External Exhaust Gas Recirculation Research Articles

Parameter optimisation of marine four-stroke engine EGR systems using RSM and NSGA-III

ABSTRACT To reduce NOx emission of marine engines, an engine parameter optimisation method combining response surface method (RSM), Bayesian neural network and non-dominated sequence genetic algorithm (NSGA-III) is proposed. First, a simulation model of a marine four-stroke engine with an external exhaust gas recirculation (EGR) system was established and validated in AVL-BOOST software. Then, the five parameters of EGR valve opening, ignition advance angle, compression ratio (CR), intake valve opening (IVO) and exhaust valve closing (EVC) are selected as the decision parameters, and the three parameters of engine power, brake specific fuel consumption (BSFC) and NOx emission are taken as the target parameters to be optimised. In Design-Expert software, the response surface model is established by using the experimental design approach of central composite design (CCD), and the impact of decision parameters on target parameters are discussed by using response surface analysis. NSGA-III was used for the multi-objective optimisation of parameters, and the accuracy of NSGA-III was improved by the Bayesian neural network. The optimal solution is selected and verified by the technique for order of preference by similarity to the ideal solution (TOPSIS) approach. The results show that when the EGR valve opening is 47.5%, ignition advance angle is −18.99°CA, CR is 14.995, IVO is 15.27°CA and EVC is 7.68°CA, compared with the standard setting, the optimised power is increased by 4.17%, BSFC is reduced by 4.27%, and NOx emissions are reduced by 12.37%. Therefore, the combination of the Bayesian neural network and NSGA-III multi-objective optimisation can improve engine performance while reducing fuel consumption and NOx emissions.

Study on the Effect of Coupled Internal and External EGR on Homogeneous Charge Compression Ignition under High Pressure Rise Rate

This paper investigated the effects of exhaust gas recirculation (EGR) on homogeneous charge compression ignition (HCCI) combustion in internal combustion engines. The exhaust valve closing (EVC) timings were scanned to obtain a set of baseline operating points for HCCI, and the coupling control of the internal and external EGR was explored. The results indicate that external EGR delays HCCI ignition timing and slows down the combustion speed. As the internal EGR rate increases, the maximum external EGR ratio that can be tolerated decreases. For HCCI detonation operating points with low internal EGR rates, the addition of up to 10% of external EGR can control the pressure rise rate peak to less than 10 bar/°CA, resulting in reduced fuel consumption and increased indicated mean effective pressure (IMEP). However, for HCCI operating points with high internal EGR rates, the effect of external EGR is mainly observed in the control of the pressure rise rate, with limited increase in IMEP. Additionally, an increasing external EGR rate leads to a significant decrease in nitrogen oxide (NOx) emissions, while carbon monoxide (CO) and hydrocarbon (HC) emissions slightly increase before engine misfire occurs. These findings suggest that the coupling control of internal and external EGR should be explored further, particularly in relation to reducing the negative valve overlap (NVO) angle and improving combustion efficiency.

Performance and energy balance analysis of the downsized SI engine with using a novel OPCVCR and synchronized twin spark plugs configurations

Recently, the exhaust emissions become one of the main issues in the downsizing spark ignition (SI) engine. It is necessary to develop clean combustion and high efficiency SI engines for further increasing the performance and brake thermal efficiency. In this study, a novel opposite piston type continuous variable compression ratio (OPCVCR) mechanism combined with synchronous twin spark plugs configurations was proposed and applied in the turbocharged downsizing SI engine. The purpose of this study was to propose a novel type of OPCVCR engine and analyze its combustion, performance and energy balance characteristics. The results showed that the peak combustion temperature (PCT) and peak combustion pressure (PCP) of the OPCVCR engine with twin spark plugs were increased when the compression ratio (CR) increased. The knocking combustion intensity of the downsized SI engine was increased when the CR increased, while the knocking combustion intensity can be alleviated effectively by introducing the external EGR. In addition, the energy utilization efficiency was increased with increasing the CR of the OPCVCR engine with twin spark plugs. Besides, the indicated specific fuel consumption (ISFC) of the base downsized SI engine could be decreased by 23.59% and the indicated thermal efficiency (ITE) of the base downsized SI engine could be increased 21.62% by adopting CR 16 and introducing 10% external exhaust gas recirculation (EGR), respectively.

