Low-pressure Exhaust Gas Recirculation Research Articles

Conversion of a Small-Size Passenger Car to Hydrogen Fueling: 0D/1D Simulation of EGR and Related Flow Limitations

Hydrogen is seen as a prime choice for complete replacement of gasoline so as to achieve zero-emissions energy and mobility. Combining the use of this alternative fuel with a circular economy approach for giving new life to the existing fleet of passenger cars ensures further benefits in terms of cost competitiveness. Transforming spark ignition (SI) engines to H2 power requires relatively minor changes and limited added components. Within this framework, the conversion of a small-size passenger car to hydrogen fueling was evaluated based on 0D/1D simulation. One of the methods to improve efficiency is to apply exhaust gas recirculation (EGR), which also lowers NOx emissions. Therefore, the previous version of the quasi-dimensional model was modified to include EGR and its effects on combustion. A dedicated laminar flame speed model was implemented for the specific properties of hydrogen, and a purpose-built sub-routine was implemented to correctly model the effects of residual gas at the start of combustion. Simulations were performed in several operating points representative of urban and highway driving. One of the main conclusions was that high-pressure recirculation was severely limited by the minimum flow requirements of the compressor. Low-pressure EGR ensured wider applicability and significant improvement of efficiency, especially during partial-load operation specific to urban use. Another benefit of recirculation was that pressure rise rates were predicted to be more contained and closer to the values expected for gasoline fueling. This was possible due to the high tolerance of H2 to the presence of residual gas.

Physically-based control-oriented modeling for turbocharged stoichiometric spark-ignited engine with cooled EGR and flexible VVT systems

Accurate estimation and prediction of engine gas exchange system and in-cylinder conditions are critical for spark-ignited engine control and diagnostic algorithm development. In this paper, a physically-based, control-oriented model for a 2.8 l turbocharged, variable valve timing (VVT) and low pressure (LP) exhaust gas recirculation (EGR)-utilizing SI engine was developed. The model includes the impact of modulation to any combination of 10 actuators, including the throttle valve, compressor bypass valve, fueling rate, waste-gate, LP EGR valve, number of deactivated cylinders, intake valve open (IVO) timing, intake valve close (IVC) timing, exhaust valve open (EVO) timing and exhaust valve close (EVC) timing. The accuracy of the model in capturing engine dynamics was demonstrated by validating it against high-fidelity engine GT-Power simulation results for various drive cycles, particularly emphasizing elevated loads. In comparison to the open literature, novel contributions of the effort described in this paper includes in-cylinder gas composition modeling and turbine-out pressure estimation.

Influence of cooling loss on the energy and exergy distribution of heavy-duty diesel engines based on two-stage variable supercharging, VVT, and EGR

The application of mechanisms such as exhaust gas recirculation (EGR) coupled with variable valve timing (VVT) and a variable geometry turbocharger (VGT) can improve engine efficiency; however, the energy laws and loss distribution after EGR, VVT, and VGT changes are unclear, restricting the optimization of engine structures and corresponding strategies. Herein, a six-cylinder engine is studied, revealing that the cooling loss of the high-pressure (HP) EGR loop is an important factor affecting the engine energy distribution. The cooling loss accounts for 10.00%–20.00% of the total energy, with an average increase of 1.73%, surpassing other energy losses growth rates. The low-pressure (LP) EGR loop considerably reduces cooling losses. The cooling loss of the LP EGR loop is only 64.05% of the HP EGR loop at a 20% EGR rate. When the EGR rate is >10%, the resulting lower cooling losses effectively improve the engine efficiency and the indicated thermal efficiency (ITE) of the LP EGR loop is 0.20%–0.33% higher than that of the HP EGR loop; when the EGR rate is 21%, the ITE of the LP EGR loop reaches 49.52%. By studying the variation in exergy with operating parameters, it is found that while increasing the EGR rate from 15% to 20%, the proportion of available exergy increases by adjusting the VVT to −85° crank angle after top dead center (CA ATDC) or adjusting the VGT to 47.5% under the original operating scheme of the LP EGR loop (−146° CA ATDC; VGT = 42.5%). The available exergy increases from 71.22%–71.42% (−146° CA ATDC; VGT = 42.5%; original device) to 71.88%–71.58% (−146° CA ATDC; VGT = 47.5%) and 72.02%–72.21% (−85° CA ATDC; VGT = 42.5%). This study explores the energy distribution under different operating schemes, providing theoretical guidance for further improving the thermal efficiency of the entire device.

