Effect of exhaust gas recirculation and intake pre-heating on performance and emission characteristics of dual fuel engines at part loads

Achieving simultaneous reduction of NOx,CO and unburned hydrocarbon(UHC) emissions without compromising engine performance at part loads is the current focus of dual fuel engine research.The present work focuses on an experimental investigation conducted on a dual fuel(diesel-natural gas) engine to examine the simultaneous effect of inlet air pre-heating and exhaust gas recirculation(EGR) ratio on performance and emission characteristics at part loads.The use of EGR at high levels seems to be unable to improve the engine performance at part loads.However,it is shown that EGR combined with pre-heating of inlet air can slightly increase thermal efficiency,resulting in reduced levels of both unburned hydrocarbon and NOx emissions.CO and UHC emissions are reduced by 24% and 31%,respectively,The NOx emissions decrease by 21% because of the lower combustion temperature due to the much inert gas brought by EGR and decreased oxygen concentration in the cylinder.

Combustion and emission characteristics of diesel/n-butanol blends with split-injection and exhaust gas recirculation stratification

Oxygen fuels have broad application prospects and great potential for realizing efficient and clean combustion,and hence this study applies diesel/n-butanol blends to explore the influence of split-injection strategy on combustion and emission characteristics.Simultaneously,changing the way of exhaust gas recirculation(EGR)gas introduction forms uneven in-cylinder components distribution,and utilizing EGR stratification optimizes the combustion process and allows better emission results.The results show that the split-injection strategy can reduce the NO_(x)emissions and keep smoke opacity low compared with the single injection,but the rise in accumulation mode particles is noticeable.NO_(x)emissions show an upward trend as the injection interval expands,while soot emissions are significantly reduced.The increase in pre-injection proportion causes the apparent low-temperature heat release,and the two-stage heat release can be observed during the process of main combustion heat release.More pre-injection mass makes NO_(x)gradually increase,but smoke opacity reaches the lowest point at 15%pre-injection proportion.EGR stratification can optimize the emission results under the split injection strategy,especially the considerable suppression of accumulation mode particulate emissions.Above all,fuel stratification coupled with EGR stratification is beneficial for further realizing the in-cylinder purification of pollutants.

Collaborative optimization of exhaust gas recirculation and Miller cycle of two-stage turbocharged marine diesel engines based on particle swarm optimization

To meet increasingly stringent emission standards and lower the brake-specific fuel consumption(BSFC)of marine engines,a collaborative optimization study of exhaust gas recirculation(EGR)and a Miller cycle coupled turbocharging system was carried out.In this study,a one-dimensional numerical model of the EGR,Miller cycle,and adjustable two-stage turbocharged engine based on WeiChai 6170 marine diesel engine was established.The particle swarm optimization algorithm was used to achieve multi-input and multi-objective comprehensive optimization,and the effects of EGR-coupled Miller regulation and high-pressure turbine bypass regulation on NO_(x)and BSFC were investigated.The results showed that a medium EGR rate-coupled medium Miller degree was better for the comprehensive optimization of NO_(x)and BSFC.At medium EGR rate and low turbine bypass rates,NO_(x)and BSFC were relatively balanced and acceptable.Finally,an optimal steady-state control strategy under full loads was proposed.With an increase in loads,the optimized turbine bypass rate and Miller degree gradually increased.Compared with the EGRonly system,the optimal system of EGR and Miller cycle coupled turbine bypass reduced NO_(x)by 0.87 g/(kW·h)and BSFC by 17.19 g/(kW·h)at 100%load.Therefore,the EGR and Miller cycle coupled adjustable two-stage turbocharging achieves NO_(x)and BSFC optimization under full loads.

EFFECTS OF COOLED EXTERNAL EXHAUST GAS RECIRCULATION ON DIESEL HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE

The effects of cooled external exhaust gas recirculation （EGR） on the combustion and emission performance of diesel fuel homogeneous charge compression ignition （HCCI） are studied. Homogeneous mixture is formed by injecting fuel in-cylinder in the negative valve overlap （NVO） period. So, the HCCI combustion which has low NOx and smoke emission is achieved. Cooled external EGR can delay the start of combustion effectively, which is very useful for high cetane fuel （diesel） HCCI, because these fuels can easily self-ignition, which makes the start of combustion more early. External EGR can avoid the knock combustion of HCCI at high load which means that the EGR can expand the high load limit. HCCI maintains low smoke emission at various EGR rate and various load compared with conventional diesel engine because there is no fuel-rich area in cylinder.