Optical diagnostic study of internal and external EGR combined with oxygenated fuels of n-butanol, PODE3 and DMC to optimize the combustion process of FT synthetic diesel

With the introduction of carbon neutrality target, Fischer-Tropsch (FT) synthetic fuels are coming back into the limelight as a kind of carbon–neutral fuel. However, the mismatch between the overly high cetane number (CN) and the relatively low vaporability of FT synthetic diesel is unfavorable to the soot emission control, which will make it difficult to meet more stringent fuel consumption and emission regulations in future applications. To investigate the potential of oxygenated fuels combined with different exhaust gas recirculation (EGR) introduction schemes to achieve high-efficiency and clean combustion of FT synthetic diesel, an optical diagnostic study was carried out based on high-speed photography and the two-color method. The results show that all three kinds of oxygenated fuels could suppress soot emissions via self-carrying oxygen and adjusting the physicochemical properties of the fuel blend. Compared with the combustion characteristics of FT synthetic diesel, the flame area and luminosity of oxygenated blends are reduced, and the in-cylinder temperature and soot KL factor are lowered. Among them, n-butanol exhibits a greater capability of soot control compared to polyoxymethylene dimethyl ethers (PODE3) and dimethyl carbonate (DMC). In addition, introducing internal and external EGR to the engine fueled by n-butanol/FT synthetic diesel blend shows that with the increase of EGR rate, the external EGR exhibits a gradually stronger inhibiting effect on the heat release process and soot KL factor, while the internal EGR exhibits an inhibiting and then promoting effect. Moreover, the high ratio internal EGR shortens the ignition delay (ID) significantly due to the strong heating effect, which is unfavorable to the control of soot emission. The combination of oxygenated fuels and internal/external EGR could effectively optimize the combustion process of FT synthetic diesel and inhibit soot generation, but the EGR rate needs to be controlled within a proper range.

Evaluation of energy-exergy performance and sustainability index of a DI engine integrated with designed electromechanical EGR cooling system

Exhaust Gas Recirculation (EGR) system is a commonly used pretreatment technique to improve pollutant emissions from modern diesel engines. Recently, the EGR cooling strategy focuses on improving combustion stability, NOx emission and fuel consumption values by controlling oxygen dilution, in-cylinder and exhaust gas temperatures. However, there are not enough studies focusing on energy and exergy analysis to improve the deterioration caused by hot EGR gas in engine performance and energy distributions. Therefore, in this study, classical and electronically controlled external EGR cooling systems are designed. The present study investigates the effect of the various EGR rates and EGRout gas temperatures on classical/electromechanics EGR cooling systems in a DI diesel engine and reveals the effects of energy-exergy distributions on each other and the sustainability index (SI) perspective. The tests are performed with various EGR rates (5%, 10%, 15%) and EGRout gas temperatures (75 °C, 90 °C, 110 °C) at 1700 and 2000 rpm. At 1700 rpm test conditions, the highest thermal-exergetic efficiencies for low and high load are recorded at 15% EGR rate-75 °C EGRout gas temperature and 5% EGR rate-75 °C EGRout gas temperature, respectively. At 2000 rpm test conditions, the highest thermal-exergetic efficiencies for low and high load are achieved at 15% EGR rate-110 °C EGRout gas temperature and 5% EGR rate-90 °C EGRout gas temperature, respectively. The main findings show that the EGR rate rather than the EGRout gas temperature has a more dominant effect on the in-cylinder combustion performance and thermal-exergetic efficiency. While the increase in the EGR rate from 5% to 15% contributes positively to the thermal-exergetic efficiency and SI performance at low engine load, the opposite is observed at high load. The study recommends that the EGR rate and EGRout gas temperature should be chosen at the optimum level for the engine performance and energy efficiency.

