Heavy-duty Diesel Engine Research Articles

Data-driven machine learning model of a Selective Catalytic Reduction on Filter (SCRF) in a heavy-duty diesel engine: A comparison of Artificial Neural Network with Tree-based algorithms

The Selective Catalytic Reduction on Filter (SCRF) system is yet to be deployed in current heavy-duty diesel engine aftertreatment system. Due to the thermal, space and cost benefits of the SCRF, it could become a useful component of the after-treatment system of a heavy-duty diesel engine, as regulators continue to demand an even cleaner environment. Ammonia cross-sensitivity of NOx sensors at the post-SCRF location poses challenges in measuring NOx emission accurately at this location and in turn affects the NOx conversion efficiency calculations. Developing a model that could replace the NOx sensor helps to mitigate the ammonia cross-sensitivity challenge as well as provides a medium to measure post-SCRF NOx concentration and NOx conversion efficiency while saving the cost on NOx sensors. This work focuses on a data-driven approach to developing a model for predicting NOx conversion efficiency across the SCRF using Artificial Neural Network, Bootstrap Forest, and Boosted Tree methods. Further, the three modeling techniques were also compared for accuracy and computation cost.

Comparative study on combustion and emission characteristics of gas-to-liquid with diesel on a burner and a naturally aspirated compression ignition engine

ABSTRACT Due to the consumption of fossil fuels and the generation of harmful emissions by diesel engines, researchers are seeking alternative fuels for diesel, for example, gas-to-liquid (GTL). However, most studies on combustion and emission of GTL focused on the fuel burned on turbocharged heavy-duty diesel engines. The purpose of this study is to reveal the combustion, fuel economy, and emission characteristics of GTL by a burner and a naturally aspirated (NA), fuel direct injection compression ignition light-duty engine. Comparative experiments of the GTL to fossil diesel were carried out, respectively. The burner has good consistency with the diesel engine in revealing emission trends. The results of the burner test showed that GTL produced less flame smoke and its flame height was 5.3% lower than diesel. The results of the engine bench test revealed that the combustion and emissions of the GTL with diesel were significantly different. Compared to diesel, the ignition of GTL began earlier from 1.5°CA to2.5°CA though the combustion was slower in contrast to diesel. The diffusion combustion maximum pressure was considerably 4.8% higher and occurred earlier with 2.2°CA-3°CA, and the premixed combustion peak pressure of GTL was slightly beyond the diesel. The peak of premixed combustion heat release rate (HRR) for GTL was less than that of diesel by 18.9%. While the peak HRR of diffusion combustion was greater by 38.4%. The maximum PRR value of GTL was lower than that of diesel leading to soft combustion. In all test conditions, the brake specific fuel consumption of GTL averagely reduced by 4.7% against diesel, and the brake thermal efficiency was on average 4.3% higher. GTL engine can reduce regular emissions of carbon monoxide, hydrocarbons, nitrogen oxide (NOx), smoke, and particle number (PN) simultaneously. It is worth noting that GTL improved the trade-off issue of NOx and smoke, simultaneously reducing 18.8% NOx and 24.1% smoke on average. The experimental results reveal the GTL is an appropriate alternative fuel for light-duty diesel engine without modification of mechanical fuel system.

A Comparative Investigation of the Emissions of a Heavy-Duty Diesel Engine under World Harmonized Transient Cycle and Road Spectrum Cycle

In the present study, detailed comparative experiments on a heavy-duty diesel engine used in the world harmonized transient cycle (WHTC) and road spectrum reversely deduced cycle (RSRDC, which was derived from a road test) were carried out. Fuel consumption and gaseous and particulate pollutants, along with some engine operation parameters, were measured transiently; thus, specific emissions can be calculated. Results showed that the BSFC of WHTC and RSRDC was 201.8 and 210 g/kW·h, respectively, because the real road driving cycle (RSRDC) had wider operating point distributions and more points located in the low-efficiency zone relative to WHTC. Thus, WHTC operations exhibited higher raw CO (abundant CO formation needed a specific temperature threshold) and NOx but lower HC. Furthermore, with aftertreatment, all pollutants met the newest China regulation limit. Finally, transient emissions were analyzed in detail. Although the specific emissions of some pollutants were similar in value for both cycles, transient processes may largely be different. Therefore, the current study is meaningful, and we not only provide broad and detailed information but also directly compare two types of operations (one is a real road driving cycle) in the laboratory: this is rarely discussed in the literature.

