Search Results (18)

In this paper, a novel technical route, namely combining the low-pressure exhaust gas recirculation (LP-EGR) and variable compression ratio (VCR), is proposed to address the inferior fuel economy for marine dual-fuel engines of low-pressure gas injection in diesel mode. To validate the applicability of the proposed technical route, firstly, a zero-dimensional/one-dimensional (0-D/1-D) engine simulation model with a predictive combustion model DI-Pulse is established using GT-Power. Then, parametric investigations on two LP-EGR schemes, which is implemented with either a back-pressure valve (LP-EGR-BV) or a blower (LP-EGR-BL), are performed to qualitatively identify the combined impacts of exhaust gas recirculation (EGR) and compression ratio (CR) on the combustion process, turbocharging system, and nitrogen oxides (NOx)-brake specific fuel consumption (BSFC) trade-offs. Finally, an optimization strategy is formulated, and an optimization program based on response surface methodology (RSM)–particle swarm optimization (PSO) is designed with the aim of improving fuel economy while meeting Tier III and various constraint conditions. The results of the parametric investigations reveal that the two LP-EGR schemes exhibit opposite impacts on the turbocharging system. Compared with the LP-EGR-BV, the LP-EGR-BL can achieve a higher in-cylinder pressure level. NOx-BSFC trade-offs are observed for both LP-EGR schemes, and the VCR is confirmed to be a viable approach for mitigating the penalty on BSFC caused by EGR. The optimization results reveal that for LP-EGR-BV, compared with the baseline engine, the optimized BSFC decreases by 10.16%, 11.95%, 10.32%, and 9.68% at 25%, 50%, 75%, and 100% maximum continuous rating (MCR), respectively, whereas, for the LP-EGR-BL scheme, the optimized BSFC decreases by 10.11%, 11.93%, 9.93%, and 9.58%, respectively. Furthermore, the corresponding NOx emissions level improves from meeting Tier II regulations (14.4 g/kW·h) to meeting Tier III regulations (3.4 g/kW·h). It is roughly estimated that compared to the original engine, both LP-EGR schemes achieve an approximate reduction of 240 tons in annual fuel consumption and save annual fuel costs by over USD 100,000. Although similar fuel economy is obtained for both LP-EGR schemes, LP-EGR-BV is superior to LP-EGR-BL in terms of structure complexity, initial cost, maintenance cost, installation space requirement, and power consumption. The findings of this study provide meaningful theoretical supports for the implementation of the proposed technical route in real-world engines. Full article

Exhaust gas recirculation (EGR) systems, in addition to catalytic reactors, are now widely used in reciprocating internal combustion engines to reduce oxides of nitrogen (NOx) in the exhaust gases. They are characterized by the fact that part of the exhaust gas from the exhaust manifold is recycled and directed to the intake manifold through a special valve. This valve, depending on the current engine load and velocity, doses an appropriate amount of exhaust gas which, with each new charge, is fed to the individual engine cylinders. In addition, the positioning of the valve has a significant effect on the formation of nitrogen oxides in the exhaust gas from individual engine cylinders, which is due to the uneven distribution of exhaust gas into the intake manifold channels. Tests were carried out on a power unit equipped with a symmetrical intake manifold with a centrally located EGR valve. The article presents the results of tests on a system in which each cylinder was supplied with a separate EGR valve. This solution made it possible to charge each cylinder with the same mass of recirculated exhaust gas, which was dependent on engine velocity and load. The exhaust nitrogen oxides emissions were measured for the originally manufactured system and compared with the multi-valve system. The results confirmed the need for individual selection of the dose of recirculated exhaust gas for particular cylinders, as the multi-valve system equalized the levels of nitrogen oxides emissions in the exhaust gases coming from individual cylinders of the internal combustion engine. Full article

