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Efficient and robust control strategies can greatly contribute to the reliability of fuel cell systems, and a stable output voltage is a key criterion for evaluating a fuel cell system's reliability as a power source. In this study, a polymer electrolyte fuel cell (PEFC) system model is developed, and its performances under different operating conditions are studied. Then two different novel controllers—a proportional integral derivative (PID) controller and a model predictive control (MPC) controller—are proposed and applied in the PEFC system to control its output voltage at a desired value by regulating the hydrogen and air flow rates at the same time, which features a multi-input and single-output control problem. Simulation results demonstrate that the developed PEFC system model is qualified to capture the system's behavior. And both the developed PID and MPC controllers are effective at controlling the PEFC system's output voltage. While the MPC controller presents superior performance with faster response and smaller overshoot. The proposed MPC controller can be easily employed in various control applications for fuel cell systems.

Flex-fuel engines can operate on different fuels, from fossil fuel to renewable fuel and their mixture. With the assumption that fuel species is unknown in advance, the mutative fuel properties give rise to an interesting control problem. Since the combustion phasing and ignition delay in the combustion process are intimately coupled, the fuel injection system and air system need to be combined for performance. In this work, an adaptive Model Predictive Control (MPC) approach is proposed to control the combustion process in a multi-cylinder heavy duty compression-ignition (CI) engine. MPC is a suitable design for this multiple inputs/outputs system with actuator constraints, and adaptivity is the solvent for the unknown mutative fuel properties. The combustion timing and ignition delay are extracted from cooled in-cylinder pressure sensors and simultaneously controlled by manipulating injection timings, the intake oxygen concentration, and intake pressure using an exhaust-gas recirculation (EGR) system and a variable-geometry turbocharger (VGT). Diesel, gasoline/n-heptane mixture, and ethanol/n-heptane mixture are used in the experiments. The method is validated in fuel transitions from diesel to gasoline mixture and from gasoline mixture to ethanol mixture.

[EN] This work evaluates the performance and emissions of the series hybrid vehicle concept powered by a gasoline partially premixed internal combustion engine. To do so, experimental data was collected from a Volvo VED-D4 Euro 6 four-cylinder compression ignition engine running under gasoline partially premixed combustion. Two series hybrid vehicle models were developed in GT-Power (R), which were fed with the experimental data to evaluate the potential of the hybrid concept. First of all, the battery charging strategy of the hybrid vehicles was optimized in terms of number of power levels and operating conditions. For this, a design of experiments was performed in GT-Power (R), which enabled to obtain a predictive model of the performance and emissions. The predictive model was used to obtain the optimized NOx-fuel consumption Pareto frontiers for each charging strategy proposed. Finally, the GT-Power (R) vehicle models were run with the optimal operating conditions (selected from each Pareto) in both the new European driving cycle and worldwide harmonized light vehicles test cycle. The results show that the hybrid powertrain running with partially premixed combustion is able to achieve similar or better performance than the commercial diesel vehicle with low engine-out emissions. Moreover, comparing the results from both vehicles, it was confirmed that the hybridization results in better improvements when applied to urban traffic than for highway conditions where the power request is higher and the potential for regenerative braking is reduced., The authors gratefully acknowledge FEDER and Spanish Ministerio de Economia y Competitividad for partially supporting this research through TRANCO project (TRA2017-87694-R). The authors also gratefully acknowledge the KCFP Engine Research Center (Swedish Energy Agency grant number 22485-4) for partial support of this research.

Modern transportation requires advanced powertrain systems to reduce the production of greenhouse gas CO2. Partially premixed combustion (PPC) is one of the most promising methods to achieve low emission and low fuel consumption of internal combustion engines. The present paper evaluated the effects of the calibration parameters on the efficiency and emissions of a multi-cylinder engine using PPC during stable operations, and the performance of the engine during transient operations. The peak gross indicated efficiency of 51.5% and the peak net indicated efficiency of 48.7% were achieved under stable operating conditions. The transient results also demonstrate an average net indicated efficiency of 47.5%. The nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbon (HC) conform with the Euro VI emission legislation in the case of most transient operations except some low load points.