Prediction of Condensation in the Heat Exchangers of Engine Intake Systems according to External Environmental and Operating Conditions

Low-pressure exhaust gas recirculation (LP-EGR) systems are applied to diesel engines because they reduce nitrogen oxide emission by lowering the internal temperature of the cylinder by mixing the oxides with intake air. However, low-temperature ambient conditions include a large amount of vapor in the mixed gas flowing into the intercooler; when heat is exchanged, the water vapor condenses and is adsorbed on the surface of the intercooler fin to form a liquid film. Condensation occurs as the thermal resistance between the vapor and solid surface increases with the thickness of the liquid film and causing a corrosion due to condensation of the surface. In this study, the amount of condensation was predicted through calculations based on thermodynamic studies. Factors that can cause condensation inside the intercooler (fuel, air, and LP-EGR) were selected as variables. A mathematical formula was established to predict the convergence form of condensation or the amount of condensation over time at various temperature and relative humidity conditions. The formula predicted the condensation amount in the intercooler of the diesel engine, compared it to the actual amount of condensation in the test evaluation with an error of less than 4%. Additionally, because the formula can predict the amount of condensation by changing the heat exchange area of the intercooler, the application range of the formula was expanded to predict the condensation in the intercoolers of gasoline vehicles with different heat exchange areas and fuel types. The condensation error was within 2%, indicating a high consistency. Validation of the formula predicts a reliable amount of condensation under various operating and ambient temperature conditions, which means that both the time and cost of the test evaluation require the determination of the cause before solving the actual condensation problem.

Efficiency of limiting nitrogen oxides emissions by exhaust gas recirculation systems of marine internal combustion engines

The subject of this study is systems for ensuring environmental safety of marine internal combustion engines, in particular, technologies for limiting emissions of nitrogen oxides (NOx). The regulatory requirements for reducing emissions are presented in the paper. The main theoretical aspects of the problem of nitrogen oxides formation during combustion in a diesel engine are considered. On the basis of these theoretical aspects the effectiveness of using various methods to achieve the requirements for the permissible level of NOx concentration in the exhaust gases is assessed. Exhaust gas recirculation (EGR) systems and selective catalytic reduction (SCR) systems are considered as the main technologies; they allow achieving the highest indicators of nitrogen oxide emissions control in accordance with the requirements of the Tier 3 standard. Taking into account the peculiarities of the requirements for the design and layout of systems as part of a ship power plant, as well as operational and investment costs, the main attention in the work is paid to systems of indirect influence on the engine in-cylinder processes, which include exhaust gas recirculation systems. Based on the comparison of high and low pressure EGR, the advantages and disadvantages of the designs are determined. It is noted that high-pressure exhaust gas recirculation systems have a number of advantages, which primarily include the compactness and high speed of the system response to changes in operational conditions. On the example of the leading manufacturers developments, the potential capabilities of the high-pressure EGR system and the engine characteristics confirming the effectiveness of its use are demonstrated. Based on the results of the work, a conclusion about the high efficiency and expediency of using exhaust gas recirculation systems to meet the requirements of the current environmental safety standards of ship power plants is made.