The exhaust gas recirculation (EGR) valve plays an important role in improving engine fuel economy and reducing emissions. In order to improve the positioning accuracy and robustness of the EGR valve under uncertain dynamics and external disturbances, this paper proposes a positioning servo system design for an electromotive (EM) EGR valve based on the Kalman filter. Taking a novel valve driven by a central winding limited angle torque motor (LATM) as the object, we have fully considered the influence of the motor rotor position and load current, as well as the magnetic field saturation and cogging effect, improved the existing LTAM model, and derived accurate torque expression. The parameter uncertainty of the above internal model and the external stochastic disturbance were unified as “total disturbance”, and a Kalman filter-based observer was designed for disturbance estimations and real-time feed-forward compensation. Furthermore, using non-contact magnetic angle measurements to obtain accurate valve position information, a position control model with real-time response and high accuracy was established. Numerous simulated and experimental data show that in the presence of ± 25% plant model parameter fluctuations and random shock-type disturbances, the servo system scheme proposed in this paper achieves a maximum position deviation of 0.3 mm, a repeatability of positioning accuracy after disturbances of 0.01 mm, and a disturbance recovery time of not more than 250 ms. In addition, the above performance is insensitive to the duration of the disturbance, which demonstrates the strong robustness, high accuracy, and excellent dynamic response capability of the proposed design. Full article

The motivation for conducting this research stems from the increasingly applied manipulations of emission control systems (ECSs), especially those in diesel passenger cars (PCs). The study aimed to investigate the influence of manipulations of exhaust gas recirculation (EGR) valves and a diesel exhaust fluid (DEF)-dosing system on the nitrogen oxide (NO_X) emissions of a Euro 6 diesel vehicle and, through the quantification of vehicles with manipulated ECSs, estimate the emissions of Euro 6 diesel PCs. Portable emissions measurement system (PEMS) measurements were performed on a Euro 6 diesel vehicle at a constant speed and on real driving emission (RDE) routes. The speed-dependent functions of the NO_X hot emission factor (EF) were calculated for seven different scenarios. The results showed that the NO_X EFs for the worst-case scenarios were more than two orders of magnitude higher than those where all ECSs were active. Applying the calculated EFs and the survey answers on the percentage of manipulated PCs to the Croatian Euro 6 diesel PC fleet, the results showed that the emission levels were up to 46.3% higher than the emissions calculated by the official computer program COPERT v5.6.5, with a tendency towards significantly higher values. The main conclusion is that vehicle manufacturers, policymakers, and the general public need to be informed about the enormous damage that in-use vehicles with manipulated ECSs cause to the environment and human health, in order to prevent such actions. Full article

An exhaust gas recirculation (EGR) valve is used to quickly and dynamically adjust the amount of recirculated exhaust gas, which is critical for improving engine fuel economy and reducing emissions. To address problems relating to the precise positioning of an electromotive (EM) valve under slowly varying plant dynamics and uncertain disturbances, we propose a servo control system design based on linear active disturbance rejection control (LADRC) for the EGR EM valve driven by a limited angle torque motor (LATM). By analyzing the structure of the LATM and the transmission, the dynamic model of the system is derived. In addition, to solve the problems caused by slowly varying plant dynamics and uncertain disturbances, we combine the effects of uncertain model parameters and external disturbances as the total disturbance, which is estimated in real time by an extended state observer (ESO) and then compensated. In addition, accurate angular information is obtained using a non-contact magnetic angle measurement method, and a high-speed digital communication channel is established to help implement a closed-loop position control system with improved responsiveness and accuracy. Simulation and experimental results show that the proposed servo system design can effectively ensure the precision and real-time performance of the EM valve under slowly changing plant dynamics and uncertain disturbances. The proposed servo system design achieves a full-stroke valve control accuracy of better than 0.05 mm and a full-stroke response time of less than 100 ms. The controlled valve also has good robustness under shock-type external disturbances and excellent airflow control capability. The repeatability of the airflow control is generally within 5%, and the standard deviation is less than 0.2 m³/h. Full article

