Intake Manifold Pressure Research Articles

Experimental investigation on backfire occurrence, duration and termination in a hydrogen-fueled automotive spark ignition engine

The present study investigates the occurrence, duration, and termination of backfire in a hydrogen-fueled automotive spark ignition engine. Backfire is a pre-ignition phenomenon that originates from the cylinder and the flame travels towards the intake manifold of the engine during the suction stroke. A high-speed camera was used to capture the real-time backfire images during the engine running. The simultaneous acquiring of the intake manifold and in-cylinder pressure was used to define the origin, duration, and termination of backfire. The probability of backfire occurrence rises with the increase in torque at constant speed, the increase in speed (at constant torque), high equivalence ratio, and the increase in torque with the decrease in speed (at constant brake power). The critical exhaust gas temperatures (EGT) identified for backfire initiation are in the range of 765 °C to 955 °C for speeds from 2000 rpm to 4900 rpm. A correlation of backfire occurrence number (BON) for the prediction of backfire occurrence was developed using experimental results, where BON greater than or equal to zero, indicates backfire occurrence. The backfire is characterized using backfire ignition delay, expansion, convergence and termination. The average backfire propagation velocity calculated using high-speed images is found to be 179.3 m/s corresponding to a Mach number of 0.52 at an equivalence ratio of 0.5 and hence, backfire under varied speed can be characterized as deflagration. Simultaneous acquiring of pressure was found reliable approach for calculating backfire propagation velocity. Lastly, backfire was suppressed using forced air induction at a reactant velocity of 4.5 m/s. This study’s results could be useful for the prediction of backfire occurrence and backfire velocity in hydrogen-fueled engines.

LQTI boost pressure and EGR rate control of a diesel air charge system with eBoost assistance

Turbocharged diesel engines often suffer significant response delay due to so-called turbo-lag, especially engines with large displacement. For this reason, many technologies have been developed to reduce turbo-lag. This paper develops a coordinated control strategy for a diesel engine equipped with an eBoost (electrical compressor) system to significantly reduce turbo-lag. A multiple-input and multiple-output (MIMO) Linear Quadratic Tracking with Integral (LQTI) control strategy, along with its scheduling logic, is developed for the Ford 6.7 L 8-cylinder diesel engine equipped with a variable geometry turbocharger (VGT), exhaust gas recirculation (EGR), and added eBoost along with a bypass valve. Note that the existing production engine does not have an eBoost and bypass valve. Multiple model-based LQTI controllers were designed at different engine operational conditions based on the associated linearized models, and the control outputs are scheduled based upon the engine load condition and bypass valve position. The developed control strategy is validated in both simulation and experimental studies, and the test results show a reduction in engine response time by up to 81.36% in terms of reaching target intake manifold (boost) pressure following a load step-up, compared with the production configuration (without eBoost and bypass valve) with no significant impact on NOx emissions.

VACUUM MUFFLER AS A MEANS OF REDUCING THE EXTERNAL NOISE LEVEL OF THE KOZAK-7 ARMORED CAR

An important characteristic of military equipment is the level of camouflage properties. Among the methods of masking, an important role is played by reducing the external noise of military equipment. In this work, masking itself by reducing external noise will be considered. The Kozak-7 armored combat wheeled vehicle (hereinafter referred to as an armored car) was chosen as the object of the study. On the basis of the Kozak-7 armored car, a line of special vehicles can be developed: command and headquarters, control points, anti-tank complexes, medical, etc. This armored car, like most cars, has several main sources of noise, which together create its external noise. Exhaust gas noise is the most powerful component of external noise. Appropriate mufflers are used to reduce this type of noise. A highly efficient noise muffler, the so-called vacuum, has been developed, the principle of operation of which is to artificially create a vacuum with the help of a pumping unit directly in the muffler and in the inlet and outlet nozzles at the moment when the exhaust gases leave the engine, which makes it impossible for the latter to create acoustic noise. The dependence of the working time of the working cylinder of the muffler on the frequency of rotation of the engine crankshaft, the working volume of the engine, the volume of the working cylinder, the pressure and temperature in the engine intake manifold, the temperature of the exhaust gases, etc. This dependence will make it possible to determine the optimal parameters and limits of possibilities for the application of the described vacuum muffler system. Calculations made for an engine with a working volume of 5 liters show that at a rotation frequency of 2000-2500 min-1, the working time does not exceed ~ 0.05 s. This means, in turn, that the speed of the valves should be of the order of 0.01 s. Calculations of the efficiency of the pumping unit were made, which showed that for the efficient pumping of exhaust gases, and even more so to create sufficient vacuum in the exhaust system, the volume performance of the pumping unit must exceed the volume performance of the engine (for the case of theoretical one-hundred percent noise suppression of exhaust gases, which is not necessary in practice – at least several times). A forecast of the dependence of the external noise level of the Kozak-7 armored car on the speed of movement with the existing silencer and with the developed one was made.

