Low-pressure Exhaust Gas Recirculation Research Articles

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.

Study on methanol premixed coupled with EGR to achieve ultra-low emissions in diesel engine

In this paper, an experimental investigation on achieving ultra-low emissions in diesel engine was carried out using intake premixed methanol and EGR technology. The influence of EGR introduction method on combustion and performances were studied comprehensively. The results show that ultra-low NOx (<0.4g/kWh) and PM (<10mg/kWh) emissions can be achieved simultaneously in diesel methanol dual fuel (DMDF) highly premixed low-temperature combustion mode. Compared with low-pressure EGR (LP-EGR), the excess air coefficients under high-pressure EGR (HP-EGR) drops more significantly. At the same EGR rate, the in-cylinder mean temperature and equivalent of mixture are higher under HP-EGR conditions, which results in higher combustion efficiency, lower CO and THC emissions. The maximum brake thermal efficiency of high-pressure EGR is 9.6% higher than that of low-pressure EGR.

Effect of LP-EGR on the Emission Characteristics of GDI Engine

Exhaust gas recirculation (EGR) can improve the fuel economy of gasoline direct-injection (GDI) engines, but at the same time it will have a significant impact on emissions. In this paper, the effects of low-pressure exhaust gas recirculation (LP-EGR) and its rate on the main gaseous and particulate emission characteristic of a GDI engine were investigated. The results showed that the particle size distribution of the GDI engine presented bimodal peaks in nucleation and accumulation mode, and the nucleation mode particles comprised the vast majority of the total particles. The effect of LP-EGR on emissions depended on the engine conditions. At low and medium speed, the particle emissions increased with the increase in the EGR rate, while at high speed, a reduction in the particle emission was observed. When the engine operated in full load condition, an increase in the EGR rate reduced the particle number (PN) concentration significantly, but increased the particle mass (PM) concentration. In terms of the gaseous emission, the EGR could reduce as much as 80% of the NOx emission; however, the total hydrocarbons (THC) emission presented an increased trend, and the maximum increase reached 23.5%. At low and medium loads, the EGR could reduce the CO emission, but at high load, the CO emission worsened with the EGR.

Assessment of air-management strategies to improve the transient performance of a gasoline engine under high EGR conditions during load-decrease operation

Advanced gasoline engines in hybrid powertrains are currently regarded as the most widespread solution for passenger cars in the upcoming years, due to the strong commitment of many countries to reduce greenhouse gas emissions and the limitations of pure electric vehicles at present. At the same time, it is widely proven that exhaust gas recirculation (EGR) through the low pressure (LP) configuration allows reducing fuel consumption and, consequently, CO2 emissions in gasoline engines. However, it is challenging to extract the full EGR potential, since it means operating close to the EGR tolerance, and this can compromise the engine transient response because of the long transport delays associated with LP EGR systems. Hence the paper presents an analysis on the capability of three strategies to accelerate the transient response of a gasoline engine operating with high LP EGR levels during tip-out maneuvers, while guaranteeing the combustion stability. Such strategies are the optimization of valve synchronization (based on applying different delays between the throttle actuation and pedal demand), the integration of a secondary air-path which bypasses the compressor, and the use of a pressurized air tank directly connected to the intake manifold. Both experimental and modeling data were utilized to assess the advantages and drawbacks of these strategies: engine tests for the validation of 1D model transient performance and the evaluation of combustion stability and torque evolution, while the fluid-dynamics and transport phenomena were analyzed by simulation.