Improving the efficiency of the powertrain system is of great importance to reduce the greenhouse gas CO2. Advanced combustion engine with Partially Premixed Combustion (PPC) is one of the best solutions. It is proved to have a high engine efficiency and low emission level. Using multiple injections is a good way to achieve PPC. The efficiencies using multiple injections were evaluated on a metal engine with modern architecture and the reasoning behind that was explored on an optical engine. The metal engine results shown that the point with optimized multiple injections is of higher efficiency than a single injection. Optical results demonstrated that the direct interaction of the first and later injection, as well as the interactions of the fuel and the in-cylinder bulk flow fields and surfaces, could affect mixing and fuel movement and, hence the efficiency. One of the reasons why the optimized multiple injections have a higher efficiency is that the center of the fuel is moved close to the center of the cylinder. Thus, the heat transfer between the heat produced from the fuel-gas mixture and the cylinder liner can be reduced by the isolation. This explains how the injections influence the fuel distribution and the heat transfer and, hence, the engine efficiency.

Partially premixed combustion with low octane fuel aims to reduce NOx and soot emission simultaneously without fuel consumption penalty. Cylinder pressure based combustion phase control is an essential technology for partially premixed combustion. A novel closed-loop combustion phase control strategy for multiple combustion modes is proposed in the current study. The combustion modes are classified into three basic categories based on injection patterns and heat release stages: (1) with only one heat release stage; (2) with two separated heat release stages; (3) with two overlapped heat release stages. Crank angle when 50% fuel is consumed (CA50) is chosen as the combustion phase indicator for the first case. Start of combustion (SOC) of each heat release stage is the combustion phase indicator for the second case. Both SOC and CA50 are the combustion phase indicators for the third case. Each combustion phase is closed-loop controlled by a proportional–integral (PI) controller with the timing adjustments of the corresponding injection. The control strategy is verified under different operating conditions in a 1.9 L light duty diesel engine fueled by gasoline-diesel mixture (volumetric 70% gasoline, 30% diesel). The experimental results show that the control strategy is able to control the combustion phase, reduce cylinder to cylinder variations as well as cycle to cycle variations under the operating conditions with exhaust gas circulation (EGR) rates of 10% and 15%.

Recent outlooks suggest a long-term relevance of internal combustion engines for both power generation and transportation. Nonetheless, stringent pollutant reduction requirements combined with new CO2 mandates draws a challenging scenario, requiring intensive research and development activities to develop and optimize combustion modes to fulfill these requirements. Among the recent advancements, the active pre-chamber ignition system has been considered as a potential alternative to achieve a highly efficient and clean combustion process. Its combustion development is dictated by the pre-chamber ignition system which will provides a high energy flow jet inside the main chamber to enable a multi-site oxidation of the global lean mixture. The comprehension and quantification of the flow and combustion characteristics of the pre-chamber are of utmost importance to optimize the engine operation and pre-chamber design. Nonetheless, restrictive space for instrumentation at experimental side requires alternative numerical methods to aid the quantification of the state parameters and combustion process of these systems. In this sense, this research proposes a novel methodology combining in-cylinder pressure measurement and 1-D simulations as a tool to determine the state, flow and combustion development of different active pre-chambers operating with natural gas in a heavy-duty engine for power generation. The methodology is developed considering 3 different pre-chamber geometries, operating at different spark timings and equivalence ratios. The results suggest that the methodology is able to quantify the state conditions prior to the spark discharge as well as the evolution of the combustion process by means of considering the perturbations of the mass flow from the pre-chamber inside the main chamber energy balance. Moreover, the methodology allowed to quantify variations of equivalence ratio as small as 0.1 and combustion durations variations of 1 CAD.