The rising interest in the use of gaseous fuels, such as bio-methane and hydro-methane, in Heavy-Duty (HD) engines to reduce Greenhouse Gases pushed by the net-zero CO₂ emissions roadmap, introduced the need for appropriate strategies in terms of fuel economy and emissions reduction. The present work hence aims at analysing the potential benefits derived from the application of the cylinder deactivation strategy on a six-cylinder HD Natural Gas Spark Ignition (SI) engine, typically employed in buses and trucks. The activity stems from an extensive experimental characterisation of the engine, which allowed for validating a related 1D model at several Steady-State conditions over the entire engine workplan and during dynamic phases, represented by the World Harmonized Transient Cycle (WHTC) homologation cycle. The validated model was exploited to assess the feasibility of the considered strategy, with specific attention to the engine working areas at partial load and monitoring the main performance parameters. Moreover, the introduction in the model of an additional pipeline and of valves actuated by a dedicated control logic, allowed for embedding the capability of using Exhaust Gas Recirculation (EGR). In the identified operating zones, the EGR strategy has shown significant benefits in terms of fuel consumption, with a reduction of up to 10%. Simultaneously, an appreciable increase in the exhaust gas temperature was detected, which may eventually contribute to enhance the Three-Way Catalyst (TWC) conversion efficiency. Considering that few efforts are to be found in the literature but for the application of the cylinder deactivation strategy to Light-Duty or conventionally fuelled vehicles, the present work lays the foundation for a possible application of such technology in Natural Gas Heavy-Duty engines, providing important insights to maximise the efficiency of the entire system. Full article

While the original equipment manufacturers are developing engines that can withstand higher PCP, the methodology to maximize the thermal efficiency gain with different PCP limits is still not well-known or documented in the literature. This study aims to provide guidance on how to co-optimize air system parameters, compression ratio, and intake valve closing (IVC) timing of heavy-duty turbocharged diesel engines to enhance thermal efficiency with peak cylinder pressure (PCP) constraints. In this study, a one-dimensional turbocharged engine model is established and validated by experimental data. The effects of turbocharger efficiency, boost pressure, high-pressure exhaust gas recirculation (HP EGR) ratio, compression ratio (CR), and IVC timing on diesel engine efficiency are assessed under PCP constraints through parametric analysis. The results indicate that for enhancing engine thermal efficiency under limited PCP, an increment in boost pressure and CR, and late IVC timing compared to baseline is required. By multiple parameter optimization, the best parameter combination under different PCP constraints is proposed. At a PCP limit of 20 MPa, the combination of a compression ratio of 18.57, boost pressure of 298 kPa, and IVC timing of −95.2 °CA ATDC yields a 1.56% (absolute value) improvement in ITEn over the baseline condition. Raising the PCP limits from 20 MPa to 25 MPa requires increasing the compression ratio to 21.92, boost pressure to 308 kPa, and delaying the intake valve closing timing to −88.7 °CA ATDC, which results in an absolute improvement of 0.86% in ITEn. Baseline engine configuration is updated accordingly to validate the thermal efficiency improvement strategy at a 25 MPa PCP limitation. Experimental results demonstrate a 2.2% (absolute value) improvement in brake thermal efficiency and 1.98% (absolute value) improvement in overall energy efficiency. Full article

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 NO_x 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 NO_x 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. Full article

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

Although the exhaust gas recirculation (EGR) technology has been proven effective to decrease the marine engine’s nitrogen oxides (NOx) emissions, it is associated with a considerable fuel consumption increase and challenges to the engine–turbocharger matching. This study aims to parametrically optimise the EGR and turbocharging system settings of a large marine two-stroke engine with the objective of obtaining the highest engine efficiency whilst ensuring compliance with the prevailing NOx emissions limits. Two typical configurations of the investigated engine (baseline and alternative) are modelled in the GT-SUITE software. Parametric simulations are performed with EGR rates up to 40% along with cylinder bypass rates up to 50%, and the simulation results are analysed to quantify the impact of the engine operation with EGR on the performance and NOx emissions parameters. For the baseline engine configuration, the EGR rate increase considerably deteriorates the brake specific fuel consumption (BSFC), which is attenuated by opening the cylinder bypass valve. The optimal combinations of the EGR and cylinder bypass rates for each operating point are identified for both configurations. Following the comparative assessment between the two engine configurations, recommendations for the engine operating modes are proposed, leading to BSFC improvement in the region of 0.7 to 2.9 g/kWh. This study provides insights for the operational settings optimisation of two-stroke engines equipped with EGR systems, contributing towards the reduction of the associated environmental carbon footprint. Full article