Study of the effect of ignition crank angle and mixture composition on the performance of a spark-ignition engine fueled with ethanol

The publication presents the results of the measurements of the operating parameters of a spark-ignition engine fueled with 95-octane unleaded gasoline (ES95) and ethyl alcohol, approx. 92%. The measurements were carried out at a constant load: an engine speed of 1,500 rpm and a constant pressure in the intake system - MAP=0.45 bar. For each type of fuel, the measurements were carried out in two series for two variables. The ignition crank anglewas varied in the range of 0˚÷40˚ and the mixture composition λ in the range of 0.85÷1.25. The recorded engine performance parameters included torque, intake manifold pressure, intake air temperature, exhaust gas temperature and temporal fuel consumption; and exhaust gas composition was examined in terms of carbon monoxide, hydrocarbons and nitrogen oxides. The study showed that an ethanol-fueled engine has lower average efficiency compared to a gasoline one. The highest efficiency for ethanol was obtained for rich mixtures in the range λ=0.85÷1.0 and at high ignition advance angles. The use of alcohol fuel showed a very favorable effect on the composition of exhaust gas and a significantly lower content of harmful exhaust components was demonstrated. For the same operating points, carbon monoxide content was reduced by an average of 15%, and hydrocarbons and nitrogen oxides by an average of 80%.

Finite-frequency fuzzy fault-tolerant static output feedback H∞ control for Diesel engine air-path system

This paper focuses on the design of H∞ finite-frequency (FF) fault-tolerant static output feedback (FTSOFC) problem of Diesel engine air-path system with consideration of external disturbances and actuator faults. Initially, a Diesel engine air-path nonlinear model is described by Takagi-Sugeno (T-S) fuzzy model based descriptor approach. The aim is to regulate intake and exhaust manifold pressures to the desired reference pressures by controlling the Geometry Turbine (VGT) and Exhaust Gas Recirculation (EGR) valves. Then, the robust integrator-based control strategy is developed to track the desired reference signals despite the presence of disturbances and actuator faults. By using the extended Generalized Kalman Yakubovich Popov (GKYP) lemma, Lyapunov functions and independent slack matrices, sufficient conditions are established to ensure both the good tracking of reference pressures and the prescribed H∞ performance with FF domain of the fuel flow variation and actuator faults. Finally, simulation results are given to demonstrate the effectiveness of the proposed approach.

Effects of hydrogen peroxide on the combustion and emissions of an ethanol/gasoline combined injection engine under different excess air ratios

Hydrogen peroxide (H2O2) can prompt hydroxyl radicals and chain reactions in the combustion process. Compared with the research on compression ignition engines, the effects of H2O2 were less studied in spark ignition (SI) engines. In this paper, 30 % laboratory-grade H2O2 (H2O2-30 %) was utilized to obtain the H2O2-ethanol blend, which was applied to a direct injection system in a combined injection SI engine. Gasoline was used for the port injection system. The effects of H2O2-30 % ratio (H2O2r) = 0 %, 5 %, 10 %, 15 % and 20 % on combustion and emission performance of an ethanol/gasoline engine were explored at three excess air ratios (λ = 0.9, 1 and 1.2). Engine operating condition was set at engine speed = 1500 rpm and intake manifold pressure = 49.5 kPa. The results showed that H2O2-30 % could reduce the Tmax and Pmax, and extend CA0-10, CA50 and CA10-90. The inhibition effects of water on combustion performance can be alleviated due to the hyperactive H2O2 at the H2O2r > 5 %. Optimal H2O2r increased engine IMEP by 0.14 bar, 0.11 bar and 0.05 bar, and reduced BSHC and BSCO by 30.5 %, 36.6 %, 31.6 % and 17.9 %, 32.1 % and 40.8 %, respectively. BSNOx were reduced by an average of 38.0 %, 28.8 % and 42.2 % at λ = 0.9, 1 and 1.2, respectively.