This study investigates particulate matter (PM) and regulated emissions from renewable rapeseed oil methyl ester (RME) biodiesel in pure and blended forms and contrasts that to conventional diesel fuel. Environmental and health concerns are the major motivation for combustion engines research, especially finding sustainable alternatives to fossil fuels and reducing diesel PM emissions. Fatty acid methyl esters (FAME), including RME, are renewable fuels commonly used from low level blends with diesel to full substitution. They strongly reduce the net carbon dioxide emissions. It is largely unknown how the emissions and characteristics of PM get altered by the combined effect of adding biodiesel to diesel and implementing modern engine concepts that reduce nitrogen oxides (NOx) emissions by exhaust gas recirculation (EGR). Therefore, the exhaust from a single-cylinder Scania D13 heavy-duty (HD) diesel engine fuelled with petroleum-based MK1 diesel, RME, and a 20% RME blend (B20), was sampled while the inlet oxygen concentration was stepped from ambient to very low by varying EGR. Regulated gaseous emissions, mass of total black carbon (BC) and organic aerosol (OA), particle size distributions and the soot nanostructure by means of transmission electron microscopy (TEM), were studied. For all EGR levels, RME showed reduced BC emissions (factor 2 for low and 3-4 for higher EGR) and total particulate number count (TPNC) compared with diesel and B20. B20 was closer to diesel than RME in emission levels. RME opens a significant possibility to utilise higher levels of EGR and stay in the region of low NOx, while not producing more soot than with diesel and B20. Adding EGR to 15% inlet O2 did not affect the nanostructure of PM. A difference between the fuels was noticeable: Branched agglomerates of diesel and RME were composed of many primary particles, whereas those of B20 were more often "melted" together (necking).

Transient mixing and ignition mechanisms in a simplified pre-chamber/main-chamber system are investigated using direct numerical simulation (DNS) with detailed chemical kinetics. Full ignition and flame propagation processes in the premixed methane/air mixtures are simulated. Ignition, the progress and topology of flame evolution, and the mean burning velocity in the main chamber are analyzed in detail. Four important phases in the ignition and flame propagation processes are identified based on the flame structure development in the main chamber, the pressure and velocity evolution at typical points in both the pre-chamber and main chamber. Results show that the intermediate species OH, CH2O, and HO2 are critical for flame stabilization and propagation in the main chamber due to their high reactivity. This is sorted as the chemical effect that the pre-chamber jet acts on the main chamber. The high temperature jet also brings heat and unburned fuel into the main chamber, which are sorted as thermal and enrichment effect, respectively. The heat release rate is found to be approximately proportional to the product of CH2O and OH mass fractions, which could be regarded as a reliable and effective marker for the heat release rate of methane/air mixtures. It is found that the mean burning velocity in the main chamber can be elevated up to 30 times under the condition investigated.

Gasoline-fueled Partially Premixed Combustion is an advanced combustion concept approaching high efficiency as well as low emissions. The most challenging task on controlling a gasoline PPC engine is to regulate the maximum pressure rise rate to reduce engine noise and durability problem. A trade-off relationship between pressure rise rate and soot emissions is observed as a function of pilot injection event. In this paper, a control-oriented model is developed to predict in-cylinder pressure and engine outputs through fuel injection events. Thereafter, two controllers structured with PI and MPC are designed and evaluated separately. Simulation results show that, both controllers satisfy the objective of achieving desired engine load and combustion phasing, with the constraints of pressure rise rate and soot emissions simultaneously. MPC controller produces a smoother transient move with less overshoot, comparing with PI controller with a fast response.

Partially premixed combustion (PPC) is a hybrid combustion of Homogeneous Charge Compression Ignition (HCCI) and Diesel Combustion (DC), which has a great potential in reducing the fuel consumption. PPC has a longer premixed time than DC but lesser than HCCI. Therefore it is more stratified than HCCI. This paper first presents results on how the stratification using multiple injections and different EGR influence the efficiency and proposes a control framework for PPC stratification control inspired from the experiments. The control framework is validated in transient operations. Results in both steady and transient operations demonstrated that the more stratified PPC with multiple injections has a lower fuel consumption.