Quantitative validation of an in-flow water condensation model for 3D-CFD simulations of three-way junctions using indirect condensation measurements

The usage of three way junctions to merge fluid streams is widely extended. For certain applications, such as refrigeration systems or internal combustion engines, the mixing of humid gaseous flow leads to bulk condensation, which compromises the integrity of the downstream elements. In this work, a test bench is adapted to manage the mixing of wet streams and a novel experimental technique is developed to measure condensation indirectly. Well-resolved temperature distributions are measured by means of a rotating array of thermocouples at experiments with and without humidity. Enthalpy balances using temperature distributions of both cases allow to infer the condensation mass fraction field. 3D CFD simulations with an in-flow condensation sub-model are compared with these measurements for two junction geometries and two operating conditions, with an average agreement of 11% in terms of condensation mass flow rate. The three-way junction design and its ability to reduce mixing is found to be of paramount importance to reduce bulk condensation. This validated model is therefore suitable for optimizing the junction geometry in terms of condensation reduction. With limited water condensation, NOx, CO2 and particulate matter emissions can be strongly abated for internal combustion engines by extending the usage of low-pressure exhaust gas recirculation to cold conditions.

Calculation studies of the influence of exhaust gas recirculation on the characteristics of the natural gas-fueled diesel engine

When converting diesel engines to run on natural gas on the gas-diesel cycle, additional problems arise associated with the high thermal stress of the exhaust valves and valve seats at high loads and engine speeds. There is also an increase in NOx emissions due to higher combustion temperatures of natural gas. One of the ways to improve the economic and environmental performance of engines operating on a gas-diesel cycle with a lean air-fuel mixture is to optimize the combustion of the air-fuel mixture by using an exhaust gas recirculation system (EGR). The principle of operation of this system is as follows: exhaust gas entering the intake manifold and further into the combustion chamber reduces the oxygen concentration in the air-fuel mixture, which leads to a dilution effect and, accordingly, to a decrease in combustion temperature and a decrease in NOx content. In order to study the influence of EGR on the dual-fuel gas and diesel engine parameters in the AVL Boost software package, a computer model of the existing 6ChN13/15 engine was developed. A low-pressure EGR system with an exhaust gas cooler was simulated on this engine. Values of NOx emissions, brake specific fuel consumption (BSFC) and brake efficiency have been obtained at different recirculation rate by calculation method. These values allow to estimate the feasibility of using a cooled EGR in a natural gas-fueled diesel engine.

Fuel consumption and aftertreatment thermal management synergy in compression ignition engines at variable altitude and ambient temperature

New regulations applied to the transportation sector are widening the operation range where the pollutant emissions are evaluated. Besides ambient temperature, the driving altitude is also considered to reduce the gap between regulated and real-life emissions. The altitude effect on the engine performance is usually overcome by acting on the turbocharger control. The traditional strategy assumes to keep (or even to increase) the boost pressure, that is, compressor pressure ratio increase, as the altitude is increased to offset the ambient density reduction, followed by the reduction of the exhaust gas recirculation to reach the targeted engine torque. However, this is done at the expense of an increase on fuel consumption and emissions. This work remarks experimentally the importance of a detailed understanding of the effects of the boost pressure and low-pressure exhaust gas recirculation (LP-EGR) settings when the engine runs low partial loads at different altitudes, accounting for extreme warm and cold ambient temperatures. The experimental results allow defining and justifying clear guidelines for an optimal engine calibration. Opposite to traditional strategies, a proper calibration of the boost pressure and LP-EGR enables reductions in specific fuel consumption along with the gas temperature increase at the exhaust aftertreatment system.

Analysis of condensation and secondary flows at three-way junctions using optical visualization techniques and computational fluid dynamics

Three-way junctions are employed in almost all piping systems, whenever two streams need to be merged into one duct. In some applications, the mixing between streams plays an important role for determining the performance of downstream elements. The situation is particularly interesting for low pressure Exhaust Gas Recirculation (EGR) junctions featured in piston engines, where warm humid exhaust gases meet cold fresh air, since the mixing of both streams can produce water condensation. This condensation deteriorates the integrity and performance of the adjacent compressor wheel. This work explores the aforementioned flow configuration in a three-way junction by means of a novel gas test bench that allows the characterization of the transversal section at the junction outlet, and 3D Computer Fluid Dynamics (CFD) simulations embedded with a previously-developed condensation model. Two optical techniques are employed: laser particle image velocimetry, which is used to characterize the cross-section secondary flows, and planar laser-induced visualization, which is employed for the first time to obtain the condensation pattern. The experimental measurements are conducted at two different working points and for two different three-way junction designs, being in agreement with 3D CFD simulations. Particularly, the overall luminosity captured in the experiments presents the same trends than the numerical condensed mass fraction. This innovative validation proves that a CFD model employing a psychrometric-based condensation submodel can be used as a tool to quantify the condensation produced in a three-way junction. The proposed tools are shown to be helpful for the development of advanced LP-EGR systems to reduce NOX,CO2 and particulate matter emissions during engine warm-ups.