Development of Two-Step Exhaust Rebreathing for a Low-NOx Light-Duty Gasoline Compression Ignition Engine

The global automotive industry is undergoing a significant transition as battery electric vehicles enter the market and diesel sales decline. It is widely recognized that internal combustion engines (ICE) will be needed for transport for years to come; however, demands on ICE fuel efficiency, emissions, cost, and performance are extremely challenging. Gasoline compression ignition (GCI) is one approach for achieving the demanding efficiency and emissions targets. A key technology enabler for GCI is partially-premixed, compression ignition (PPCI) combustion, which involves two high-pressure, late fuel injections during the compression stroke. Both NOx and smoke emissions are greatly reduced relative to diesel, and this reduces the aftertreatment (AT) requirements significantly. For robust low-load and cold operation, a two-step valvetrain system is used for exhaust rebreathing (RB). Exhaust rebreathing involves the reinduction of hot exhaust gases into the cylinder during a second exhaust lift event during the intake stroke to help promote autoignition. The amount of exhaust rebreathing is controlled by exhaust backpressure, created by the vanes on the variable nozzle turbine (VNT) turbocharger. Because of the higher cycle temperatures during rebreathing, exhaust HC and CO may be significantly reduced, while combustion robustness and stability also improve. Importantly, exhaust rebreathing significantly increases exhaust temperatures in order to maintain active catalysis in the AT system for ultra-low tailpipe emissions. To achieve these benefits, it is important to optimize the rebreathe valve lift profile and develop an RB ON→OFF (mode switch) strategy that is easy to implement and control, without engine torque fluctuation. In this study, an engine model was developed using GT-Suite to conduct steady-state and transient engine simulations of the rebreathing process, followed by engine tests. The investigation was conducted in four parts. In part 1, various rebreathe lift profiles were simulated. The system performance was evaluated based on in-cylinder temperature, exhaust temperature, and pumping work. The results were compared with alternative variable valve actuation (VVA) strategies such as early exhaust valve closing (EEVC), negative valve overlap (NVO), positive valve overlap (PVO). In part 2, steady-state simulations were conducted to determine an appropriate engine load range for mode switching (exhaust rebreathing ON/OFF and vice-versa). The limits for both in-cylinder temperature and exhaust gas temperature, as well as the external exhaust gas recirculation (EGR) delivery potential were set as the criteria for load selection. In part 3, transient simulations were conducted to evaluate various mode switch strategies. For RB OFF, the cooled external EGR was utilized with the goal to maintain exhaust gas dilution during mode switches for low NOx emissions. The most promising mode-switch strategies produced negligible torque fluctuation during the mode switch. Finally, in part 4, engine tests were conducted, using the developed RB valve lift profile, at various low-load operating conditions. The mode switch experiments correlated well with the simulation results. The tests demonstrated the simplicity and robustness of the exhaust rebreathing approach. A robust engine response, low CNL, high exhaust gas temperature, and low engine out emissions were achieved in the low load region.

Impacts of using EGR and different DI-fuels on RCCI engine emissions, performance, and combustion characteristics

• EGR contributed to further reductions in NOx emissions in RCCI combustion. • Improvements in BTE and BSFC were achieved by using EGR in RCCI combustion. • Better RCCI operation with EGR requires an alternating premixed fraction. • Increased biodiesel dose in DI-Fuel lead to an increment in NOx emissions. Exhaust gas recirculation (EGR) seems to be a critical parameter in developed RCCI operations for controlling emissions, in-cylinder charge reactivity as well as combustion phasing. The most advantages of utilizing the RCCI burning technique are the simultaneous decrease of PM as well as NOx emissions. Nevertheless, significant challenges remain, such as extreme HC and CO emissions. The purpose of this work is to investigate the effects of external, hot, and high-pressure EGR as well as different DI-Fuels on RCCI combustion under various load conditions. The tests were performed on direct injection, single-cylinder, and four-stroke modified diesel engine (peak power 5 KW under 1500 rpm) operating in RCCI mode with an EGR system. To initiate ignition, high reactivity fuel (biodiesel/diesel blends) was injected directly inside the engine's cylinder whereas low reactivity fuel (LPG) was induced into to intake mixing chamber. EGR at various ratios (30%, 20%, and 10%) was introduced into the engine via the intake mixing chamber, and experiments were done under various loads. The results show that increasing EGR results in a slight increment in BTE under medium and high engine loads. NOx emissions from diesel engines operating in traditional RCCI mode declined dramatically, and they decreased even further with the addition of EGR. The CO and HC emission levels, on the other hand, are slightly greater when EGR is used. Increasing the proportion of biodiesel in DI-Fuel is resulting in a decrement in BTE and NOx emissions in addition to an increment in BSFC, CO, and HC emissions.