Effects of Exhaust Gas Recirculation on the Homogeneous Charge Combustion Process of n-Heptane at Different Load Conditions

Effects of exhaust gas recirculation （EGR） on homogeneous charge combustion of n-heptane was studied through simulation and experiment. Experiments were carried out in a single cylinder, four-stroke, air cooled engine and a single cylinder, two-stroke, water cooled engine. In the four-stroke engine, experiments of the effects of EGR were examined using heated N2 addition as a surrogate for external EGR and modifying engine to increase internal EGR. The ignition timing was sensitive to EGR due to thermal and chemical effects. EGR or extra air is a key factor in eliminating knock during mid-load conditions. For higher load operation the only way to avoid knock is to control reaction timing through the use of spark ignition. Experimental and modeling results from the two-stroke engine show that auto-ignition can be avoided by increasing the engine speed. The two-stroke engine experiments indicate that high levels of internal EGR can enable spark ignition at lean conditions. At higher load conditions, increasing the engine speed is an effective method to control transition from homogeneous charge compression ignition （HCCI） operation to non-HCCI operation and successful spark ignition of a highly dilute mixture can avoid serious knock.

Analysis of Non-Selective Catalyst Reduction Performance with Dedicated Exhaust Gas Recirculation

Rich burn industrial natural gas engines offer best in class post catalyst emissions by using a non-selective catalyst reduction aftertreatment technology. However, they operate with reduced power density when compared to lean burn engines. Dedicated exhaust gas recirculation (EGR) offers a possible pathway for rich burn engines to use non-selective catalyst reduction aftertreatment technology without sacrificing power density. In order to achieve best in class post catalyst emissions, the precious metals and washcoat of a non-selective catalyst must be designed according to the expected exhaust composition of an engine. In this work, a rich burn industrial natural gas engine operating with dedicated EGR was paired with a commercially available non-selective catalyst. At rated brake mean effective pressure (BMEP) the air-fuel ratio was swept between rich and lean conditions to compare the catalyst reduction efficiency and post catalyst emissions of rich burn and dedicated EGR combustion. It was found that due to low oxides of nitrogen (NOx) emissions across the entire air-fuel ratio range, dedicated EGR offers a much larger range of air-fuel ratios where low regulated emissions can be met. Low engine out NOx also points towards a possibility of using an oxidation catalyst rather than a non-selective catalyst for dedicated EGR applications. The location of the NOx-CO tradeoff was shifted to more rich conditions using dedicated EGR.

Thermodynamic Performance Analysis of E/F/H-Class Gas Turbine Combined Cycle with Exhaust Gas Recirculation and Inlet/Variable Guide Vane Adjustment under Part-Load Conditions

Exhaust gas recirculation control(EGRC),an inlet air heating technology,can be utilized in combination with inlet/variable guide vane control(IGV/VGVC) and fuel flow control(FFC) to regulate the load,thereby effectively improving the part-load(i.e.,off-design) performance of the gas turbine combined cycle(GTCC).In this study,the E-,F-,and H-Class EGR-GTCC design and off-design system models were established and validated to perform a comparative analysis of the part-load performance under the EGR-IGV-FFC and conventional IGV-FFC strategies in the E/F/H-Class GTCC.Results show that EGR-IGV-FFC has considerable potential for the part-load performance enhancement and can show a higher combined cycle efficiency than IGV-FFC in the E-,F-,and H-Class GTCCs.However,the part-load performance improvement in the corresponding GTCC was weakened for the higher class of the gas turbine because of the narrower load range of EGR action and the deterioration of the gas turbine performance.Furthermore,EGR-IGV-FFC was inferior to IGV-FFC in improving the performance at loads below 50% for the H-Class GTCC.The results obtained in this paper could help guide the application of EGR-IGV-FFC to enhance the part-load performance of various classes of GTCC systems.

Combustion analysis of a hydrogen-diesel fuel operated DI diesel engine with exhaust gas recirculation

The rapid depletion of fossil fuel and growing demand necessitates researchers to find alternative fuels which are clean and sustainable. The need for finding renewable, low cost and environmentally friendly fuel resources can never be understated. An efficient method of generation and storage of hydrogen will enable automotive manufacturers to introduce hydrogen fuelled engine in the market. In this paper, a conventional DI diesel engine was modified to operate as gas engine. The intake manifold of the engine was supplied with hydrogen along with recirculated exhaust gas and air. The injection rates of hydrogen were maintained at three levels with 2 L/min, 4 L/min, 6 L/min and 8 L/min and 10 L/min with an injection pressure of 2 bar. Many of the combustion parameters like heat release rate （HRR）, ignition delay, combustion duration, rate of pressure rise （ROPR）, cumulative heat release rate （CHR）, and cyclic pressure fluctuations were measured. The HRR peak pressure decreased with the increase in EGR rate, while combustion duration increased with the EGR rate. The cyclic pressure variation also increased with the increase in EGR rate.