Effect of EGR strategy on combustion and emission of DMDF engine for meeting China VI emission legislation

Study on EGR mode and demand were carried out to meet with the requirements of main emission limits of China VI on a diesel methanol dual fuel (DMDF) engine equipped with Hybrid exhaust gas recirculation (EGR) system coupled with back pressure valve (BPV). According to the World Harmonized Steady-State Cycle (WHSC) test cycle, the effects of EGR mode under high methanol energy ratio (MER) on the combustion, emissions and economy of DMDF engines were studied without the help of selected catalyst reduction (SCR). Considering the weight based on WHSC test cycle of full load was only 0.083, and EGR demand of full load was low, the optimal EGR strategy under different loads except full load was determined for DMDF engine. The results demonstrated that through the early injection strategy with high MER, particulate matter (PM) emissions were all at an extremely low level, far below the requirements by legislation limit of 0.01 g/kWh. With the increase of EGR rate, nitrogen oxides (NOx) emissions were significantly reduced under different loads, accompanying with one or more EGR modes at 25%, 50%, and 70% loads to ensure that NOx emission could meet the requirements by legislation limit of 0.4 g/kWh, while PM emissions were at a very low level at the same time. Demand for EGR rate of light loads was generally higher than that for medium loads, but under light loads, each of hybrid EGR modes could meet the demand of China VI legislation. While under medium loads, the dual loop (DL) EGR modes, i.e., both low pressure (LP) and high pressure (HP) EGR mode must be needed. In LP EGR mode combined with back pressure valve (BPV), higher EGR rate was required under the same NOx control target, owing to the higher intake air volume than those of other modes. The trade-off relationship in HP_BPV mode between NOx and PM emissions still existed, and high EGR rate often leaded to an increase in PM.

Tailored Air-Handling System Development for Gasoline Compression Ignition in a Heavy-Duty Diesel Engine

The simultaneous application of new low-NOx emissions standards and greenhouse gas (GHG) rules has placed great pressure on the commercial vehicle industry and has driven demand for innovative solutions. One potential solution, gasoline compression ignition (GCI), utilizes gasoline’s lower reactivity to promote partially premixed combustion and extract efficiency while reducing the PM-NOx trade-off curve. Gasoline’s volatility allows for the use of higher levels of exhaust gas recirculation (EGR), a key enabler of GCI combustion. In order to deliver higher levels of EGR while maintaining sufficient boost pressure, a tailored and efficient air-handling system is critical. This work presents the analysis-led development of a low-NOx GCI air-handling system including both turbocharger matching and EGR configuration for a prototype heavy-duty GCI engine based on a model year 2013 Cummins ISX diesel engine using low octane gasoline (RON80). In the analysis-driven development process, a 1D engine system-level analysis was closely coupled with closed-cycle 3D CFD GCI combustion development. Three different boost systems were investigated using a validated 1D engine model: 1) the production turbocharger; 2) an off-the-shelf single-stage waste-gate turbocharger; 3) a prototype single-stage variable geometry turbocharger. For each boost system, three EGR configurations were evaluated: 1) a high-pressure EGR route; 2) a low-pressure EGR route; 3) a dual-loop EGR route. The air-handling system performance was first investigated over five steady-state engine operating conditions extracted from the ramped modal cycle supplemental emissions test. Then, through cosimulation using a Simulink-based engine controls model, the best performing candidates under transient operation through the Heavy-Duty Federal Test Procedure certification cycle were identified. The production turbocharger, designed for 4–6 g/kWh engine-out NOx, suffered from low combined turbocharger efficiency under the low-NOx GCI thermal boundary conditions. The prototype 1-Stage variable geometry turbocharger, when used with a high-pressure EGR configuration, demonstrated higher combined efficiencies, while the waste-gate turbocharger showed the best results when used with a dual-loop EGR system. All low-pressure only EGR configurations were found to incur additional pumping penalties due to the need for a back pressure valve to drive sufficient EGR levels. In the transient test cycle analysis, the single-stage high-pressure EGR system was capable of delivering the target boost and EGR, while the off-the-shelf waste-gate turbocharger, with its higher mass inertia, showed slower turbine response and a resulting lag in boost response. Unsurprisingly, the dual-loop EGR system also suffered from delays in EGR delivery during engine acceleration. In summary, the prototype single-stage variable geometry turbocharger with a high-pressure EGR system produced the best performance over both the steady-state and transient engine cycles and was identified as the best candidate for the prototype low-NOx heavy-duty GCI engine.