Experimental investigation and modelling of biodiesel combustion in engines with late direct injection strategy

The combination of alternate fuels, such as biodiesel, and low-temperature combustion (LTC) constitutes a promising solution to reduce pollutant emission and to avoid dependence on fossil fuels. However, this concept requires additional research to optimise LTC of biodiesel over wider operating ranges, specifically including the implementation of numerical models to assist in the development of these engines. In this work, an experimental analysis was carried out assessing both thermal performance and emissions derived from the LTC of diesel/biodiesel blends with late direct injection. Furthermore, this analysis allowed implementing a predictive tool to characterise in-cylinder pressure trace under this operation strategy. This model was coupled with an empirical law to simulate heat release during the combustion process. Least squares method was applied to fit this empirical law to experimental data involving different conditions in terms of percentages of rapeseed biodiesel in the fuel blend, rotational speed, fuel/air equivalence ratio and percentages of external exhaust gas recirculation. To build the predictive model, a multiple regression methodology was used to correlate the law parameters with the operating conditions. Finally, a validation process based on the simulation of in-cylinder pressure trace was developed, revealing that the predictions agreed well with the experimental data. This suggests that the proposed model is able to satisfactorily predict the LTC of diesel/biodiesel blends within the test range.

Spatially selective dilution - A novel approach for heat release control in continuous combustion

To support the ongoing energy transition and minimize the environmental footprint of combustion related technologies, the paper presents a novel approach for combustion control in gas turbines and burners. It relies on spatially targeted injection of inert components in the spray core where existent concepts fail to deliver the desired dilution rate and are unable to fully govern the spatial distribution of heat release rates. Combustion process control is thus possible by actively adjusting the composition and mass flow of spatially selective introduction of inert species in the spray, optionally combined with classic, external exhaust gas recirculation, leading to an ultimate fuel-flexible concept which is capable of adjustments to heterogeneous fuels, their reactivity and physical properties. The proof of concept is demonstrated in a gas turbine combustion chamber first by investigating the isolated effects of spatially selective injection of inert species, its comparison to external exhaust gas recirculation and a combination of both. The results confirm the superiority of the approach as spatially selective mixture inertization is capable of 7% reduction of NO emissions with merely 3% increase of CO emissions and even 9% reduction of PM emissions. Furthermore, the concept proved transferrable together with all its benefits to combustion cycles with external exhaust gas recirculation. In this case, the 63% reduction of NO emissions with no observed CO penalty is possible. Simultaneous exploitation of spatially selective inertization, as well as external exhaust gas recirculation forms a fully controllable concept - spatially selective dilution control (SSDC), which enables extensive adjustability of dilution rates throughout the spray core and primary zone of combustion chamber. Compared to baseline case, such approach was proved to simultaneously reduce CO, NO and PM emissions normalized to fuel thermal power for 39%, 63% and 91%, respectively. The confirmation of applicability of the novel approach and its potential to influence the local conditions is opening a series of possible uses, either as an original design feature for future fuel-flexible systems or as a retrofit approach in existent combustion systems.