Sliding mode control (SMC) is to keep the system to a stable differential manifold. Model predictive control (MPC) calculates the control input by solving an optimization problem on receding horizon. The method of receding horizon sliding control (RHSC) includes the predicted information into the SMC design by combining SMC and MPC. Considering the modeling error and measurement noise, there are model-mismatch and disturbance problems in control practice. This paper combines the demonstrated method of RHSC with a state-augmented Kalman filter addressing the model mismatch and disturbance problem. The proposed scheme has been applied to the air system of an advanced heavy-duty engine. The results have shown the capability of tracking the reference signal during a step-response test and the convergence rate to the target signal is 10% faster than MPC.

Low temperature combustion (LTC) of high-octane number fuels in compression ignition engines offers an opportunity to simultaneously achieve high engine thermal efficiency and low emissions of NO x and particulate matter without using expensive after-treatment technologies. LTC engines are known to be sensitive to the operation conditions and combustor geometry. It is important to understand the fundamental flow and combustion physics in order to develop the technology further for commercial application. A joint numerical and experimental investigation was conducted in a heavy-duty compression ignition engine using a primary reference fuel with an octane number of 81 to investigate the effects of injection timing, piston geometry, and compression ratio (CR) on the fuel/air mixing and combustion covering different regimes of LTC engines, homogeneous charge compression ignition (HCCI), partially premixed combustion (PPC), and the transition regime from HCCI to PPC. The results show that with the same combustion timing, a higher CR leads to a lower NO x , but a higher emission of UHC and CO. The piston geometry shows a significant impact on the combustion and emission process in the transition regime while it has minor influence in the HCCI and PPC regimes. It is found that high engine efficiency and low emissions of NO x , CO and UHC can be achieved in the earlier PPC regime and later transition regime. The fundamental reason behind this is the stratification of the mixture in composition, temperature and reactivity, which is dictated by the interaction between the spray and the cylinder/piston walls.

Partially Premixed combustion (PPC) is a promising combustion concept to achieve high engine efficiency. The combustion-timing of PPC is affected by both inlet-charge condition and the fuel injection, a simple map-based feed-forward control method is not sufficient for controlling the combustion during transient operation. This paper investigates a model-based control method to solve this control problem. A non-linear model was developed to capture the main trend of inlet-gas condition and injection. A Model Predictive Controller (MPC) was designed to control injection timing and the gas-exchange system. The controller was verified in a multi-cylinder heavy-duty PPC engine.

Modelica allows systems to be described with reuseable components and with a high precision. To be able to use such complex models efficiently, high demands are set on tools that allow the user to extract the information needed from the models in a straight-forward manner. For this purpose, design-of-experiments techniques can be used to systematically analyze the complex models.In this paper, it is demonstrated how a Modelica model of a diesel engine can be used for control design. The engine model has multiple inputs and outputs, it is nonlinear, has many parameters, and has a higher order than most control design algorithms are able to handle in a numerically robust way.It is shown how the features for dynamic design-of-experiments analysis in the FMI Toolbox for MATLAB can be used to analyze the variation in system dynamics across the engine operating range. A gain scheduling of nine multivariable linear-quadratic-gaussian (LQG) controllers, is designed based on linearization and model reduction of the original nonlinear FMU model. (Less)

We hope this special issue will provide new inspiring to the community of control theory, especially for the youngerresearchers and students. We wish to thank Yiguang Hong, Editor of the journal of ...