Study on the Effect of Exhaust Gas Recirculation Coupled Variable Geometry Turbocharger and Fuel Quantity Control on Transient Performance of Turbocharged Diesel Engine

With increasingly stringent emissions regulations, there are growing demands for the transient performance of diesel engines. This study conducted a transient bench test on a two-stage turbocharged heavy-duty diesel engine to optimize its performance during a load increase (20% to 100% in 1 s) at a constant speed (1200 RPM) transient process. The results showed that the transient control scheme using the low-pressure EGR system resulted in a 42.1% reduction in the peak value of soot emission, a 24.8% decrease in the peak value of NOx emission, a 9.14% decrease in ISFC and a 30.6% increase in maximum IMEP achieved in 1 s, compared to the steady-state optimization control scheme without EGR. Transient control scheme using the high-pressure EGR system resulted in a 24.4% reduction in the peak value of soot emission, a 31.8% reduction in the peak value of NOx emission, a 9.52% reduction in ISFC, and a 31.7% increase in maximum IMEP achieved in 1 s. The comparison of high and low-pressure EGR systems revealed that the low-pressure EGR system produced lower compromising emissions, while alterations in control parameters for the diesel engine with a high-pressure EGR system had a more significant impact on the transient process performance.

Numerical investigations on the effects of EGR routes on the combustion characteristics and efficiency of a heavy-duty SI methanol engine

Exhaust gas recirculation (EGR) is one effective strategy to improve the thermal efficiency of the heavy-duty spark-ignition (SI) methanol engine. The high EGR tolerance of methanol engine raises new requirements for the EGR system. In this study, the influences of three different EGR routes, high-pressure EGR (HP-EGR), low-pressure EGR (LP-EGR), and high-low-pressure EGR (HLP-EGR) on the engine performance were studied by the one-dimensional simulation with the predictive combustion sub-model. The investigation was conducted at 1000 rpm and 1400 rpm, and 50% and 100% full load. Results show that EGR routes influence both the combustion characteristics and pumping mean effective pressure (PMEP), thus affecting the brake specific fuel consumption (BSFC). The EGR route with the lower internal EGR rate has a lower in-cylinder temperature at the compression stroke, a weaker knock tendency and a more advanced combustion phase. The effects of EGR routes on BSFC are more significant at the higher engine speed. The optimal BSFC of HP-EGR is lower than that of HLP-EGR and LP-EGR by up to 16.4 g/k·Wh and 21.2 g/k·Wh. Considering the engine performance at all engine operating conditions, HP-EGR is the optimal EGR route while LP-EGR is the worst one for the heavy-duty SI methanol engine.

Comprehensive Method for Obtaining Multi-Fidelity Surrogate Models for Design Space Approximation: Application to Multi-Dimensional Simulations of Condensation Due to Mixing Streams

In engineering problems, design space approximation using accurate computational models may require conducting a simulation for each explored working point, which is often not feasible in computational terms. For problems with numerous parameters and computationally demanding simulations, the possibility of resorting to multi-fidelity surrogates arises as a means to alleviate the effort by employing a reduced number of high-fidelity and expensive simulations and predicting a much cheaper low-fidelity model. A multi-fidelity approach for design space approximation is therefore proposed, requiring two different designs of experiments to assess the best combination of surrogate models and an intermediate meta-modeled variable. The strategy is applied to the prediction of condensation that occurs when two humid air streams are mixed in a three-way junction, which occurs when using low-pressure exhaust gas recirculation to reduce piston engine emissions. In this particular case, most of the assessed combinations of surrogate and intermediate variables provide a good agreement between observed and predicted values, resulting in the lowest normalized mean absolute error (3.4%) by constructing a polynomial response surface using a multi-fidelity additive scaling variable that calculates the difference between the low-fidelity and high-fidelity predictions of the condensation mass flow rate.