Towards improved performance and lower exhaust emissions using exhaust gas recirculation coupled compression ignition engine fuelled with nanofuel blends

ABSTRACT Emission standards are becoming increasingly stringent. When it comes to diesel engine exhaust emissions, nitrogen oxides (NOx) and soot emissions need effective control as these emissions have a trade-off connection, making it difficult to achieve the emission regulation. To effectively manage NOx emissions from diesel engines, external exhaust gas recirculation has been implemented. The effects of EGR on the engine characteristics of a single-cylinder diesel engine running on pongamia methyl ester mixed with aluminum oxide nanoparticles are detailed in this work. The pongamia methyl ester was mixed with mineral diesel (25 vol. %). The nanofuel blend was made by mixing aluminum oxide nanoparticles with B25 fuel at a dosage of 100 ppm (B25A100). Experiments with diesel, B25, and B25A100 with various EGR rates were conducted in a compression ignition engine (10–30%). The combined impact of nanoparticles blended B25 with 20% EGR yielded a substantial reduction in NOx by 4.95% compared to B25. In addition, the unburnt hydrocarbon, carbon monoxide, and smoke emissions were found to increase as compared with B25. Arise in brake thermal efficiency of 4.6% was noticed for B25A100 + 20% EGR than that of B25. The brake specific fuel consumption was reduced by 4.23% for B25 blend. With 20% EGR, the in-cylinder pressure and instantaneous heat release rate were reduced. As a result, combining pongamia methyl ester with aluminum oxide nanoparticles and 20% EGR enhances engine performance while reducing emissions.

A Review of the External and Internal Residual Exhaust Gas in the Internal Combustion Engine

Efficiency and emission reduction are the primary targets of internal combustion engine research due the large number of vehicles in operation and the impact of emissions-related pollution on human and ecosystem health. Harmful components of engine exhaust gases include nitrous oxides (NOx), carbon dioxide, hydrocarbons, and particulate matter. NOx emissions in particular are associated with significant health threats. The recirculation of exhaust gases can reduce NOx emissions and improve engine efficiency when combined with other advanced techniques. On the other hand, the residual exhaust gas also effects on the quality of lubricating engine oil and therefore causes an increase in engine piston ring wear. In this review paper, the effects of external and internal exhaust gas recirculation on the performance and emission characteristics of diesel, gasoline, and alternative fuel engines are summarized and discussed in detail. Because it is difficult to estimate the internal residual exhaust gas in the combustion engine by doing experiments. This review paper introduces control strategies and prediction methods for internal and external exhaust gas recirculation.

Operation principles for hydrogen spark ignited direct injection engines for passenger car applications

The sustainable reduction of greenhouse gas emissions from road transport requires solutions to achieve net-zero carbon dioxide emissions. Therefore, in addition to vehicles with electrified powertrains, such as those implemented in battery electric of fuel cell vehicles, internal combustion engines fueled with e-fuels or biofuels are also under discussion. An e-fuel that has come into focus recently, is hydrogen due to its potential to achieve zero tank-to-wheel and well-to-wheel carbon dioxide emissions when the electrolysis is powered by electricity from renewable sources. Due to the high laminar burning velocity, hydrogen has the potential for engine operation with high cylinder charge dilution by e.g. external exhaust gas recirculation or enleanment, resulting in increased efficiency. On the other hand, the high burning velocity and high adiabatic flame temperatures pose a challenge for engine cooling due to increased heat losses compared to conventional fuels. To further evaluate the use of hydrogen for small passenger car engines, a series production 1 L 3 cylinder gasoline engine provided by Ford Werke GmbH was modified for hydrogen direct injection. The engine was equipped with a high pressure external exhaust gas recirculation system to investigate charge dilution at stoichiometric operation. Due to limitations of the turbocharging system, very lean operation, which can achieve nitrogen oxides raw emissions below 10 ppm, was limited to part load operation below BMEP = 8 bar. Thus, a reduction of the nitrogen oxides emission level at high loads compared to stoichiometric operation was not possible. At stoichiometric operation with external exhaust gas recirculation engine efficiency can be increased significantly. The comparison of stoichiometric hydrogen and gasoline operation shows a reduced indicated efficiency with hydrogen with significant faster combustion of hydrogen at comparable centers of combustion. However, higher boost pressures would allow to achieve even higher indicated efficiencies by charge dilution compared to gasoline engine operation.