Feedback Error Learning Control Using OS-ELM for SI Engine Airpath Systems

Abstract Currently, due to the stricter emission legislation, spark-ignition (SI) engine with low pressure exhaust gas recirculation (LP-EGR) has become a research hotspot. However, with the increasing complexity of engine, it is difficult to obtain sufficient control performance by conventional MAP control or PID control. This paper focuses on the airpath system of a SI engine with low pressure EGR, proposes a new model-based control method for the model of the airpath system based on the Feedback Error Learning control using online sequential-extreme learning machine (OS-ELM) as controller algorithm. In this paper, the airpath model has been built and effectiveness of the proposed control method has been confirmed on the model.

Modelling and Output Predictive Control of Engine Air Path Systems for Intake Fresh-air and Exhaust Gas Recirculation

This paper deals with the control problem of an engine air path system with low pressure exhaust gas recirculation (EGR). The considered air path system with low EGR can be modelled as a system with time-delays due to the transport delay of gas flow from EGR. It results in over intake fresh air, and thus it causes torque overshoot. An output predictive control system is designed for a time delay air path system in order to obtain the desired fresh air mass flow. In the considered system, the intake fresh air mass flow and the EGR rate are taken as the outputs, and the throttle valve and the EGR valve are considered as inputs of the system in this paper. A detailed air path system model with time-delay will also be derived for confirming the effectiveness of the proposed method through numerical simulations.

Health Monitoring of Aging Prone Powertrain Air and Fuel Path Uncertainties: EGR Valve Area, Mass Air-Flow Sensor Bias, and Injection Drift

Model-based airpath control systems rely on accurate Exhaust Gas Recirculation (EGR) valve flow models and unbiased sensor/actuator measurements. Due to component tolerance ranges, sooting/clogging, and sensor aging phenomena there is a need for online estimation of adaption parameters to ensure consistent engine-out emissions are achieved vehicle-to-vehicle. This paper addresses a joint estimation problem for the Factor of Effective Area (FEA) of High-Pressure (HP) and Low-Pressure (LP) EGR valves, the estimation of Mass Air-Flow (MAF) sensor bias as well as the estimation of injector’s drift. The adaptation is based on widely-accepted discrete-time Extended Kalman Filter (EKF) that combines the intake manifold pressure model with the measurement model of the total EGR flow (computed as a difference of engine charge flow model and biased MAF sensor) further combined with the MAF sensor and intake manifold pressure sensor measurement models. It is demonstrated for diesel engine equipped with dual HP/LP EGR valves that MAF sensor bias of a magnitude ±5% and injection drift of a magnitude ±1.5mg/st can be successfully identified together with the FEA parameters. WLTC data taken from an engine dynamometer show the emissions can be maintained at the same level for an engine with simulated offsets when compared to a nominal condition.