A CFD Modelling Approach for the Operation Analysis of an Exhaust Backpressure Valve Used in a Euro 6 Diesel Engine

Harvesting residual thermal energy from exhaust gases with thermoelectric generators is one of the paths that are currently being explored to achieve more sustainable and environmentally friendly means of transport. In some cases, thermoelectric generators are installed in a by-pass configuration to regulate the mass flow entering the thermoelectric generator. Some manufacturers are using throttle valves with electromechanical actuators and electronic control in the exhaust pipe to improve techniques for active control of pollutant emissions in reciprocating internal combustion engines, such as the exhaust gas recirculation. The above-mentioned circumstances have motivated the approach of this work: computational fluid dynamics (CFD) modelling of the operation of a throttle valve used for establishing adequate exhaust backpressure conditions to achieve the low pressure exhaust gas recirculation in Euro 6 engines. The aim of this model is to understand the flow control process with these types of valves in order to incorporate them in an exhaust system that will include two thermoelectric generators used to convert residual thermal energy into electrical energy. This work presents a computational model of the flow through the throttle valve under different temperatures and mass flow rates of the exhaust gas with different closing positions. For all cases, the values of the pressure drop were obtained. In all cases studied, the level of agreement between the modelled and experimental results exceeds 90%. The developed model has helped to propose a correlation to estimate the mass flow rate of exhaust gas from easily measurable quantities.

Effect of High and Low Pressure EGR on Diesel Engine Matched with Mechanical Turbo-compound

The mode of exhaust gas recirculation (EGR) and the flow of recirculated exhaust greatly impact the exhaust heat recovery of the mechanical turbo-compound. A matching mechanical turbo-compound of the diesel engine is established with GT-power software to study the effect of EGR mode and EGR rate on it, and the effect of EGR rate on the working performance of diesel engine and the mechanical turbo-compound under high-pressure EGR mode and low-pressure EGR mode is also studied. The results show that compared with the original engine, the effective thermal efficiency of the diesel engine matched with mechanical turbo-compound has been improved. Under the two EGR modes, as the EGR rate increase, the effective thermal efficiencies of diesel engine matched with mechanical turbo-compound and the original engine are decreasing. Under the maximum torque condition, the fuel economy of mechanical compound turbine diesel engine matched with low-pressure EGR system is better than with high-pressure EGR system; while underrated power condition, the fuel economy difference of mechanical compound turbine diesel engine matched with high-pressure EGR system and low-pressure EGR system is small.

Sensor selection and controller design method with application to turbocharged stoichiometric spark-ignited engine controls with low pressure EGR

This paper describes and demonstrates a model-based sensor selection and controller design framework for robust control of air–fuel-ratio, air flow and EGR flow for turbocharged stoichiometric engines using low pressure EGR, waste-gate turbo-charging, intake throttling and variable valve timing. Model uncertainties, disturbances, transport delays, and sensor- and actuator-characteristics are considered in this framework. Based on the required control performance and candidate sensor sets, the framework synthesizes an H∞ feedback controller and evaluates the viability of the candidate sensor set through analysis of the singular structured value μ of the closed-loop system in the frequency domain. The framework can also be used to understand if relaxing the controller performance requirements enable the use of a simpler (less costly) sensor set. The sensor selection and controller co-design approach is applied here, for the first time, to turbo-charged engines using exhaust gas circulation. High fidelity GT-Power simulations are used to validate the approach. The computed optimal controllers were able to maintain the AFR within 14.7 ± 0.3, control the torque within 8.2% error and the EGR ratio within 1.2% error at different drive cycles with sensor inaccuracies and actuator dynamics.

Nonlinear model predictive control of a DISI turbocharged engine with virtual engine co-simulation and real-time experimental validation

An increasing number of control actuators are being added to internal combustion engines to reduce fuel consumption and meet with emission standards. This research utilizes Nonlinear Model Predictive Control (NMPC) to manage a spark ignition engine equipped with a turbocharger, low pressure Exhaust Gas Recirculation (EGR), and Variable Valve Timing (VVT). This paper focuses on discussing the experimental setup and validation of the proposed NMPC strategy, while an overview of the control-oriented engine model and NMPC formulation is provided. The proposed NMPC-based engine control was implemented into a rapid prototype control system and successfully deployed during dynamometer tests. With a minimum amount of calibration effort, the NMPC exhibits sophisticated transient actuator control, which would otherwise require many calibration maps to achieve. A detailed discussion of these transient maneuvers is provided and reveals that these control actions indeed optimize the control objective function without violation of combustion and hardware capacity constraints.