Effect of the novel continuous variable compression ratio (CVCR) configuration coupled with spark assisted induced ignition (SAII) combustion mode on the performance behavior of the spark ignition engine

The paradox of low efficiency and high fuel consumption at low-load and high efficiency and knocking combustion at high-load are pushing the engine community to optimize compression ratio (CR) in the spark ignition (SI) engine. However, it is difficult to balance the performance under a wide load range with using a fixed CR. In this paper, a novel continuous variable compression ratio (CVCR) system was proposed and successfully used in a SI engine, which could continuously change the auxiliary combustion chamber volume, thereby achieving different compression ratios from 10.0:1 to 17.8:1. The results indicated that the total mass of residual exhaust gas in the cylinder of the engine equipped with CVCR system was increased, and the residual gas fraction (RGF) in the auxiliary cylinder was increased, while the RGF in the main cylinder wasn’t changed dramatically with increasing CR. In addition, combustion rate was increased and combustion duration was decreased with increasing CR. The heat transfer rate and its percentage in the total fuel energy was decreased with the increase of the CR. The BSFC and effective thermal efficiency of the engine equipped with CVCR system could be improved by 15.85% and 15.57% by adopting CR 17.8:1 and 10% external EGR under the operating condition of 2000 r/min and BMEP 9.59 bar, respectively. However, the intensity of knocking combustion was increased with CR and limited the utilization of the high CR in the SI engine. Using external exhaust gas recirculation strategy could greatly alleviate the knocking combustion and reduced the heat transfer rate through the combustion chamber wall, which was beneficial to increase the indicated thermal efficiency and adiabatic efficiency.

A comparative study of directly injected, spark ignition engine performance and emissions with natural gas, gasoline and charge dilution

This paper presents an experimental study of a 4-cylinder, downsized and boosted, spark ignition engine fuelled by either directly injected compressed natural gas (DI CNG) or gasoline (GDI). Three different charge preparation strategies are investigated for both fuels: stoichiometric engine operation without external dilution, stoichiometric operation with external exhaust gas recirculation (EGR) and lean burn.The performance of the optimized DI CNG engine is first shown to be comparable to that of the baseline GDI engine at stoichiometric conditions, exhibiting the potential of matching the peak torque at lower engine speeds with substantial fuel economy benefits. The impact of charge dilution on DI CNG engine performance is then examined with external EGR and lean burn. Between these two strategies, lean burn demonstrates higher brake thermal efficiency than that of stoichiometric operation with external EGR at equivalent dilution levels. Similar tests are performed with GDI fuelling and the results are compared to those of DI CNG, showing that a charge dilution strategy’s influence on engine performance is fuel specific. The engine-out total CO2 equivalent emissions of a DI CNG engine utilizing all three modes of operation are then assessed and compared to those of stoichiometric GDI operation over a range of engine operating conditions. DI CNG operation consistently demonstrates lower total CO2 equivalent emissions than GDI, though the final choice of DI CNG combustion strategy requires consideration of the aftertreatment system.

The Synergies of Valve Overlap Reduction and External Exhaust Gas Recirculation Dilution at Boosted Loads of a Downsized Gasoline Turbo Direct Injection Engine

The Synergies of Valve Overlap Reduction and External Exhaust Gas Recirculation Dilution at Boosted Loads of a Downsized Gasoline Turbo Direct Injection Engine

Nonlinear feedforward controller design for air-path system with transport dynamics of external EGR system

Abstract Advanced combustion, such as homogenous charge compression ignition (HCCI), requires precise control of the in-cylinder gas condition. Such advanced combustion does not always result in stoichiometric combustion; therefore, the changes in the oxygen concentration of the burned gas must be considered in the controller design. Furthermore, the changes in the oxygen concentration in the exhaust manifold are transferred to the intake manifold with delay. In this research, the transport dynamics of the exhaust gas recirculation (EGR) path were modeled by a pure time-varying delay and a second-order filter, and the model was used to estimate the oxygen concentration through the EGR valve. The feedforward controller was obtained based on the inverse model, which calculates the throttle and EGR valve positions based on the target values of the intake manifold pressure, EGR ratio, and estimated oxygen concentration at the EGR valve. The control performance of the proposed feedforward controller was evaluated by conducting simulations using both the mean value model and the precise model constructed using 1D simulation software.