Experimental study on the transient-state performance of diesel engines at different speeds using the synergistic regulation of VGT and VVT

Heavy-duty diesel engines, the heat engines with the highest thermal efficiency, usually operate under transient conditions. Thus, it is important to study the transient performance of heavy-duty diesel engines. This paper aims to solve the problems of combustion deterioration, poor response, and emission deterioration caused by the mismatch between the air intake response and the fuel system under the strong transient condition of sudden loading of 1 s under constant speed. In this paper, an experimental study on the transient performance at different speeds under the coordinated regulation of a variable geometry turbocharger (VGT) and variable valve timing (VVT) is conducted. The study found that the transient torque response is affected by combustion in the cylinder and pump work. During the low-speed transient process, due to reduced airflow and pumping losses, the VVT is switched off while the VGT delay is increased to improve air response. Consequently, the mixture in the cylinder is fully burned, and improved transient performance is obtained. In the high-speed transient process, the engine air intake flow is improved. Through the VVT is ON at the appropriate time and the VGT hysteresis control, the pumping loss can be effectively reduced, and excellent transient performance can be achieved to ensure the fast response of the in-cylinder charge. Given sudden loading from 10% to 100% within 1 s under a high speed of 1600 r/min, the VVT switches on with a 0.15 s delay, and the VGT is controlled with a 0.4 s delay. A torque response of 0.82 s can be achieved, and the soot peak value is reduced by 66.26%, and the accumulated value of soot is reduced by 46.91%. At a low speed of 1000 r/min, given sudden loading from 10% to 100% within 1 s, the 0.6 s VGT delay can reduce the accumulated value of soot by 78.57% and 56.22% compared with delays of 0.2 and 0.4 s.

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.

Emission Characteristics of Heavy-Duty Vehicle Diesel Engines at High Altitudes

The aim of this study was to accurately quantify the emission characteristics of pollutants at different altitudes. We used an intake and exhaust altitude simulation system that could simulate the intake and exhaust pressures of a national sixth vehicle diesel engine at different altitudes. Experimental research was conducted on the World Harmonized Transient Cycle (WHTC) and World Harmonized Steady State Cycle (WHSC) of the diesel engine. The results showed that carbon monoxide (CO) emissions increased with the altitude at full load, but their rates were significantly reduced at low speed (800 rpm), increasing by 0.0084–0.665 ppm/m. Hydrocarbon (HC) emissions showed an initial decreasing and then increasing trend, with a rise of up to 30%. Nitrogen oxides (NOx) showed a linear decreasing trend, especially at low speed. With the increase in altitude, the cycle work of the diesel engine decreased in a non-linear manner, and the decrease became more pronounced above 3000 m. The raw emission results of the WHTC and WHSC tests also revealed that CO increased exponentially, NOx decreased slightly and then increased rapidly, HC increased linearly, and the emissions of all pollutants deteriorated significantly above 3000 m. The exhaust emission results of the WHTC and WHSC tests showed that the CO emission showed an initial decreasing and then increasing trend with the elevation of the altitude, approximately 15 ± 5 mg/kWh. HC emissions showed an increasing trend, with HC emissions of 3 – 6 mg/kWh for the WHTC and 1 – 2 mg/kWh for the WHSC. NOx emissions did not follow any obvious rule, while the particulate matter (PM) tended to increase and then decrease with the elevation of the altitude. In relation to the current emission standards, the limit value margin for CO and HC exhaust emissions is greater than 95% and the limit value margin for PM emissions is greater than 88% at an altitude of 4000 m. The NOx emission limit is greater than 87% (within 3000 m), but there is a risk of exceeding the limit above 3000 m. The second sampling data from the WHTC and WHSC showed that the raw emissions of the engine were higher in the high-altitude area than in the low-altitude area, but the change law of the exhaust emissions was not obvious, and the levels of both emissions were low.

Feasibility study on application of low-grade fuels (naphtha and ethanol) in blended-fuel- and convergence-combustion modes

Since electrification is difficult in the sector where heavy-duty diesel engines are used, research is still needed to improve air pollutants. In addition, it is necessary to search for fuel to solve the depletion of fossil fuels and to study appropriate combustion methods according to fuel characteristics. In this study, naphtha or ethanol was selected as a fuel that could replace a certain fraction of diesel fuel. This study aims to compare both methods of supplying and burning naphtha or ethanol with diesel. The method of supplying naphtha or ethanol blended directly with diesel and burning it is suitable for naphtha. Since ethanol has a lower heating value, blended-fuel combustion mode with ethanol reduces IMEPnet. However, this method of separate injection and burning is only suitable for ethanol. When naphtha is utilized in convergence combustion, a wetting phenomenon arises due to its limited evaporation characteristics, leading to a reduction in fuel delivery. The NOx reduction rate was higher in the convergence combustion mode than that in the blended-fuel combustion mode. However, both the combustion methods led to an increase in the THC and CO emissions.