[EN] Recent emission legislation in the marine sector has emphasized the need to reduce nitrogen oxides (NOx) emissions as well as sulphur emissions. The fulfilment of emission legislation limits with conventional marine diesel oil (MDO) requires complex and expensive aftertreatment systems and in this framework lean burn pilot ignited dual fuel (diesel and natural gas) is revealed as one of the most suitable engine platforms to decrease pollutant formations at its source and therefore to mitigate aftertreatment system requirements. For this reason, an experimental study has been carried out in an 8.8 l dual fuel single cylinder Wartsila 20DF engine in order to evaluate different diesel equivalence ratio distributions in the combustion chamber and to get a deeper insight into the interaction between the high reactivity (diesel) and the low reactivity (natural gas) fuels during the ignition process. Engine testing has been complemented with diesel spray pattern simulations for a better understanding of local combustion conditions. Results show the importance of local pilot fuel distribution as a way to control combustion phasing and consequently its impact on combustion instability, emissions and knock conditions. Stable combustion with engine-out NOx levels below legislation have been achieved without the need of after-treatment system using appropriate high reactivity fuel (HRF) distribution control. (C) 2017 Elsevier Ltd. All rights reserved., Special thanks to all technicians of the Division of Combustion Engines at Lund University involved in the project. Financial support from The KCFP Engine Research Center is graciously acknowledged by the authors. The authors acknowledge Wartsila Corporation for supporting this research and providing the test engine. The author J. Monsalve-Serrano acknowledges the financial support from the Universitat Politecnica de Valencia under the grant Ayudas Para la Contratacion de Doctores para el Acceso al Sistema Espanol de Ciencia, Tecnologia e Innovacion.

Finding the correct Top Dead Center (TDC) offset for an internal combustion engine is harder than it seems. This study introduces a novel method to find the TDC offset based on the simple assumption that the heat loss power through the combustion chamber walls is constant for motored cycles in a narrow Crank Angle interval around TDC. The proposed method uses nonlinear least squares optimization to find the combination of specific heat ratio and TDC offset that makes the heat loss power as constant as possible. An important subproblem is to determine the peak pressure location with high accuracy. Fitting a third order Fourier series to the motored cylinder pressure allows the pressure maximum to be estimated with a standard deviation of 0.005° Crank Angle (CA) and it can also be used instead of the measured pressure to reduce the uncertainty of the TDC estimate by approximately 50%. The standard deviation of a single-cycle TDC estimate is approximately 0.025° CA when using a crank resolution of 0.2° CA for the measurements. The bias of the TDC estimate is in the 0-0.02° CA range both when comparing to measurements with a TDC sensor and with simulated motored cycles. The method can be used both for calibration and on-board diagnostics purposes e.g. during cranking, fuel cut-off or engine switch-off. The third order Fourier series fit comes with a significant computational penalty but since it is only applied very intermittently this does not have to be a serious issue.

The paper describes a novel method for self-tuning gross heat release computation in internal combustion engines suitable for both online usage in combustion phasing control applications and post-processing of cylinder pressure measurements. The method estimates the polytropic exponents and cylinder pressure offsets immediately preceding and succeeding the combustion event, respectively, using a fast nonlinear least-squares method. The polytropic exponent and the pressure offset are subsequently interpolated during the combustion event and a net heat release computation is performed based on the interpolated exponent and pressure. The result is a self-tuning gross heat release algorithm with no need to model heat losses, crevice losses and blow-by explicitly. (C) 2008 Elsevier Ltd. All rights reserved. (Less)

Finding the correct top dead center (TDC) offset for an internal combustion engine is harder than it seems. This paper introduces a novel method to find the TDC offset based on a simple assumption that the heat loss power through the combustion chamber walls is constant for motored cycles in a narrow crank angle interval around TDC. The proposed method uses nonlinear least squares optimization to find the combination of specific heat ratio and TDC offset that makes the heat loss power as constant as possible. The standard deviation of the TDC estimate is approximately 0.05° crank angle (CA) when using a crank resolution of 0.2°CA for the measurements. The bias of the TDC estimate is in the 0–0.02°CA range both when comparing to measurements with a TDC sensor and with simulated motored cycles. The method can be used both for calibration and on-board diagnostics purposes e.g. during cranking, fuel cut-off or engine switch-off.