Develop an ECU for Controlling Fuel Injectors Using Arduino and LabVIEW for Training Purposes

The technology of electronic motor control is now advancing rapidly. Many studies and applications have been done on automatic system control in vehicles. The automatic fuel injection control system for automobile engines is a unique area of study and instruction in universities. The engine will run more efficiently, use less fuel, and emit fewer emissions when the fuel injection system is precisely controlled. It is challenging for student research to evaluate improvements to engine performance on real engine controller units (ECUs). Since their ECUs are already set for specific automotive duties, it is challenging to run tests by modifying the ECU's input parameters. In this study, a programmable ECU was created to explore the characteristics of the fuel injection system using the open-source, low-cost Arduino microcontroller. Using LabVIEW software, the algorithmic program computes and graphically simulates the injector characteristics. This study determines the injector opening time and fuel volume injected using the data from the intake manifold pressure sensor, lambda signal, engine temperature, throttle position, engine speed, and exhaust gas sensor. The primary objective of this study was not to replace a real ECU. It was more beneficial for students to be able to equip themselves with tools and apply methodologies to perform many experiments at home rather than utilizing commercially available ECUs at exorbitant rates, thanks to the development of a low-cost ECU based on Arduino and LabVIEW in this study.

Hierarchical multi-time-scale predictive thermal management and fuel optimization for heavy-duty compression ignition engines

For heavy-duty diesel engines, NOX emissions reduction is strongly constrained by fuel efficiency. This paper presents a hierarchical model predictive controller (H-MPC) for coordinated control of tailpipe NOX emissions and fuel consumption. The H-MPC uses the separation of slow and fast dynamics that exist in the engine and its aftertreatment system. The controller is synthesized with an architecture in which a high-level MPC uses a longer prediction horizon compared to the low-level predictive controller which tracks the high-level controller command and manages the thermal dynamics of the aftertreatment system. Engine load preview enables the high-level controller to estimate the desired catalyst temperature ahead of time and addresses the selective catalytic reduction (SCR) slow thermal dynamics. Calculated by the high-level controller, the intake manifold pressure, and the start of injection (SOI) crank angle is used as reference trajectories in the low-level controller that regulates fast dynamical behaviors such as engine out NOX emissions. Hardware-in-the-loop (HIL) validation of this integrated H-MPC on a rapid prototype controller shows that when the SCR catalyst temperature is above light-off temperature (warmed-up condition), the engine operation is shifted to operate with the best fuel economy since the warmed-up SCR can efficiently reduce the engine-out NOX emissions. Results indicate that up to 0.8% benefit in cycle averaged BSFC along with a 13% reduction in tailpipe NOX compared to a stock engine calibration can be achieved with the coordinated engine and aftertreatment system through H-MPC.

Numerical Investigation of a Reactivity-Controlled Compression Ignition Engine Fueled with N-Heptane and Iso-Octane

In this numerical study, the effects of the premixed ratio, intake manifold pressure and intake air temperature on a four-cylinder, four-stroke, direct injection, low-compression-ratio gasoline engine, operated in reactivity-controlled compression ignition (RCCI) combustion mode at a constant engine speed of 1000 rpm, were investigated using Converge CFD software. The results of numerical analyses showed that the maximum in-cylinder pressure and heat release rate (HRR) increased and the combustion phase advanced depending on the rise in both intake manifold pressure and intake air temperature. The CA50 shifted by 18.5 °CA with an increment in the intake air temperature from 60 °C to 100 °C. It was observed that the combustion duration dropped from 44 °CA to 38 °CA upon boosting the intake manifold pressure from 103 kPa to 140 kPa. Moreover, a delay in the combustion phase occurred at a constant intake air temperature with an increasing premixed ratio. The maximum value of in-cylinder pressure was recorded as 36.15 bar (at 11 °CA aTDC) with the use of PRF20. Additionally, as the content of iso-octane in the fuel mixture was increased, combustion delay occurred, and the maximum value of in-cylinder temperature obtained was 11 °CA aTDC using PRF20 fuel at the earliest point. While HC and CO emissions reached the highest values at a 60 °C intake air temperature, NOx and soot emission values were detected at quite low levels at this temperature. The values of all these emissions increased with rising intake manifold pressure and reached their highest values at 140 kPa. In addition, while the highest HC and CO emission values were observed with the use of PRF60 fuel, the results revealed that the control of the combustion phase in the RCCI strategy is notably affected by the premixed ratio, intake manifold pressure and intake air temperature.