Developing a Computational Fluid Dynamics-Finite Element Method Model to Analyze Thermal-Mechanical Stresses in a Heavy-Duty Medium-Speed Diesel Engine Piston During Warm-Up

Abstract Pistons play a vital role in internal combustion engines, affecting both performance and reliability, and are subjected to intense thermal-mechanical loads that have become more challenging due to improved engine efficiency and power. This study examines the thermal and mechanical stress experienced by a piston in a heavy-duty medium-speed diesel engine during warm-up. The heavy-duty diesel engines are typically used in heavy trucks, locomotives, and ships. A combination of computational fluid dynamics, finite element method, and matlab was used to consider factors such as oil temperature and flowrate, coolant temperature, component temperature, and boundary conditions during engine transient conditions. The results highlight the significant variations in the thermal and mechanical stress on the piston, particularly in the piston head under different warming-up conditions. It is noted that the variation in oil temperature is a crucial factor affecting the thermal stress on the piston. Low oil temperature can result in reduced heat exchange coefficient and inadequate cooling of the piston due to low flowrate of the cooling oil. During engine warm-up, both thermal and combined stresses reach maximum values and then decrease when the engine reaches stable operating conditions. By selecting appropriate warming-up modes, the quality of the warm-up process and the strength and longevity of the engine could be improved. This study also provides useful insights for technicians to prevent critical conditions that may damage the piston and reduce its strength and lifespan.

Potential of Variable Geometry Radial Inflow Turbines as Expansion Machines in Organic Rankine Cycles Integrated with Heavy-Duty Diesel Engines

This work evaluates the feasibility of utilizing an organic Rankine cycle (ORC) for waste heat recovery in internal combustion engines to meet the stringent regulations for reducing emissions resulting from the combustion of fossil fuels. The turbine is the most crucial component of the ORC cycle since it is responsible for power production. In this study, a variable geometry radial inflow turbine is designed to cope with variable exhaust conditions. A variable geometry turbine is simply a radial turbine with different throat openings: 30, 60, and 100%. The exhaust gases of a heavy-duty diesel engine are utilized as a heat source for the ORC system. Different engine operating points are explored, in which each point has a different exhaust temperature and mass flow rate. The results showed that the maximum improvements in engine power and brake specific fuel consumption (BSFC) were 5.5% and 5.3% when coupled to the ORC system with a variable geometry turbine. Moreover, the variable geometry turbine increased the thermal efficiency of the cycle by at least 20% compared to the system with a fixed geometry turbine. Therefore, variable geometry turbines are considered a promising technology in the field and should be further investigated by scholars.

A computational parametric study of ducted fuel injection implementation in a heavy-duty diesel engine

Experiments have shown that ducted fuel injection (DFI) effectively reduces soot emissions from direct-injection diesel engines. Although many computational studies have evaluated DFI’s spray development and soot reduction mechanisms in constant volume chambers, only limited computational work on internal combustion engines exists. The DFI duct assembly changes the engine’s in-cylinder flow, spray, and combustion development. Therefore, current production engine designs might not be optimal for achieving the best engine performance with DFI. This work conducted an extensive numerical study to evaluate how parameter changes affect DFI performance. The parameters include swirl ratio, piston geometry, compression ratio (CR), number of injector orifices, split injection strategy, and exhaust gas recirculation (EGR) in a heavy-duty diesel engine utilizing DFI. The combustion and soot emission data from the Sandia compression ignition optical research engine were used for model validation. Simulations showed that an increased swirl ratio resulted in more intense jet flame-piston interaction, slowing down the combustion heat release during the late combustion stage and leading to lower indicated thermal efficiency (ITE) due to higher exhaust losses. A piston-bowl design with a reentrant inner piston edge yielded the highest thermal efficiency, due to the reduced cylinder head heat transfer loss. Additional injector orifices led to higher efficiency owing to a more advanced combustion phasing. Nevertheless, the maximum pressure rise rate (MPRR) and oxides of nitrogen (NOx) emissions also increased with the number of injector orifices due to more rapid heat release and higher combustion temperature. Implementation of a split injection strategy combined with a higher EGR rate effectively inhibited the excessive MPRR and NOx formation. In general, the study concluded that DFI is not sensitive to most parameter changes but will benefit from future parameter optimization.