Influence of the low-pressure exhaust gas recirculation injection point on engine performance

The use of low-pressure exhaust gas recirculation (EGR) has been extended in spark-ignited engines in recent years due to advantages from efficiency perspective. However, the potential condensation of the water contained in the exhaust gases and eventual compressor erosion can limit the usage of such systems during engine warm-up and/or cold ambient conditions. One possibility to avoid condensation at cold ambient is to place the EGR injection close to the compressor wheel, avoiding a complete mixture of both streams, but it alters the flow distribution upstream of the compressor, potentially affecting its performance. In order to assess the impact of this phenomenon in engine operation, a detailed experimental campaign in a state-of-the-art spark-ignition engine was performed comparing this close-coupled configuration with another one where the injection point was far upstream the compressor, ensuring a perfect mixing. A previously developed and validated one-dimensional model of the variable geometry turbocharger was used to analyze in further detail the compressor and turbine operation. The results show a general deterioration of the engine pumping mean effective pressure (up to 0.02 bar) and the specific fuel consumption (up to 4 g/kWh) when applying the close configuration, higher as the EGR rate increases, which is partially due to the change in turbine operation induced by the new compressor working point.

Energy recovery potential by replacing the exhaust gases recirculation valve with an additional turbocharger in a heavy-duty engine

A simulation-based assessment of different twin-turbocharging configurations allowing energy recovery from the exhaust gas recirculation flow is performed in a heavy-duty engine from the basis of a single-stage turbocharging architecture. This baseline configuration consists of a single stage turbocharged engine with a low-pressure exhaust gas recirculation system. Experimental data from the baseline engine tests are used to calibrate the model. The novelty of this study is to evaluate the energy recovery potential from the low-pressure exhaust gas recirculation flow by replacing its control valve with a turbine so that the flow energy is not lost due to the expansion across the valve. This additional turbine is coupled to a compressor placed in the intake line so that the turbocharging system is converted into a twin-turbocharging architecture. Different twin-turbocharging configurations are tested to attain maximum exhaust gas recirculation rates at 1100, 1500, and 2200 rpm engine speeds with boost pressures ranging from 1.8 to 2.6 bar. Fuel consumption calculations have been performed at constant exhaust gas recirculation rates for all three speeds as well as 1500 rpm partial load operation to attain 11.5 bar of brake mean effective pressure. The results in 8 engine running conditions show that twin-turbocharging with the compressors in series configuration with the exhaust gas recirculation turbine discharging after the first stage benefits, in average, from increasing about 5% maximum exhaust gas recirculation rates and saves up to 7% in fuel economy compared to the single-stage turbocharging layout.

Utilization of Hydrotreated Vegetable Oil (HVO) in a Euro 6 Dual-Loop EGR Diesel Engine: Behavior as a Drop-In Fuel and Potentialities along Calibration Parameter Sweeps

