder, increased fuel rail pressure resulted in better evaporation and combustion, while slightly increasing the HC emissions during the cold start process. A multiple injection strategy was studied that split the fuel delivery between the intake stroke and the compression stroke with either one or two injections in each of those strokes (two or four injections total). The quadruple injection strategy led to better first cycle combustion, with higher engine IMEP and lower HC emissions. This resulted from a richer fuel mixture in the region near the spark plug due to better fuel evaporation and a better spatial fuel distribution. While increasing fuel rail pressure with either injection strategy failed to significantly lower the HC emissions given the same amount of injected fuel mass, higher rail pressure with the quadruple injection strategy resulted in higher IMEP for the same amount of injected fuel; this may provide the possibility to reduce the total fuel injection mass which may have benefits for both fuel consumption and emissions.

Utilization of renewable and sustainable diesel/methanol/n-butanol (DMB) blends for reducing the engine emissions in a diesel engine with different pre-injection strategies

In the face of the severe energy crisis and environmental crisis, actively finding and using alternative fuels rationally is one of the main ways to alleviate energy shortage and environmental pollution. Biomass fuels are alternative fuels with good development prospects. The addition of oxygenated biofuels can reduce the soot emission, but increase the nitrogen oxides (NOx) emission. Multiple injection strategies can be used to reduce the NOx emission. Therefore, this paper was mainly aimed at the parameters investigation of a medium-speed marine four-stroke diesel engine fueled with diesel/methanol/n-butanol (DMB) blended fuel. The effects of pre-injection (including pre-injection fuel timing (PT) and pre-injection fuel mass ratio (PMR)) on the engine combustion, performance, and emission parameters were obtained. In addition, an orthogonal test design was used to optimize the PT and PMR to determine the optimal combination. The simulation results showed that advancing PT and increasing PMR could increase cylinder pressure, which was increased by about 9.8%–14.57%. However, it decreased the cylinder temperature, and shorten ignition delay (ID) and combustion duration (CD). In addition, the use of the pre-injection strategies could reduce the emissions of the engine pollution, in which the emission of NOx was reduced by about 46.43%–87.18%, and the emission of hydrocarbons (HC) was reduced by about 24.05%–38.03%. However, the brake specific fuel consumption (BSFC) increased. The optimal combination parameters of PT and PMR obtained by orthogonal test design were −45 °CA and 0.3. At this point, the peak cylinder pressure was 8.83 MPa, the BSFC was 304.46 g/(kW·h), and the NOx emission was 168.74 ppm. Therefore, this study could provide some theoretical foundations for the optimization of fuel injection strategy coupled with the oxygenated fuels combustion process.

Numerical Investigation on the Combustion and Emission Characteristics of Diesel Engine with Flexible Fuel Injection

As the main engineering power plant, diesel engines are irreplaceable in the future. However, the stringent emission regulations impose many tough requirements to their developments. Recently, flexible fuel injection strategy has been recognized as an effective technology in creating an advanced spray and mixture formation and improving combustion efficiency indirectly. However, the detailed combustion and emission behaviors under flexible fuel injection are still unknown. Therefore, this paper aims to investigate the combustion and emission characteristics under flexible fuel injection and explore an optimal injection strategy for high-efficiency combustion. A numerical simulation method is conducted by coupling the large-eddy simulation (LES) model and the SAGE combustion model. Then, the spray mixing, combustion flame propagation and emissions formation under various multiple-injection strategies are investigated. Results reveal that initial an ultrahigh injection pressure has a significant influence on the spray’s axial penetration while dwell time mainly affects the spray’s radial expansion. Under an initial ultrahigh injection pressure, the turbulence kinetic energy (TKE) becomes larger, and the vortex motions are stronger, contributing to a better spray turbulent mixing. Meanwhile, a snatchier flame structure with a favorable level of equivalence ratio and a homogeneous temperature distribution is obtained. In this way, the peak heat release rate (HRR) could increase by 46.7% with a 16.7% reduction in soot formation and a 31.4% reduction in NOx formation.

EXPERIMENTAL AND NUMERICAL INVESTIGATION OF DUCTED SPRAY WITH DUAL INJECTION STRATEGIES

Ducted fuel injection (DFI) is a newly established technology showing great potential in breaking the soot/NOx trade-off. Multiple-injection strategy is also seen as a possible way to reduce soot and NOx emissions simultaneously. However, the applicability of these approaches is not fully understood. The present study investigated the spray characteristics of DFI technology coupled with a dual-injection strategy. Results showed that during the injection interval (the interval between two injections), ambient gas continues to flow into the duct due to the pressure difference between the duct inside and outside, which increases the velocity of the second injection. The spray penetration length development of ducted spray is faster than that of free spray in both the first and the second injection events. During the first injection, the distribution of the equivalence ratio of ducted spray is more uniform than free spray, and the peak value of the equivalence ratio of ducted spray is lower than that of free spray. Compared to the first injection, in the second injection, when the radial equivalence ratio distribution of ducted spray is equivalent to the that of free injection, the path of spray traversed is shorter. These indicate that DFI technology and dual injection strategy couples well in case of spray and mixing process.