Impact of Exhaust Gas Recirculation on Gaseous Emissions of Turbocharged Spark-Ignition Engines

Exhaust gas recirculation is one of the technologies that can be used to improve the efficiency of spark-ignition engines. However, apart from fuel consumption reduction, this technology has a significant impact on exhaust gaseous emissions, inducing a significant reduction in nitrogen oxides and an increase in unburned hydrocarbons and carbon monoxide, which can affect operation of the aftertreatment system. In order to evaluate these effects, data extracted from design of experiments done on a multi-cylinder 1.3 L turbocharged spark-ignition engine with variable valve timing and low-pressure exhaust gas recirculation (EGR) are used. The test campaign covers the area of interest for the engine to be used in new-generation hybrid electric platforms. In general, external EGR provides an approximately linear decrease of nitrogen oxides and deterioration of unburned hydrocarbon emissions due to thermal and flame quenching effects. At low load, the impact on emissions is directly linked to actuation of the variable valve timing system due to the interaction of EGR with internal residuals. For the same external EGR rate, running with high valve overlap increases the amount of internal residuals trapped inside the cylinder, slowing down combustion and increasing Unburnt hydrocarbon (HC) emissions. However, low valve overlap (i.e., low internal residuals) operation implies a decrease in oxygen concentration in the exhaust line for the same air–fuel ratio inside the cylinders. At high load, interaction with the variable valve timing system is reduced, and general trends of HC increase and of oxygen and carbon monoxide decrease appear as EGR is introduced. Finally, a simple stoichiometric model evaluates the potential performance of a catalyst targeted for EGR operation. The results highlight that the decrease of nitrogen oxides and oxygen availability together with the increase of unburned hydrocarbons results in a huge reduction of the margin in oxygen availability to achieve a complete oxidation from a theoretical perspective. This implies the need to rely on the oxygen storage capability of the catalyst or the possibility to control at slightly lean conditions, taking advantage of the nitrogen oxide reduction at engine-out with EGR.

Experimental study of effects of exhaust gas recirculation on combustion, performance, and emissions of DME-biodiesel fueled engine

The effects of exhaust gas recirculation (EGR) on the combustion, performance, and emissions of a six-cylinder turbocharged common-rail dimethyl ether engine with biodiesel blends were experimentally investigated. The proportions of biodiesel were 0% (B0), 5% (B5), 10% (B10), 15% (B15) and 20% (B20) by weight, and the effect of the engine load was considered. The results indicate that a higher EGR rate increases the ignition delay and combustion duration. The peak rate of heat release increases as the EGR rate increases at low loads but decreases at high loads. The present investigation shows that the EGR strategy is effective for suppressing NOx formation and the NOx emissions approximately linearly decrease as the EGR rate increases. The retardation of the combustion phase by external EGR effectively reduces the rate of pressure increase. The effect of the biodiesel proportion on the combustion and performance of an engine is complex, and the B5 blend showed the shortest ignition delay and the highest brake thermal efficiency. The influence of the biodiesel proportion on the EGR is not obvious. The disadvantages of EGR and biodiesel addition include the resultant increases in the CO and HC emissions and the particle number concentration.