An estimation model which uses the net heat release profile for estimating the cylinder air/fuel ratio of a spark ignition engine is developed. The net heat release profile is computed from the cylinder pressure trace and quantifies the conversion of chemical energy of the reactants in the charge into thermal energy. The net heat release profile does not take heat- or mass transfer into account. Cycle-averaged air/fuel ratio estimates over a range of engine speeds and loads show an RMS error of 4.1% compared to measurements in the exhaust.

In this paper a method for control of air–fuel ratio (AFR) in cold or lean-burning spark-ignited engines is investigated. The technique uses combustion pressure as measured by a cylinder-mounted sensor, and is based on the phenomenon of increasing cycle-to-cycle combustion pressure variation as the air–fuel mixture approaches the limits of flammability. The cylinder pressure is measured from one engine cycle to the next, and large drops in mean effective pressure (IMEP) are used as an indicator of poor combustion. In response, the airflow or fuel flow to the engine can be manipulated. In a series of experiments, the air and fuel are alternately investigated as control inputs, and performance compared. The resulting control system is a high-bandwidth AFR control strategy that can be used under cold or lean conditions when conventional exhaust gas oxygen sensor cannot be used. Moreover, the method is directly tied to the combustion process and the relevant performance measure — combustion stability — that is perceptible to the driver as a rough-running engine.

Partially premixed combustion (PPC) is a low temperature, direct-injection combustion concept that has shown to give promising emission levels and efficiencies over a wide operating range. In this concept, high EGR ratios, high octane-number fuels and early injection timings are used to slow down the auto-ignition reactions and to enhance the fuel and are mixing before the start of combustion. A drawback with this concept is the combustion stability in the low-load region where a high octane-number fuel might cause misfire and low combustion efficiency. This paper investigates the problem of low-load PPC controller design for increased engine efficiency. First, low-load PPC data, obtained from a multi-cylinder heavy- duty engine is presented. The data shows that combustion efficiency could be increased by using a pilot injection and that there is a non-linearity in the relation between injection and combustion timing. Furthermore, intake conditions should be set in order to avoid operating points with unfavourable global equivalence ratio and in-cylinder temperature combinations. Model predictive control simulations were used together with a calibrated engine model to find a gas-system controller that fulfilled this task. The findings are then summarized in a suggested engine controller design. Finally, an experimental performance evaluation of the suggested controller is presented.

Cylinder pressure sensors provide detailed information on the diesel engine combustion process. This paper presents a method to use cylinder-pressure data for prediction of engine emissions by exploiting data-mining techniques. The proposed method uses principal component analysis to reduce the dimension of the cylinder-pressure data, and a neural network to model the nonlinear relationship between the cylinder pressure and emissions. An algorithm is presented for training the neural network to predict cylinder-individual emissions even though the training data only provides cylinder-averaged target data. The algorithm was applied to an experimental data set from a six-cylinder heavy-duty engine, and it is verified that trends in emissions during transient engine operation are captured successfully by the model.

Stoichiometric operation of Spark Ignited (SI) Heavy Duty Natural Gas (HDNG) engines with a three way catalyst results in very low emissions however they suffer from bad gas-exchange efficiency due to use of throttle which results in high throttling losses. Variable Geometry Turbine (VGT) is a good practice to reduce throttling losses in a certain operating region of the engine. VTG technology is extensively used in diesel engines; it is very much ignored in gasoline engines however it is possible and advantageous to be used on HDNG engine due to their relatively low exhaust gas temperature. Exhaust gas temperatures in HDNG engines are low enough (lower than 760 degree Celsius) and tolerable for VGT material. Traditionally HDNG are equipped with a turbocharger with waste-gate but it is easy and simple to replace the by-pass turbocharger with a well-matched VGT. By altering the geometry of the turbine housing, the area for exhaust gases can be adjusted and results in the desired torque. Because of this the turbo lag is very low and it has a low boost threshold. Low boost threshold means that VGT can cover a big operation range of the engine from low engine speeds to high. In this operation range the throttle can be fully open and VGT is used instead of the throttle to control the desired torque which results in eliminating the throttling losses. This paper presents experimental results which show the feasibility of reducing throttling losses by means of VGT. The operating region which is appropriate for controlling the desired torque by VGT instead of throttle is specified. The gains in terms of gas exchange efficiency are quantified. Furthermore the dynamics of using VGT is quantified and compared with throttle. The experiments were performed successfully and the results showed at least 2 unit percent improvement in gas-exchange efficiency. A comparable dynamic to throttle is observed.