Influence of Exhaust Gas Recirculation on Low-Load Diesel Engine Performance

In the condition of constant speed and light load, an experimental study of a turbocharged and intercooled diesel engine with exhaust gas recirculation （EGR） system focuses on the influence of different EGR rates on combustion process, dynamic performance, economic performance and emission performance of a diesel engine. With the increase of EGR rate, the oxygen concentration of the intake-side decreases, the fuel air equivalence ratio increases, and the maximum explosion pressure in the cylinder decreases. Meanwhile, the average temperature in the cylinder drops, the ignition delay is prolonged, the ignition timing delays, and the maximum heat release rate decreases. The increase of EGR rate makes NOx emissions decrease obviously and continue to decline. When EGR is low, the smoke rate enlarges slowly with the increase of EGR rate, and enlarges greatly at the rate higher than 43% and reaches the maximum at the rate of 57%. When EGR rate is higher than 61%, the smoke rate drops rapidly, and the content of CO and hydrocarbon （HC） increases rapidly with high EGR rate.

Effect of exhaust gas recirculation and ethyl hexyl nitrate additive on biodiesel fuelled diesel engine for the reduction of NOx emissions

Cetane improvers reduce the ignition delay, which in turn reduces the combustion temperatures thereby reduce NOx emissions. Exhaust gas recirculation （EGR） proved to be an effective way to reduce the NOx emissions. In this present experimental work, a combination of exhaust gas recirculation and cetane improver ethyl hexyl nitrate （EHN） is used to investigate the performance and exhaust emissions of a single cylinder four stroke naturally aspirated direct injection and air cooled diesel engine. Test results show that the brake thermal efficiency increases with the increase in the percentage of EGR which is accompanied by a reduction in brake specific fuel consumption and exhaust gas temperatures, and that bio- diesel with cetane improver under 20% EGR reduces NOx emissions by 33% when compared to baseline fuel without EGR. However carbon monoxide （CO）, hydro carbon （HC） and smoke emissions increase with an increase in percentage of EGR.

Numerical simulation and optimization design of the EGR cooler in vehicle

The EGR (exhaust gas recirculation) technique can greatly reduce the NOx emission of diesel engines, especially when an EGR cooler is employed. Numerical simulations are applied to study the flow field and temperature distributions inside the EGR cooler. Three different models of EGR cooler are investigated, among which model A is a traditional one, and models B and C are improved by adding a helical baffle in the cooling area. In models B and C the entry directions of cooling water are different, which mostly influences the flow resistance. The results show that the improved structures not only lengthen the flow path of the cooling water, but also enhance the heat exchange rate between the cool and hot media. In conclusion we suggest that the improved structures are more powerful than the traditional one.

Simulation Research on the Effect of Cooled EGR, Supercharging and Compression Ratio on Downsized SI Engine Knock

Knock in spark-ignition（SI） engines severely limits engine performance and thermal efficiency. The researches on knock of downsized SI engine have mainly focused on structural design, performance optimization and advanced combustion modes, however there is little for simulation study on the effect of cooled exhaust gas recirculation（EGR） combined with downsizing technologies on SI engine performance. On the basis of mean pressure and oscillating pressure during combustion process, the effect of different levels of cooled EGR ratio, supercharging and compression ratio on engine dynamic and knock characteristic is researched with three- dimensional KIVA-3V program coupled with pressure wave equation. The cylinder pressure, combustion temperature, ignition delay timing, combustion duration, maximum mean pressure, and maximum oscillating pressure at different initial conditions are discussed and analyzed to investigate potential approaches to inhibiting engine knock while improving power output. The calculation results of the effect of just cooled EGR on knock characteristic show that appropriate levels of cooled EGR ratio can effectively suppress cylinder high-frequency pressure oscillations without obvious decrease in mean pressure. Analysis of the synergistic effect of cooled EGR, supercharging and compression ratio on knock characteristic indicates that under the condition of high supercharging and compression ratio, several times more cooled EGR ratio than that under the original condition is necessarily utilized to suppress knock occurrence effectively. The proposed method of synergistic effect of cooled EGR and downsizing technologies on knock characteristic, analyzed from the aspects of mean pressure and oscillating pressure, is an effective way to study downsized SI engine knock and provides knock inhibition approaches in practical engineering.