Thermal Load Analysis of Piston Damaged by Wall-Wetting Combustion in a Heavy-Duty Diesel Engine

Piston damage is a frequent problem of engine durability and plays an important role in an engine’s performance design. Recently, a large amount of piston erosion has occurred in a series of heavy-duty diesel engines. To investigate the reason for the piston erosion, a study of the computational fluid dynamics (CFD) of the combustion process in the cylinder and finite element analysis (FEA) of piston was carried out under different initial temperatures. The results show that when the initial temperature decreases from 380 K to 307 K, the mass of wall-wetting increases by 73%, and the maximum combustion pressure increases from 8.1 MPa to 11 MPa; when the initial temperature decreases from 350 K to 328 K, the highest temperature at the throat of the valve pocket increases by nearly 100 K, doubling the temperature fluctuation; and in the case of 328 K, areas exceeding 700 K are concentrated on the top surface of the piston, and the temperature gradient in the depth direction of the throat position decays rapidly.

Experimental investigation on the characteristics of ammonia storage for heavy-duty diesel engine SCR catalyst

The ammonia storage characteristics were studied experimentally in two stages before and after shutting off the urea injection on a full-size Cu-based zeolite SCR catalyst. The experiment was conducted under the engine operating conditions with exhaust temperatures of 180, 220, 260, 300, 340, and 380 ℃. The variations of the ammonia storage amount, NOx conversion efficiency, and ammonia slip were separately investigated within the period of ammonia storage and consumption process. The results indicate that the maximum ammonia storage is only 10 g at 180 ℃, but around 43 g at 220 ℃. The maximum ammonia storage decreases with the increase of exhaust temperature over 220 ℃, which drops from 35 g at 260 ℃ down to below 13 g at 380 ℃. The most extended duration of 8082 s on the ammonia storage process occurred at the exhaust temperature of 220 ℃, mainly due to the deposit formation. The time width of the ammonia storage process is shortened with the exhaust temperature increasing over 220 ℃. The maximum NOx conversion efficiency is 80% at the temperature of 180 ℃ and 100% when the temperature rises to 220 ℃ or above. The higher temperature can improve the catalyst activity to supply more activated ammonia reacting with NOx. However, it promotes further ammonia slip. The ammonia storage and exhaust temperature are the main factors in the NOx conversion performance in the SCR catalyst. When the temperature is below 220 ℃, the NOx conversion efficiency strongly depends on the ammonia storage and increases with its amount. With the temperature further rising to 220℃ and above, the impact of the exhaust temperature on NOx conversion efficiency gradually increases.

Crank angle-resolved mass flow characterization of engine exhaust pulsations using a Pitot tube and thin-wire thermocouples

Characterizing pulsating flow in high-temperature, high-pressure engine exhaust gas is crucial for the development and optimization of exhaust energy recovery systems. However, the experimental investigation of engine exhaust pulses is challenging due to the difficulties in conducting crank angle-resolved measurements under these unsteady flow conditions. This study contributes to characterizing mass flow pulses from an isolated cylinder exhaust of a heavy-duty diesel engine using a single-pipe measurement system, developed for pulsating flow measurement. A Pitot tube-based approach is adopted to measure exhaust mass flow pulsations, complemented by fast temperature measurements obtained using customized unsheathed thin-wire thermocouples. The on-engine experiment is performed by isolating the in-cylinder trapped mass and the valve opening speed to produce different exhaust pulse waveforms. The adopted approach’s sensitivity in resolving instantaneous mass flows is evaluated analytically and experimentally, considering attenuated temperature measurement effects. Based on exhaust flow measurements, mass flow pulses are analyzed with regard to blow-down and scavenge phases. Under the load sweep, the main waveform change occurs during the blow-down phase, with pulse magnitude increasing with the load. In contrast, as the engine speeds up with a comparable trapped mass, the exhaust mass distribution in the blow-down phase decreases from 75.5% at 700 rpm to 41.9% at 1900 rpm. Additionally, it is observed that cycle-to-cycle variations in mass flow pulses align with combustion stability during the blow-down phase and are predominantly influenced by gas-exchange processes during the scavenge phase.