This study examines the effects on combustion, engine performance and exhaust pollutant emissions of a modern Euro 6, dual-loop EGR, compression ignition engine running on regular EN590-compliant diesel and hydrotreated vegetable oil (HVO). First, the potential of HVO as a “drop-in” fuel, i.e., without changes to the original, baseline diesel-oriented calibration, was highlighted and compared to regular diesel results. This showed how the use of HVO can reduce engine-out emissions of soot (by up to 67%), HC and CO (by up to 40%), while NOx levels remain relatively unchanged. Fuel consumption was also reduced, by about 3%, and slightly lower combustion noise levels were detected, too. HVO has a lower viscosity and a higher cetane number than diesel. Since these parameters have a significant impact on mixture formation and the subsequent combustion process, an engine pre-calibrated for regular diesel fuel could not fully exploit the potential of another sustainable fuel. Therefore, the effects of the most influential calibration parameters available on the tested engine platform, i.e., high-pressure and low-pressure EGR, fuel injection pressure, main injection timing, pilot quantity and dwell-time, were analyzed along single-parameter sweeps. The substantial reduction in engine-out soot, HC and CO levels brought about by HVO could give the possibility to implement additional measures to limit NOx emissions, combustion noise and/or fuel consumption compared to diesel. For example, higher proportion of LP EGR and/or smaller pilot quantity could be exploited with HVO, at low load, to reduce NOx emissions to a greater extent than diesel, without incurring penalties in terms of incomplete combustion species. Conversely, at higher load, delayed main injection timings and reduced rail pressure could reduce combustion noise without exceeding soot levels of the baseline diesel case.

On combustion instability induced by water condensation in a low-pressure exhaust gas recirculation system for spark-ignition engines

Water condensation in low-pressure exhaust gas recirculation systems is a concern because of a potential impact on components durability, but its implication into the operation of modern spark-ignition engines has not been investigated in detail. In this work, such aspects are evaluated by tests in a turbocharged multi-cylinder engine installed in a climatic test bench. First, a previously developed and validated zero-dimensional model is used to identify conditions where condensation is produced inside the water charge-air cooler, so that the compressor durability and operation is not affected. Then, different engine points are tested with a constant 25% of recirculated rate. Results show that combustion instability can increase up to 6% (absolute) due to droplets accumulation and release inside the water charge-air cooler, confirmed by an endoscope at the WCAC outlet . The evaporation of these droplets during the intake stroke causes charge overleaning in specific cycles, affecting combustion and inducing occasional misfires. Consequently, the fuel consumption and unburned hydrocarbons can be increased up to 4% and 30%, respectively, compared to the results achieved without condensation. The low speed and load condition was clearly the most affected by the sudden dilution given the lower in-cylinder temperatures. The combustion model shows that condensation formation and eventual overleaning phenomenon is increased if low or zero-carbon fuels such as natural gas, methanol, hydrogen or ammonia are used. Results showed an increased temperature for condensation compared to a traditional gasoline, around 10 ∘C for methane and methanol and 20 ∘C for hydrogen and ammonia.

Neural network-based air handling control for modern diesel engines

Complex air handling systems, featuring technologies such as exhaust gas recirculation (EGR) and variable geometry turbochargers (VGTs), are commonly used in modern diesel engines to meet stringent emissions and fuel economy requirements. The control of diesel air handling systems with EGR and VGTs is challenging because of their nonlinearity and coupled dynamics. In this paper, artificial neural networks (ANNs) and recurrent neural networks (RNNs) are applied to control the low pressure (LP) EGR valve position and VGT vane position simultaneously on a light-duty multi-cylinder diesel engine. Intake manifold pressure (IMP) and air-fuel equivalence ratio, or [Formula: see text], are selected as the control objectives since they directly impact engine emissions and cylinder power output. Meanwhile both signals are available on production engines, so no additional hardware costs for measurement systems will be introduced. Both transient and steady state experimental data are separately used to train the two categories of neural networks (NNs). The NNs with minimum mean square error (MSE) for the training data sets are compared to conventional proportional-integral (PI) control and model predictive control (MPC). The most accurate NN controller has almost no overshoot during the transient process while the steady state error [Formula: see text] and IMP are at most 7.0% and 3.8%, respectively, under a wide range of engine speeds from 2500 to 4000 rpm, thus showing the potential of this approach.