Numerical analysis of influence of expansion joints on welding residual stress of an EGR cooler

The influence of expansion joints on the welding residual stress at the tube-plate junction of an exhaust gas recirculation(EGR)cooler was studied by numerical simulation method.The simulation results show that the expansion joints set on the housing of the EGR cooler mainly for the sake of protecting the tube-plate joints from bearing additional heating stress can also reduce the welding residual tensile stress.The expansion joints set on the EGR cooler can mitigate the tensile force acting on the edges of the main plates through its elastic extension,and thus reduce the magnitude of welding residual tensile stress at the tube-plate junction.

Simulation of VGT control based on charge oxygen concentration

A turbocharged diesel engine model was built with the GT-Power software,and experimentally verified.Then two different control variables for the control of the variable geometry turbocharger（VGT）were described,and their distinct effects on engine performance,i.e.NOxand soot emissions and fuel consumption,were simulated and compared on the basis of this model.The results showed that NOxemissions decreased obviously with the increase of exhaust gas recirculation（EGR）rate at constant boost pressure condition,but soot emissions and fuel consumption considerably increased.It was a good way to reduce NOxemissions without increasing fuel consumption and soot emissions when VGT was controlled to maintain the excess oxygen ratio unchanged as EGR rate increases.

Nonlinear observer-based control design and experimental validation for gasoline engines with EGR

This paper presents a nonlinear observer-based control design approach for gasoline engines equipped with exhaust gas recirculation (EGR) system. A mean value engine model is designed for control which includes both the in take manifold and exhaust manifold dynamic focused on gas mass flows. Then, the nonlinear feedback controller based on the developed model is designed for the state tracking control, and the stability of the close loop system is guaranteed by a constructed Lyapunov function. Since the exhaust manifold pressure is usually unmeasurable in the production engines, a nonlinear observer-based feedback controller is proposed by using standard sensors equipped on the engine, and the asymptotic stability of the both observer dynamic system and control dynamic system are guaranteed with Lyapunov design assisted by the detail analysis of the model. The experimental validations show that the observer-based nonlinear feedback controller is able to regulate the in take pressure and exhaust pressure state to the desired values during both the steady-state and transient conditions quickly by only using the standard sensors.

Numerical study of effect of post injection coupled with EGR on combustion and emission performances of CRDI engine fueled with biodiesel-ethanol blends

Energy shortage and environmental pollution are becoming more serious,biodiesel is regarded as the most promising alternative fuel for diesel engines due to its environmentally friendly and renewable characteristics.In this study,the biodiesel-ethanol blends were used in a diesel engine,and the purpose of the study was to simultaneously control the NOx and soot emissions of the diesel engine by adjusting the injection strategy and EGR rate.A turbocharged,six-cylinder,common rail direct injection(CRDI)engine model was established using GT-Power.The effects of the main-post injection strategy and post injection coupled with exhaust gas recirculation(EGR)on combustion and emission characteristics were investigated at a maximum torque speed and a medium load.The results show that when the main-post injection strategy is employed,the combustion duration of the main injection is shortened with an increase in the main-post injection interval(MPI).When the MPI increased to more than 18℃A,the heat release of post injection could be observed clearly from the curve of the heat release rate,NOx emissions decreased by 5.70%and 7.12%,respectively,and soot emissions decreased by 25.56%and 30.20%,respectively.Moreover,with the increasing post injection quantity,the combustion duration of the main injection shortened,and the peak heat release rate(PHRR)of the post injection increased.When the fuel quantity for the post injection increased from 2 to 6 mg,NOx emissions decreased from 2.33%to 9.80%,and soot emissions decreased from 16.10%to 34.97%.The effect of post injection quantity on emissions was more significant than that of the MPI.In addition,with increasing EGR rate,the ignition delay is prolonged,the peak cylinder pressure,PHRR,peak combustion temperature and NOx emissions decrease,whereas soot emissions increase gradually.Main-post injection can improve the NO-soot trade-off,the optimal EGR rate is 22.86%under a post injection quantity of 4 mg and a MPI of 22℃A.