LNG 이종연료 운전이 상업용 디젤 엔진의 출력 및 배출가스 특성에 미치는 영향

In order to additionally supply LNG to a heavy-duty commercial diesel engine, a dual fuel system was installed; engine power and exhaust gas emissions while operating in the ‘ND-13 mode’, in accordance with the notice from the Ministry of Environment, were investigated. The feasibility of retrofitting the dual fuel system and plans based on mixture rate, power, and emission reduction to enable commercialization were evaluated. The engine power and torque values were within ±5% of the values for the existing engine; these were within the legal modification range. In case of exhaust gas emissions, the decrease in CO 2 emission due to the increase in load was apparent; it was reduced by 15.3%. NO X emission decreased by 58%; this could be attributed to the decrease in combustion temperature owing to water injection. THC and CO increased significantly, possibly due to the reduced combustibility of natural gas owing to bulk quenching, water injection, and the absence of catalysts. Additional research focused on modification of mapping values and installation of oxidation catalysts to improve the combustion performance of the system, is warranted.

Advances in Vehicle and Powertrain Efficiency of Long-Haul Commercial Vehicles: A Review

Mitigating CO2 emissions from long-haul commercial trucking is a major challenge that must be addressed to achieve substantial reductions in greenhouse gas (GHG) emissions from the transportation sector. Extensive recent research and development programs have shown how significant near-term reductions in GHGs from commercial vehicles can be achieved by combining technological advances. This paper reviews progress in technology for engine efficiency improvements, vehicle resistance and drag reductions, and the introduction of hybrid electric powertrains in long-haul trucks. The results of vehicle demonstration projects by major vehicle manufacturers have shown peak brake thermal efficiency of 55% in heavy-duty diesel engines and have demonstrated freight efficiency improvements of 150% relative to a 2009 baseline in North America. These improvements have been achieved by combining multiple incremental improvements in both engine and vehicle technologies. Powertrain electrification through hybridization has been shown to offer some potential reductions in fuel consumption. These potential benefits depend on the vehicle use, the details of the powertrain design, and the duty cycle. To date, most papers have focused on standard drive cycles, leaving a research gap in how hybrid electric powertrains would be designed to minimize fuel consumption over real-world drive cycles, which are essential for a reliable powertrain design. The results of this paper suggest that there is no “one-size-fits-all” solution to reduce the GHGs in long-haul trucking, and a combination of technologies is required to provide an optimum solution for each application.

An Explainable Prediction Model for Aerodynamic Noise of an Engine Turbocharger Compressor Using an Ensemble Learning and Shapley Additive Explanations Approach

In the fields of environment and transportation, the aerodynamic noise emissions emitted from heavy-duty diesel engine turbocharger compressors are of great harm to the environment and human health, which needs to be addressed urgently. However, for the study of compressor aerodynamic noise, particularly at the full operating range, experimental or numerical simulation methods are costly or long-period, which do not match engineering requirements. To fill this gap, a method based on ensemble learning is proposed to predict aerodynamic noise. In this study, 10,773 datasets were collected to establish and normalize an aerodynamic noise dataset. Four ensemble learning algorithms (random forest, extreme gradient boosting, categorical boosting (CatBoost) and light gradient boosting machine) were applied to establish the mapping functions between the total sound pressure level (SPL) of the aerodynamic noise and the speed, mass flow rate, pressure ratio and frequency of the compressor. The results showed that, among the four models, the CatBoost model had the best prediction performance with a correlation coefficient and root mean square error of 0.984798 and 0.000628, respectively. In addition, the error between the predicted total SPL and the observed value was the smallest, at only 0.37%. Therefore, the method based on the CatBoost algorithm to predict aerodynamic noise is proposed. For different operating points of the compressor, the CatBoost model had high prediction accuracy. The noise contour cloud in the predicted MAP from the CatBoost model was better at characterizing the variation in the total SPL. The maximum and minimum total SPLs were 122.53 dB and 115.42 dB, respectively. To further interpret the model, an analysis conducted by applying the Shapley Additive Explanation algorithm showed that frequency significantly affected the SPL, while the speed, mass flow rate and pressure ratio had little effect on the SPL. Therefore, the proposed method based on the CatBoost algorithm could well predict aerodynamic noise emissions from a turbocharger compressor.