Parametric evaluation of ducted fuel injection in an optically accessible mixing-controlled compression-ignition engine with two- and four-duct assemblies

Ducted fuel injection (DFI) is a strategy to improve fuel/charge-gas mixing in direct-injection compression-ignition engines. DFI involves injecting fuel along the axis of a small tube in the combustion chamber, which promotes the formation of locally leaner mixtures in the autoignition zone relative to conventional diesel combustion. Previous work has demonstrated that DFI is effective at curtailing engine-out soot emissions across a wide range of operating conditions. This study extends previous investigations, presenting engine-out emissions and efficiency trends between ducted two-orifice and ducted four-orifice injector tip configurations. For each configuration, parameters investigated include injection pressure, injection duration, intake manifold pressure, intake manifold temperature, start of combustion timing, and intake-oxygen mole fraction. For both configurations and across all parameters, DFI reduced engine-out soot emissions compared to conventional diesel combustion, with little effect on other emissions and engine efficiency. Emissions trends for both configurations were qualitatively the same across the parameters investigated. The four-duct configuration had higher thermal efficiency and indicated-specific engine-out nitrogen oxide emissions but lower indicated-specific engine-out hydrocarbon and carbon monoxide emissions than the two-duct assembly. Both configurations achieved indicated-specific engine-out emissions for both soot and nitrogen oxides that comply with current on- and off-road heavy-duty regulations in the United States without exhaust-gas aftertreatment at an intake-oxygen mole fraction of 12%. High-speed in-cylinder imaging of natural soot luminosity shows that some conditions include a second soot-production phase late in the cycle. The probability of these late-cycle events is sensitive to both the number of ducted sprays and the operating conditions.

Dual-output PID transient control of an electric-assisted air charge system

Turbo-compressor assembly (also called turbocharger) is added to diesel engines to increase their power density and improve performance. However, during power step-up operations, the added turbocharger system could lead to a significant delay of engine response (also called turbo-lag) which negatively impact drivability. In this paper, an external electric compressor (eBoost) is added to a turbocharged, large displacement diesel engine to significantly reduce turbo-lag, along with a bypass valve. Now, the air charge system has two control targets (boost (intake manifold) pressure and rate of exhaust-gas recirculation (EGR)) but with four control actuators including EGR valve, variable geometry turbo (VGT) vane position, eBoost speed and bypass valve, making it challenge for developing the associated control scheme. In this paper, a dual-output PID (proportional-integral-derivative) controller is proposed for controlling the boost pressure using the VGT and eBoost to reduce turbo-lag, and a transition logic is also devised to detect transient operating conditions to activate the eBoost, along with the closing and opening of the bypass valve, with maximum benefit. The EGR rate PID control remains unchanged. The addition of the eBoost is shown to improve transient response time by up to 55% and reduce transient NOx emissions by up to 42% during transitional operations without negatively impacting steady-state engine performance or emissions. Note that transient performance can be further improved for production implementation when a single engine control module is used by eliminating communication delay among multiple control systems.

Knock probability determination in a turbocharged gasoline engine through exhaust gas temperature and artificial neural network

In the present study, a new combination of different available engine sensors along with an exhaust gas temperature sensor is used as the input of an artificial neural network to recognize knock incidents probability. In this regard, comprehensive experimental test trips on a turbocharged gasoline-powered vehicle are defined, and about 5 million data sets are extracted. These data are filtered, and then the optimization process is conducted on the network to minimize errors in the presented network. The output of the presented network would be the probability of knock occurrence in different operating conditions which a probability of more than 50% would be recognized as a knock occurrence. The results reveal that the neural network can detect knocking by traditional engine sensors plus exhaust gas temperature sensors with 92% precision. The exhaust gas temperature increases in most knock occurrences due to spark time retarding. The network reveals the little effect of the air temperature sensor on knock incidence, while the strong correlation of intake manifold pressure on the knock occurrence is shown. The spark timing, engine speed, intake temperature, and pressure sensor have the most considerable effect on knock detection, while the camshaft angle sensor has an almost negligible effect on knock detection. The current network promotes knock detection methods by introducing the knock probability, and additional improvement on the presented method can lead to a reliable procedure for knock detection.