Compressor Surge Mitigation in Turbocharged Spark-Ignition Engines without an Anti-Surge Control System during Load-Decrease Operation

Automotive manufacturers are showing an increasing preference for hybrid powertrains based on advanced gasoline engines. The most extended solution to improve fuel economy in these engines consists in downsizing with direct injection, while turbocharging is required to compensate the consequent power loss. However, turbocharging is associated with different issues, such as compressor surge. It can appear during fast throttle closings (tip-outs), when the engine air flow is abruptly reduced. A usual strategy to manage this kind of maneuver is the installation of an anti-surge valve (ASV) that connects the compressor inlet and outlet when approaching the surge limit. In pursuit of cost reduction, the removal of the ASV system was assessed in this research. To this end, tip-outs without ASV were tested in a turbocharged gasoline engine equipped with a low-pressure EGR loop, and two strategies were analyzed: throttle closure optimization and reduction of the compressor inlet pressure through the intake flap (located upstream of the compressor to increase the EGR rate). The instantaneous compressor outlet pressure and its time derivative were used for surge detection. Experimental tip-outs without ASV revealed that applying a certain intake flap closing combined with an optimized throttle actuation led to a fast torque decrease, similar to that observed for the reference case with ASV, without compressor instabilities.

Numerical assessment of mixing of humid air streams in three-way junctions and impact on volume condensation

Flow mixing at three-way junctions is widely studied due to its usage in countless applications. Particularly, in air conditioning and internal combustion engines, the mixing of humid air streams can lead to volume condensation, provided that any local temperature achieves dew conditions. This work investigates and quantifies the correlation between mixing intensity and generated condensation. A method to define mixing indexes is developed, comparing its performance against literature references that employ temperature or passive scalar to evaluate mixing. A numerical campaign of 128 Reynolds-Averaged Navier Stokes three-dimensional (3D) simulations is designed to explore different junction operating conditions. A validated condensation submodel embedded in the 3D model enables the quantification of condensation at the junction outlet, which also can be estimated by means of a 0D model that provides the psychrometric state of a homogeneous mixture between the inlet streams. A strong linear correlation is found between condensation and the product of mixing indexes and 0D condensation mass flow rate, since the latter carries the psychrometric information of the working point. This connection allows to find junction design guidelines to reduce mixing and therefore condensation. Additional simulations confirm that removing junction valves, reducing mixing length, increasing the branch duct diameter and aligning the branch leg with the outlet duct significantly decrease condensation. In the framework of low pressure exhaust gas recirculation (EGR), this condensation damages the compressor wheel. If junctions are designed as suggested, the current constraints over EGR rates to limit condensation can be removed, which will result in internal combustion engines with lower emissions and better fuel consumption. • A new definition of mixing index is developed by calculating the unmixed area. • Flow mixing and condensation at T-junctions is assessed using 0D and 3D models. • Condensation is strongly correlated with psychometric conditions and mixing. • Mixing is reduced by decreasing length and momentum ratio and relocating valves. • Guidelines to design junctions with reduced volume condensation are provided.

Experimental study on ultra-low raw emissions in diesel/methanol dual fuel engine based on dual-loop EGR

In this paper, an experimental investigation on achieving ultra-low raw emissions in a diesel/methanol dual fuel engine based on dual-loop EGR was carried out. The effect of dual-loop EGR (High pressure EGR and low pressure EGR) on the combustion, performance and emissions of methanol engine has been studied comprehensively. The results show that ultra-low NOx (<0.4g/kWh) and PM (<10 mg/kWh) emissions can be achieved simultaneously in diesel methanol dual fuel engine with the help of EGR. The combustion phase is delayed with the increase of EGR rate in both EGR modes. However, the methanol equivalence ratio and in cylinder combustion temperature in high pressure EGR mode are significantly higher than those in low pressure EGR mode. Therefore, the CO and THC emissions are obviously lower in high pressure EGR mode than that in low pressure EGR mode. The combustion efficiency and brake thermal efficiency of the engine are 1.9% and 9.6% higher in high pressure EGR mode than those in low pressure EGR mode, respectively.