Interfacial microstructure and mechanical properties of rotary inertia friction welded dissimilar 422 martensitic stainless steel to 4140 low alloy steel joints

In this work, dissimilar rotary inertia friction welds between 422 martensitic stainless steel and 4140 martensitic low-alloy steel were made to fabricate prototype heavy-duty diesel engine pistons. The influence of the inertia friction welding process and post weld heat treatment (PWHT) temperature on the interfacial microstructure evolutions and corresponding effects on mechanical properties of the 422/4140 welds were evaluated in detail. Carbon diffused from the 4140 side to the 422 side during PWHT at 650 °C for 1.5 h, causing the formation of a hard carbide-rich layer on the 422 side, and a softer but discontinuous C-depleted layer the 4140 side. PWHT at 700 °C for 1.5 h greatly accelerated C diffusion across the interface relative to 650 °C, resulting in a thicker hard carbide-rich layer and a relatively thick and continuous layer of coarse C-depleted grains (ferrite) on the 4140 side. In addition, the PWHT temperature greatly influenced the tensile properties and fracture behavior of the welds, with the 650 °C PWHT-ed samples failing predominately in a ductile manner in the 4140 heat affected zone during tensile testing. Conversely, the 700 °C PWHT specimens exhibited a strength reduction compared with the 650 °C PWHT specimens because of additional coarsening of the interfacial ferrite layer and softening of the base materials during PWHT, with brittle fracture between the hard and soft layers the predominate failure mechanism. Based on the findings, a reduced PWHT temperature and/or time, minimizing the hardness differential of the base metals, and pre-heating the 422 steel prior to welding are the potential pathways to achieve a more optimal balance between desirable tempering and stress relief of the weld microstructure and undesirable C migration across the weld interface, and to reduce the strength mismatch across the weld.

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.

Study on the Effects of Exhaust Gas Recirculation and Fuel Injection Strategy on Transient Process Performance of Diesel Engines

To meet increasingly stringent emission regulations, this study investigates the transient process of a heavy-duty diesel engine equipped with a two-stage turbocharger. The study focuses on analyzing the impact of the EGR system and fuel injection strategy during a transient process of a load increase (20% to 100% in 1 s) at a constant speed (1300 rpm). The research results showed that delaying the opening time of the high-pressure EGR valve from 0.1 s to 0.5 s reduces peak carbon soot emissions by 51.3%, with only a 3.13% increase in NOx emissions. By extending the high-pressure exhaust gas recirculation mixing length, the issue of an excessively high fuel–oxygen equivalence ratio caused by uneven exhaust gas mixing in individual cylinders can be avoided, resulting in a maximum reduction of 47.0% in peak soot emissions. Building on exhaust gas recirculation optimization, further modifications to the main and post-injection strategies led to a 28.1% reduction in soot emissions, a 4.73% decrease in peak NOx emissions, and a minor increase of 1.87% in the indicated fuel specific consumption compared to the single-injection strategy. The significant reduction in soot emissions will provide benefits for public health and environmental sustainability.

Design of an Optimum Compact EGR Cooler in a Heavy-Duty Diesel Engine towards Meeting Euro 7 Emission Regulations

Exhaust gas recirculation (EGR) has been an efficient emission treatment strategy employed in internal combustion engines (ICEs) to cope with NOx emission limits since the introduction of Euro 4 regulations for heavy-duty commercial vehicles. A portion of the exhaust gas is fed back into the intake port, replacing O2 in the fresh air with inert CO2 from the exhaust gas, resulting in a reduction in the combustion temperature and, hence, a reduction in NOx emissions. Considering the high exhaust temperature, this process increases the charge mixture temperature and degrades the volumetric efficiency of the engine. EGR coolers have been introduced as vital parts of EGR exhaust treatment systems with the aim of reducing the intake port temperature to increase volumetric efficiency and further reduce combustion temperatures. EGR coolers are heat exchangers (HXs) that generally employ engine coolant to reduce the EGR temperature with effectiveness values around 0.7~0.85 and downgrade with engine usage owing to soot deposition. Increasing the effectiveness of the EGR cooler has a positive effect on engine volumetric efficiency and reduces NOx, particulate matter (PM), and fuel consumption. The current study involved the design of a microchannel HX for a 500 PS heavy-duty Euro 6 diesel engine EGR cooler. The mechanical and thermal-hydraulic design calculations of the proposed HX were performed using Mathematica software. The optimum HX dimensions for the required boundary conditions were determined, and the performance of the EGR cooler was analyzed for the current and proposed options. Furthermore, Diesel-RK software was used to model the engine performance with NOx, PM, CO2 emissions, and fuel consumption predictions. The results show that the newly proposed microchannel HX design improves NOx, PM, and specific fuel consumption by 6.75%, 11.30%, and 0.65%, respectively.