Modeling and Control of Diesel Engine Emissions using Multi-layer Neural Networks and Economic Model Predictive Control

This paper presents the results of developing a multi-layer Neural Network (NN) to represent diesel engine emissions and integrating this NN into control design. Firstly, a NN is trained and validated to simultaneously predict oxides of nitrogen (NOx) and Soot using both transient and steady-state data. Based on the input-output correlation analysis, inputs to NN with the highest influence on the emissions are selected while keeping the NN structure simple. Secondly, a co-simulation framework is implemented to integrate the NN emissions model with a model of a diesel engine airpath system built in GT-Power and used to identify a low-order linear parameter-varying (LPV) model for emissions prediction. Finally, an economic supervisory model predictive controller (MPC) is developed using the LPV emissions model to adjust setpoints to an inner-loop airpath tracking MPC. Simulation results are reported illustrating the capability of the resulting controller to reduce NOx, meet the target Soot limit, and track the adjusted intake manifold pressure and exhaust gas recirculation (EGR) rate targets.

Validation and Enhancement of a Supermesh Strategy for the CFD Simulation of Four-Stroke Internal Combustion Engines

The present paper describes and validates an efficient CFD implementation to replicate the working fluid-dynamics of a real four-stroke internal combustion engine. To do this, experimental data obtained on a single-cylinder engine are used to validate the proposed computational approach. The engine domain is divided into regions according to each moving zone, and these are coupled using a pseudo-supermesh interface presented in a previous work by the authors. In this work, the original pseudo-supermesh strategy is enhanced by introducing the dual-boundary concept to model the valve opening/closing events to increase the accuracy and simplicity of the simulation procedure. The results produced by the proposed software tool show a good correlation to the experimental measurements of the complete engine cycle. Macroscopic quantities of the in-cylinder flow are accurately replicated as well as the instantaneous evolution of the in-cylinder and intake manifold pressure. Furthermore, the present work shows that the computational efficiency and scalability of the enhanced pseudo-supermesh approach are preserved even when applied to more complex real problems. In this sense, this work contributes to a new engineering tool promoting the enhanced pseudo-supermeshes as an effective tool for the design, development, and optimization of internal combustion engines.

Neural network-based air handling control for modern diesel engines

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

Investigation of the Effects of Intake Manifold Pressure on Performance and Combustion Characteristics in an HCCI Engine

Homojen dolgulu sıkıştırma ile ateşlemeli (HCCI) motorların yüksek termik verimleri ve düşük NOx emisyonları sebebiyle buji ile ateşlemeli (SI) ve sıkıştırma ile ateşlemeli (CI) motorlara göre önemli üstünlükleri bulunmaktadır. Ancak HCCI motorlarda yanma başlangıcının kontrol edilmesi oldukça zordur. Bu çalışmada, dört silindirli SI motordan dönüştürülmüş olan bir HCCI motoru kullanılmıştır. 373 K hava giriş sıcaklığı için, emme manifold basıncının HCCI yanma üzerine etkileri deneysel olarak incelenmiştir. Deney yakıtı olarak RON0, RON20 ve RON40 kullanılmıştır. Manifold basıncının artmasıyla yanma başlangıcının avansa alındığı gözlenmiştir. Ayrıca oktan sayısının değişiminin de yanma başlangıcı üzerine önemli etkileri olduğu gözlenmiştir. En yüksek indike termik verim RON40 yakıtı kullanımında, 120 kPa manifold basıncında %46,38 olarak kaydedilmiştir. Manifold basıncının artırılmasına bağlı olarak volümetrik verimin de artması maksimum silindir içi basınç ve ısı yayılımında artış sağlamıştır.

Experimental Studies of Low-Load Limit in a Stoichiometric Micro-Pilot Diesel Natural Gas Engine

While operating at light loads, diesel pilot-ignited natural gas engines with lean premixed natural gas suffer from poor combustion efficiency and high methane emissions. This work investigates the limits of low-load operation for a micro-pilot diesel natural gas engine that uses a stoichiometric mixture to enable methane and nitrogen oxide emission control. By optimizing engine hardware, operating conditions, and injection strategies, this study focused on defining the lowest achievable load while maintaining a stoichiometric equivalence ratio and with acceptable combustion stability. A multi-cylinder diesel 6.7 L engine was converted to run natural gas premix with a maximum diesel micro-pilot contribution of 10%. With a base diesel compression ratio of 17.3:1, the intake manifold pressure limit was 80 kPa(absolute). At a reduced compression ratio of 15:1, this limit increased to 85 kPa, raising the minimum stable load. Retarding the combustion phasing, typically used in spark-ignition engines to achieve lower loads, was also tested but found to be limited by degraded diesel ignition at later timings. Reducing the pilot injection pressure improved combustion stability, as did increasing pilot quantity at the cost of lower substitution ratios. The lean operation further reduced load but increased NOx and hydrocarbon emissions. At loads below the practical dual-fuel limit, a transition to lean diesel operation will likely be required with corresponding implications for the aftertreatment system.