Comprehensive investigation on ballistic injection characteristics of GDI injector: A particular focus on injection pressure and fuel effects

The ballistic injection occurs in the short injection pulse conditions of solenoid-actuated fuel injectors, in which the injection mass does not have a linear relationship with the coil energizing time (injection pulse duration). Sometimes, a reversal stage appears in the ballistic regime in which the injection mass temporarily decreases against the increase of injection pulse duration. Previous studies have observed these nonlinear injection characteristics but insufficient attention has been paid to what are the related mechanisms and how they appear differently based on injection parameters. Understanding these is of great importance for the advanced design and control of fuel injectors in conventional and alternative fuel engines, particularly applying the short-pulse multiple injection strategies. The current study investigates the injection pressure and fuel effects on ballistic and linear injection characteristics of a gasoline direct injection injector using a Bosch long-tube injection rate meter. In the long-pulse linear injection regime, the injection pressure effect showed a typical trend but the fuel effects appeared insignificant. However, these injection pressure and fuel effects appeared more complicated and dramatic in the ballistic regime. The increase in the injection pressure showed a slower needle rise which caused a shorter injection duration and the appearance of the reversal stage at a longer injection pulse duration. The higher fuel viscosity caused a longer injection delay, which resulted in a shorter injection duration, lower injection mass, and the appearance of the reversal stage at a longer injection pulse duration. The needle dynamics associated with the ballistic injection characteristics and their dependence on injection parameters were thoroughly discussed based on the results.

The multi-parameter optimization of injections on double-layer diesel engines based on genetic algorithm

In this paper, a coupling model of the NSGA-II genetic algorithm and KIVA-3 V program is developed to perform a multi-objective intelligent optimization study of the injection parameters in a diesel engine with double-layer diverging combustion (DLDC) chamber. Four optimization parameters, involving the first injection timing, the first fuel split ratio, the injection timing interval, and the exhaust gas recirculation (EGR) ratio, are optimized after comparing the pollutant emissions and fuel consumption characteristics. The computation results reveal that both soot and fuel consumption function as the optimization objectives, proving a trade-off relationship with the NOx emission. The analysis of the response surface demonstrates that the application of the multiple-injection strategies is beneficial for enhancing the performance of diesel engines. A large first fuel split ratio and a low EGR rate can minimize both ISFC (indicated specific fuel consumption) and soot emission concurrently. A high EGR rate can significantly reduce NOx emission. In addition, the distribution of the final Pareto font shows that 66.7 % percent of the first fuel split ratio is above 0.56, and only two solutions (8.3 %) have values below 0.35. Furthermore, three representative points of the first fuel split ratio are selected for combustion analysis, which are 0.05, 0.35, and 0.88. As the first fuel split ratio rises, the high-temperature areas in the cylinder are gradually enlarged, and the NOx emission is increased while the soot emission and ISFC are further reduced.

Effect of injection strategy optimization on PCCI combustion and emissions under engine speed extension in a heavy-duty diesel engine

To mitigate the consequent emissions of greenhouse gases and to conform to increasingly strict vehicle emission requirements, experiments and numerical simulation were used to study effects of multiple injection strategy on premixed charge compression ignition (PCCI) combustion and emissions under speed extension in a heavy-duty diesel engine fueled with diesel. As the speed increases, the injection duration is prolonged, the injection rate is decreased, the fuel-oxygen mixing degree is decreased. In order to enhance fuel-oxygen mixing, the injection timing of single injection should firstly be optimized to fully utilize the shape of the chamber. Compared with single injection, the double injections can increase the mixing time, the optimized multiple injections can further increase the mixing time, making the premixing more sufficient and the combustion more complete. Compared with double injections, the optimized multiple injection strategy used in this paper adds a short pulse pilot injection before the main injection, which prolongs the duration of turbulent motion in the cylinder, and enhances the mixing rate of the main injection fuel and air. Results reveals that for single injection with injection timing of −15°CA ATDC, at low speed, through optimizing the injection strategy, the NOx and soot emissions are reduced by 38.5% and one order of magnitude, respectively, and the gross indicated thermal efficiency (ITEg) is increased by 8.66%; at medium speed, by optimizing the injection strategy, the NOx and soot emissions are reduced by 59.3% and 70.4%, respectively, and the ITEg is increased slightly by 0.33%; at high speed, by optimizing the injection strategy, the soot emission is decreased significantly, the NOx emissions and the ITEg are increased slightly. It was found that with the increase of speed, the effect of multiple injection strategy on the ITEg and emissions is gradually increased, and the optimization effect of multiple injection strategy is more obvious than that of low speed.

Characterization of the Rate of Injection of Diesel Solenoid Injectors Operated in the Multiple Injection Strategy: A Comparison of the Spray Momentum and Bosch Tube Methods

Multiple injection strategies can be used for controlling the heat release rate in an engine, particularly in compression ignition engines. This can mitigate the heat transfer losses and overcome the limitation related to the maximum pressure allowed for a particular engine. Controlling heat release with repetitive injections requires precise characterization of the fuel injection rates. In such a configuration, the injector used should be characterized for its hydraulic delay, rate of injection, and the effect of dwell timing with multiple injections. This study investigates the fuel injection behavior of a high-flow-rate solenoid injector operated with single and double injections. Two characterization methods, the momentum flux, and the Bosch tube are used and compared to investigate their suitability with the multiple injection strategies. Experiments with single injection are conducted by varying the Energizing Timing (ET) from 0.5 up to 2 ms. The tests with multiple injections (i.e., double injections) are conducted with a fixed ET of 0.5 ms, while the dwell times (δt) are varied from 0.1 up to 1 ms. All tests are performed at 500, 1000, 1500, and 2000 bar rail pressures. Depending on the injection pressure, the injector’s needle could not fully close with short dwell times and the injections are merged. The momentum flux method has faster ramp-up and decaying and more oscillations in the quasi-steady-state phase compared to the Bosch tube method. The effective duration of injection is overpredicted with the Bosch tube method. The momentum flux method is demonstrated to be more suitable for measuring the ROI of multiple injection strategies.