NOx Emission Reduction Technology for Marine Engine Based on Tier-Ⅲ:A Review

The development of maritime trade has greatly promoted the development of diesel engines.However,with the increasingly serious environmental problems,more and more attention has been paid to the exhaust emissions of high-power marine diesel engines.The restrictions on SOx have been implemented globally,and the limitation of the NO,will be the next priority.This paper illustrates(a)Principle and research progress of NOx emissions-reduction technology of marine diesel engine;(b)Summary of advantages and disadvantages among various reduction technologies and their reduction effects;(c)The application effect of mainstream technology on board.Firstly,since exhaust gas recirculation(EGR)can achieve Tier-Ⅲ directly from Tier-Ⅰ without considering the increased fuel consumption.It is deemed as the most promising technology to reduce emissions by controlling combustion condition.However,EGR has shortcomings of excessive increase in ftiel consumption and generation of waste water,which need to be solved immediately.Secondly,selective catalytic reduction(SCR)is the most effective and straightforward means to achieve Tier-Ⅲ.Despite of the continuous optimization of SCR unit volume,the problem of scrap catalyst seriously limits its wide application.How to match the supercharger more efficiently is a key factor in choosing between high and low pressure SCR.Thirdly,nature gas(NG)engines are capable of achieving a reduction in NOx,but in order to meet the requirements of Tier-Ⅲ,it still needs to be assisted by other technologies.The emissions of hydrocarbon(HC)and CO in NG engines are huge defects that must be solved.Lastly,technologies such as the Miller cycle,Two-stage supercharging and mixed-water combustion can also reduce emissions but were rarely used alone.These technologies can be combined with EGR,SCR and NG engines to optimize the enginesJ economy and emission characteristics.

Transient emission simulation and optimization o turbocharged diesel engine

In order to alleviate the pressure of experi- mental research of turbocharged diesel engine under transient operations, a whole process simulation platform for turbocharged diesel engine under transient operations was established based on the multi-software coupling technologies of Matlab/Simulink, GT-Power, STAR-CD and artificial neural network. Aimed at the contradiction of NOx and soot emission control with exhaust gas recirculation （EGR） of turbocharged diesel engine under transient operations, on this simulation platform, a transient EGR valve control strategy was proposed, which adjusted the EGR valve in adjacent level based on the feedback of its opening according soot control limit under transient operations. Simulation and experimental results prove that the transient emission optimization effect of this control strategy is obvious. On the one hand, compared with the previous control strategy, which closed the EGR valve during the whole transient operations, soot emission is slightly increased by 9.5%, but it is still 9% lower than the control limit. On the other hand, compared with the previous control strategy, NOx transient emission is reduced by 44%.

Experimental study on combustion pressure oscillation of soybean bio diesel oil

The principal objectives of this study were to examine in-cylinder combustion pressure oscillation characteristics of soybean biodiesel in time domain and time-frequency domain,and their influences on the control and operational parameters,such as injection timing,exhaust gas recirculation(EGR)ratio,engine load and engine speed.In this study,the combustion pressure oscillation characteristics of biodiesel engine for various injection timing,EGR ratio and engine speed were investigated.The corresponding relation of pressure characteristics in the time domain and frequency domain were obtained.The results showed that the pressure oscillation and peak pressure rise acceleration occurred mainly in the diffusion combustion,and the peak pressure rise rate located in the premixed combustion.The in-cylinder pressure level curve can be divided into three stages.The pressure levels of stage 1,stage 2 and stage 3 represent the peak in-cylinder pressure,the maximum amplitude of pressure rise rate and pressure rise acceleration,respectively.As the injection timing retards,the pressure levels of stage 1 and stage 3 decrease gradually.The pressure level curve of stage 3 with 25°before top dead center(BTDC)is the highest and the oscillation is the most significant.It is worth noting that the location of each stage with various operate conditions is not fixed.At 0.41 MPa indicated mean effective pressure(IMEP),with the increase of EGR rate,the pressure levels of stage 1 and stage 2 decrease gradually.The pressure level curve of stage 3 and the maximum amplitude of pressure rise acceleration with 0%EGR rate are the highest.The oscillation with 0%EGR rate is the most significant at 0.41 MPa IMEP.Compared to 0.41 MPa IMEP,the frequency bands of stage 1 and stage 2 at 1.1 MPa IMEP are relatively low due to the soft combustion in the cylinder.As EGR rate increases,the pressure level of stage 1 decreases,and those of stage 2 and stage 3 increase gradually.The oscillation with 30%EGR rate is the most significant.With the increase of engine speed,the pressure levels of stage 1 and stage 2 decrease,and move to the low frequency.The pressure level in the high frequency domain at 1600 r/min is less than that at 1100 r/min,and the combustion process is smooth.