Emission control devices such as selective catalytic reduction (SCR), exhaust gas recirculation (EGR), and scrubbers were installed in the compression ignition (CI) engine, and flow analysis of intake air and exhaust gas was required to predict the performance of the CI engine and emission control devices. In order to analyze such gas flow, it was inefficient to comprehensively analyze the engine’s cylinder and intake/exhaust systems because it takes a lot of computation time. Therefore, there is a need for a method that can quickly calculate the gas flow of the CI engine in order to shorten the development process of emission control devices. It can be efficient and quickly calculated if only the parts that require detailed observation among the intake/exhaust gas flow of the CI engine are analyzed in a 3D approach and the rest are analyzed in a 1D approach. In this study, an algorithm for gas flow analysis was developed by coupling 1D and 3D in the valve systems and comparing with experimental results for validation. Analyzing the intake/exhaust gas flow of the CI engine in a 3D approach took about 7 days for computation, but using the developed 1D–3D coupling algorithm, it could be computed within 30 min. Compared with the experimental results, the exhaust pipe pressure occurred an error within 1.80%, confirming the accuracy and it was possible to observe the detailed flow by showing the contour results for the part analyzed in the 3D zone. As a result, it was possible to accurately and quickly calculate the gas flow of the CI engine using the 1D–3D coupling algorithm applied to the valve system, and it was expected that it can be used to shorten the process for analyzing emission control devices, including predicting the performance of the CI engine. Full article

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. Full article

An exhaust gas recirculation (EGR) valve position control system requires fast response without overshoot, but the low control frequency limits control bandwidth and results in poor position response. A novel EGR valve position control scheme is proposed to improve the position response at low control frequency. This is based on the feedforward controller, but the feedforward control loop is implemented without the position pattern generator or derivative. The proposed method estimates the acceleration command through the relationship between the position controller output, the speed command and the speed limiter, and compensates the cascaded proportional-proportional integral (P-PI) controller. In this method, many operations are not required and noise due to derivative is not generated. This method can improve the position response without much computation and derivative noise at the low control frequency. Experimental results are presented to verify the feasibility of the proposed position control algorithm. Full article

This paper proposes a position control method for a low-cost exhaust gas recirculation (EGR) valve system for automotive applications. Generally, position control systems used in automotive applications have many restrictions, such as cost and space. The mechanical structure of the actuator causes high friction and large differences between static friction and coulomb friction. When this large friction difference occurs, the position control vibrates when the controller uses a conventional linear controller such as the P or PI controller. In this paper, we introduce an inexpensive position control method that can be applied under the high-difference-friction mechanical systems. The proposed method is verified through the use of experiments by comparing it with the results obtained when using a conventional control system. Full article

Variable valve mechanisms are usually applied to a gasoline combustion engine to improve its power performance by controlling the amount of intake air according to the operating load. These mechanisms offer one possibility of resolving the conflict of objectives between a further reduction of raw emissions and an improvement in fuel efficiency. In recent years, variable valve control systems have become extremely important in the diesel combustion engine. Importantly, it has been shown that there are several potential benefits of applying variable valve timing (VVT) to a compression ignition engine. Valve train variability could offer one option to achieve the reduction goals of engine-out emissions and fuel consumption. The aim of this study was to investigate the effects on part load combustion and emission performance of internal exhaust gas recirculation (EGR) by variable exhaust valve lift actuation using a cam-in-cam system, which is an electronically variable valve device with a variable inside cam retarded to about 30 degrees. Numerical simulation based on GT-POWER has been performed to predict the NO_x reduction strategy at the part load operating point of 1200 rpm in a four-valve diesel engine. A GT-POWER model of a common-rail direct injection engine with internal EGR was built and verified with experimental data. As a result, large potential for reducing NO_x emissions through the use of exhaust valve control has been identified. Namely, it is possible to utilize heat efficiently as recompression of retarded post injection with downscaled specification of the exhaust valve rather than the intake valve, even if the CIC V1 condition with a reduction of the exhaust valve has a higher internal EGR rate of about 2% compared to that of the CIC V2 condition. Full article