Autoignition behavior of a full boiling-range gasoline: Observations in RCM and GCI engine environments

The understanding of, and capability to modulate fuel autoignition behavior are important aspects towards the development of advanced, low temperature combustion (LTC) engine concepts, which have potential to significantly increase engine efficiency while at the same time addressing emissions concerns. Proper combustion phasing and control of heat release rates via, for instance, multiple injections and exhaust gas recirculation, are significant challenges that can vary with fuel composition. Overall reactivity, which is a strong function of the in-cylinder temperature and pressure, is a prime driver for regulating combustion timing, while preliminary exothermicity, in the form of low- and intermediate-temperature heat release (LTHR, ITHR) can inhibit, or facilitate operational success, e.g., control combustion phasing. There are still gaps in understanding these features and how they interact with needs of advanced combustion engines, and how practical fuels can be rated for the new challenges of LTC engines.This work utilizes a rapid compression machine (RCM) and gasoline compression ignition (GCI) engine to probe the autoignition behavior of a California Reformulated Gasoline Blendstock for Oxygenate Blending (CARBOB) (RON = 86, MON = 81.4) under quasi- homogeneous charge compression ignition (qHCCI) operation. A wide range of thermodynamic conditions is explored (Tc = 700–1000 K, Pc = 15–90 bar) where ignition delay times and LTHR/ITHR are quantified. Both stoichiometric, dilute (11% O2) and lean (equivalence ratio (ϕ) = 0.23) fuel loading conditions are considered. The GCI engine is operated under fuel-lean conditions (ϕ = 0.23) using no external exhaust gas recirculation over a range of intake temperature (Tin = 30–70 °C), with the intake pressure adjusted (Pin = 1.2–1.3 bar) to achieve constant combustion phasing (CA50 = −4 °aTDC). Preliminary exothermicity is also quantified under these conditions.The stoichiometric, dilute RCM measurements reveal negative temperature coefficient (NTC) behavior for this fuel and indicate that rates and extents of LTHR and ITHR are both affected by the compressed conditions, with temperature imposing an inverse dependence, while increased pressure causes LTHR to increases, but ITHR to decrease. These are the first experimental quantifications of ITHR trends for a practical fuel under well-controlled, static conditions. When the lean RCM measurements are mapped to the in-cylinder conditions of the engine, it is found that under a constant combustion phasing scenario (as used in the engine), the fuel has little overall temperature sensitivity, while the starts of high temperature heat release (soHTHR) and top dead center (TDC) points seen along the engine compression trajectories correspond to isopleths of ignition delay times τRCM = 6 and 3 ms, respectively. In addition, the points of peak LTHR rate in the engine correspond to an isopleth of first-stage ignition τ1,RCM = 0.50–0.75 ms. Correlating the magnitudes of LTHR and ITHR measured in the RCM to the engine requires quantification of the preliminary exothermicity at the thermodynamic conditions of peat LTHR rate and soHTHR, respectively. The current measurements demonstrate how fundamental data from an RCM can be used to project expected trends in overall fuel reactivity to a qHCCI engine environment, and thus provide a possible avenue for characterizing fuels for LTC engines.

Strategy of improving fuel consumption and reducing emission at low load in a diesel methanol dual fuel engine

The experiments were performed to achieve a significant reduction in nitrogen oxides (NOx) and soot emissions while achieving no reduction in Brake Thermal Efficiency (BTE) for Diesel Methanol Dual Fuel (DMDF) engine at low load condition. The optimization strategies mainly include internal exhaust gas recirculation (EGR), external EGR, intake air heating and diesel injection timing retarded. NOx and soot emissions, BTE, and combustion characteristics were discussed. Experiments were conducted at 1660 r/min with the output torque 220 N·m, corresponding to 50% of full engine load. The main parameters for evaluating the optimization results include NOx emissions, soot emissions, BTE, Pressure Rising Rate (PRR) and fuel cost. The optimized result of DMDF mode is obviously better than those of diesel mode. The optimization process for DMDF mode weakens the trade-off relationship between key parameters which includes NOx emissions, soot emissions, BTE, PRR and fuel cost. Meanwhile, NOx emissions are significantly lower than those from the baseline diesel mode, which decreases from 9.76 to 1.53 g/kW.h. Soot emissions are almost maintained at the level of the baseline diesel mode. The optimized fuel cost of DMDF mode is greatly improved, and the BTE is slightly higher than that of baseline diesel mode.