Model development and experimental validation of an exhaust brake supported dual loop exhaust gas recirculation on a medium duty Diesel engine

Due to the new European emission norms internal combustion engines have to comply stricter rules. The new norms contain new requirements that were not included in previous regulations for example the decreased temperature of the cold start or the real driving emission part. The emission cycles for passenger vehicles are completely news, the stricter emission norms for commercial vehicles will follow them within a few years. Despite the increasing spread of alternative transmission systems in road transport Diesel engines are going to be remain in commercial vehicles in the next decades due to their good torque and fuel consumption performance. The emission of Diesel engines can be kept low by several way: by the modification of combustion processes, or by exhaust gas after treatment. To comply future regulations both of them seems to be necessary. By exhaust gas recirculation systems alternative Diesel combustion processes can be realized which can provide lower nitrogen-oxide emission and in several operation points also lower fuel consumption. Exhaust gas recirculation systems also can support the thermal management of a Diesel engine. To utilize the advantages of the recirculated exhaust gases a complex system is necessary to get a freedom in control possibilities: duel loop exhaust gas recirculated systems supplemented with supporter valves on the intake or on the exhaust side. In this paper a pressure and mass flow rate based control oriented engine model will be presented which contains high and low pressure exhaust gas recirculation systems and both of them are supported by exhaust brakes. The model considers four balance volumes and it has five state variables. The model is validated by an engine dyno measurements on a medium duty Diesel engine.

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.

Model predictive air path control for a two-stage turbocharged spark-ignition engine with low pressure exhaust gas recirculation

Innovative air path concepts for turbocharged spark-ignition engines with exhaust gas recirculation impose high demands on the control due to nonlinearities and cross-couplings. This contribution investigates the control of the air and exhaust gas recirculation paths of a two-stage turbocharged spark-ignition engine with low pressure exhaust gas recirculation. Using exhaust gas recirculation at high loads, the in-cylinder temperature can be lowered, reducing the knock tendency, while at the same time preventing the need for the enrichment of the air/fuel ratio. Air and exhaust gas recirculation paths are cross-coupled and show different delay times. To tackle these challenges, a data-based two-stage model predictive controller is proposed: The target selector accounts for the overactuated system structure, while the dynamic controller adjusts the charging pressure and exhaust gas recirculation rate. The prediction model setup is based on a small amount of dyno-run measurement data. To ensure real-time capability, the model is kept as simple as possible. This allows for fast turnaround times of the algorithm, while maintaining the necessary accuracy in steady-state and transient operation. This study focuses on a two-stage control concept based on a target selector for optimal stationary control inputs and the dynamic controller considering the dynamic behavior of the air and exhaust gas recirculation paths. Subsequently, the control concept for the two-stage turbocharged spark-ignition engine with low pressure exhaust gas recirculation is validated via experimental tests under real-driving conditions on an automotive test track, using a prototype test vehicle. Results show that boost pressure as well as exhaust gas recirculation rate setpoints are met without overshoot and control deviation with settling times being close to the boundaries set by the hardware.

Gasoline engine performance simulation of water injection and low-pressure exhaust gas recirculation using tabulated chemistry

This work presents the assessment of direct water injection in spark-ignition engines using single cylinder experiments and tabulated chemistry-based simulations. In addition, direct water injection is compared with cooled low-pressure exhaust gas recirculation at full load operation. The analysis of the two knock suppressing and exhaust gas cooling methods is performed using the quasi-dimensional stochastic reactor model with a novel dual fuel tabulated chemistry model. To evaluate the characteristics of the autoignition in the end gas, the detonation diagram developed by Bradley and co-workers is applied. The single cylinder experiments with direct water injection outline the decreasing carbon monoxide emissions with increasing water content, while the nitrogen oxide emissions indicate only a minor decrease. The simulation results show that the engine can be operated at λ = 1 at full load using water–fuel ratios of up to 60% or cooled low-pressure exhaust gas recirculation rates of up to 30%. Both technologies enable the reduction of the knock probability and the decrease in the catalyst inlet temperature to protect the aftertreatment system components. The strongest exhaust temperature reduction is found with cooled low-pressure exhaust gas recirculation. With stoichiometric air–fuel ratio and water injection, the indicated efficiency is improved to 40% and the carbon monoxide emissions are reduced. The nitrogen oxide concentrations are increased compared to the fuel-rich base operating conditions and the nitrogen oxide emissions decrease with higher water content. With stoichiometric air–fuel ratio and exhaust gas recirculation, the indicated efficiency is improved to 43% and the carbon monoxide emissions are decreased. Increasing the exhaust gas recirculation rate to 30% drops the nitrogen oxide emissions below the concentrations of the fuel-rich base operating conditions.