Combined effects of electric supercharger and LP-EGR on performance of turbocharged engine

LP-EGR and turbocharging can improve thermal efficiency, but its specific mechanism needs to be further studied from the energy conversion. The fast response characteristic of electric supercharger can make up for turbine lag. The effect of electric supercharger on the steady state and transient characteristics of a LP-EGR turbocharged engine are investigated. Under the condition of 1500 r·min−1 and 14 bar, the electric supercharger can increase the EGR rate from 5% to 30%. The introduction of exhaust gas can increase the intake volume and reduce the pumping losses. The increase of turbocharger power indicates the reduction of exhaust energy losses. The decrease of combustion temperature optimizes the combustion phase, increases the constant volume degree of combustion and reduces the heat transfer losses. The application of EGR improves the fuel economy by 5%. For emission, low temperature combustion and low oxygen content reduce NOx emission by 80%. Incomplete combustion losses increase THC emission. CO emission is related to excess-air coefficient, so it is basically unchanged. The electric supercharger can speed up the establishment of the intake manifold pressure. The power transient response time is shortened by 72%. The advance of torque platform improves the power performance of engine at low speed.

Benefits of Feedforward for Model Predictive Airpath Control of Diesel Engines

This paper investigates options to complement a diesel engine airpath feedback controller with a feedforward. The control objective is to track the intake manifold pressure and exhaust gas recirculation (EGR) rate targets by manipulating the EGR valve and variable geometry turbine (VGT) while satisfying state and input constraints. The feedback controller is based on rate-based Model Predictive Control (MPC) that provides integral action for tracking. Two options for the feedforward are considered one based on a look-up table that specifies the feedforward as a function of engine speed and fuel injection rate, and another one based on a (non-rate-based) MPC that generates dynamic feedforward trajectories. The controllers are designed and verified using a high-fidelity engine model in GT-Power and exploit a low-order rate-based linear parameter-varying (LPV) model for prediction which is identified from transient response data generated by the GT-Power model. It is shown that the combination of feedforward and feedback MPC has the potential to improve the performance and robustness of the control design. In particular, the feedback MPC without feedforward can lose stability at low engine speeds, while MPC-based feedforward results in the best transient response. Mechanisms by which feedforward is able to assist in stabilization and improve performance are discussed.

Extreme Miller cycle with high intake boost for improved efficiency and emissions in heavy-duty diesel engines

This study experimentally investigates the impact of extreme Miller cycle strategies paired with high intake manifold pressures on the combustion process, emissions, and thermal efficiency of heavy-duty diesel engines. Well-controlled experiments isolating the effect of Miller cycle strategies on the combustion process were conducted at constant engine speed and load (1160 rpm, 1.76 MPa net IMEP) on a single cylinder research engine equipped with a fully-flexible hydraulic valve train system. Late intake valve closing (LIVC) timing strategies were compared to a conventional intake valve profile under either constant cylinder composition, constant engine-out NOx emission, or constant overall turbocharger efficiency ([Formula: see text]) to investigate the operating constraints that favor Miller cycle operation over the baseline strategy. Utilizing high boost with conventional intake valve closing timing resulted in improved fuel consumption at the expense of sharp increases in peak cylinder pressures, engine-out NOx emissions, and reduced exhaust temperatures. Miller cycle without EGR at constant [Formula: see text] demonstrated LIVC strategies effectively reduce engine-out NOx emissions by up to 35%. However, Miller cycle associated with very aggressive LIVC timings led to fuel consumption penalties due to increased pumping work and exhaust enthalpy. LIVC strategies allowed for increased charge dilution at the baseline NOx constraint of 3.2 g/kWh, resulting in significant fuel consumption benefits over the baseline case without compromising exhaust temperatures or peak cylinder pressures. As Miller cycle implementation was shown to affect the boundary conditions dictating [Formula: see text], the LIVC and conventional IVC cases were studied at an equivalent [Formula: see text] point representative of high boost operation. With high boost, LIVC yielded reduced NOx emissions, reduced peak cylinder pressures, and elevated exhaust temperatures compared to the conventional IVC case without compromising fuel consumption.