Control of hybrid boosting in highly diluted internal combustion engines

A novel hybrid system enabling both flexible supercharging and limited torque assist is studied to mitigate transient response challenges of a turbocharged spark ignition engine equipped with low pressure exhaust gas recirculation. The hybrid system, called a power split supercharger (SC), is configured with a planetary gear set that splits the supercharging power between a small low-voltage electric motor and the engine crankshaft. The air path controller relies on the coordination of four actuators on the engine side and three low-level actuators on the hybrid boosting device. A decentralized control scheme is used in this work, in which the master–slave structure of the boost pressure controller decreases the turbo-lag associated with exhaust gas recirculation, while minimizing the SC operation for fuel economy. A vector reference governor is used to prevent compressor surge during engine tip-outs. In addition, the desired intake manifold pressure is modified to provide time for evacuating the exhaust gas recirculation and avoiding misfires when transitioning to low load, while the hybrid capability of the power split SC is used to recuperate the unwanted generated power. All controllers are validated on both a mean value engine model and a high-fidelity engine model. Practical challenges of implementing the vector reference governor to the highly nonlinear engine air path with pressure pulsations originating from the engine reciprocation are discussed and some solutions are proposed.

Development of an experimental test bench and a psychrometric model for assessing condensation on a low-pressure exhaust gas recirculation cooler

A test bench has been designed to assess condensation formation produced on the interior of a low-pressure exhaust gas recirculation cooler working with hot stream of humid air representing an engine warm-up stage, when its coolant starts from very cold conditions. An experimental campaign has been conducted with three different exhaust gas recirculation mass flow rates, four exhaust gas recirculation inlet temperatures and three different coolant initial temperatures, covering common conditions found in the low-pressure exhaust gas recirculation system of internal combustion engines under cold starts. The transient experimental results are analyzed and compared with a simple psychrometric condensation model, obtaining a good correlation and reproducing the trends of the condensation, even though an overprediction of the condensates of around 20%–40% exists due to the strong hypotheses assumed. The warm-up tests are most sensitive to the initial coolant temperature. For example, an engine starting at –10 °C ambient temperature could require 10 min to stop producing water in the low-pressure exhaust gas recirculation cooler, with an accumulated quantity during the warm-up of about 100 mL of condensates.

Advantages of using a cooler bypass in the low-pressure exhaust gas recirculation line of a compression ignition diesel engine operating at cold conditions

The low efficiency of the after-treatment systems during the cold start period of the internal combustion engines leads to excessive pollutant emissions levels. To reduce the nitrogen oxide emissions at these conditions, it could be necessary to use the high- and low-pressure exhaust gas recirculation strategies, even operating at low temperatures. This article evaluates the impact of using a low-pressure exhaust gas recirculation cooler bypass in a Euro 6 turbocharged diesel engine running under cold conditions (–7 °C). A new compact line fitted with a bypass system for the cooler is used with the aim of accelerating the engine warm-up process as compared to the original low-pressure exhaust gas recirculation line. The system is evaluated following two strategies, first performing exhaust gas recirculation without bypass and then performing exhaust gas recirculation bypassing the cooler. The results show that the activation the low-pressure exhaust gas recirculation from the engine cold start leads to a significant nitrogen oxide emissions reduction. Moreover, the bypass activation leads to increase the engine intake temperature, reducing the engine warm-up time and the CO emissions due to better combustion efficiency. However, the activation of the low-pressure exhaust gas recirculation at low temperatures could produce condensation and fouling deposits on the engine components affecting their life span. These phenomena are visualized using endoscope cameras in order to identify the condensation time and the final conditions of the elements. In addition, a chemical analysis of some condensates collected during the experiments and a comparison versus other species found in the literature is presented.