When simulating homogenous charge compression ignition or HCCI using one-dimensional models it is important to have the right combustion parameters. When operating in HCCI the heat release parameters will have a high influence on the simulation result due to the rapid combustion rate, especially if the engine is turbocharged. In this paper an extensive testing data base is used for showing the combustion data from a turbocharged engine operating in HCCI mode. The experimental data cover a wide range, which span from 1000 rpm to 3000 rpm and engine loads between 100 kPa up to over 600 kPa indicated mean effective pressure in this engine speed range. The combustion data presented are: used combustion timing, combustion duration and heat release rate. The combustion timing follows the load and a trend line is presented that is used for engine simulation. The combustion duration in time is fairly constant at different load and engine speeds for the chosen combustion timings here. The heat release rate is fitted to a Wiebe function where the heat release parameter m is found. It is shown that this parameter m scale to the load and the presented trend line is used for simulating the heat release. When the engine is operated with negative valve overlap the mass flow is reduced through the engine. In an engine simulation the valve timings has to be estimated for different intake temperatures and boost pressure levels. By using the intake temperature at intake valve closing as a prediction tool for the temperature at top dead center, the exhaust valve closing timing can be estimated and will then follow the real test results closely as shown in a GT-Power simulation. The turbocharged test engine is an in-line four cylinder gasoline engine with a total displacement of 2.2 l. The engine is direct injected of spray-guided type. To achieve HCCI combustion the engine is operated with low lift and short duration valve timings where the variable negative valve overlap is used for combustion control. (Less)

High EGR rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy duty spark ignition Natural Gas engines. With stoichiometric conditions a three way catalyst can be used which means that regulated emissions can be kept at very low levels. Most of the heavy duty NG engines are diesel engines which are converted for SI operation. These engine’s components are in common with the diesel-engine which put limits on higher exhaust gas temperature. The engines have lower maximum load level than the corresponding diesel engines. This is mainly due to the lower density of NG, lower compression ratio and limits on knocking and also high exhaust gas temperature. They also have lower efficiency due to mainly the lower compression ratio and the throttling losses. However performing some modifications on the engines such as redesigning the engine’s piston in a way to achieve higher compression ratio and more turbulence, modifying EGR system and optimizing the turbocharging system will result in improving the overall efficiency and the maximum load limit of the engine. This paper presents the detailed information about the engine modifications which result in improving the overall efficiency and extending the maximum load of the engine. Control-related problems associated with the higher loads are also identified and appropriate solutions are suggested.

This paper presents experimental results on model predictive control of the combustion phasing in a Homogeneous Charge Compression Ignition (HCCI) engine. The controllers were based on linearizations of a previously presented physical model of HCCI including cylinder wall temperature dynamics. The control signals were the inlet air temperature and the inlet valve closing. A system for fast thermal management was installed and controlled using mid-ranging control. The resulting control performance was experimentally evaluated in terms of response time and steady-state output variance. For a given operating point, a comparable decrease in steady-state output variance was obtained either by introducing a disturban ce model or by changing linearization point. The robustness towards disturbances was investigated as well as the effects of varying the prediction and control horizons.

In the study presented in this paper, experimental data from a pneumatic hybrid has been compared to the results from a simulation of the engine in GT-Power. The engine in question is a single-cylinder Scania D12 diesel engine, which has been converted to work as a pneumatic hybrid. The base engine model, provided by Scania, is made in GT-Power and it is based on the same engine configuration as the one used during real engine testing. During pneumatic hybrid operation the engine can be used as a 2-stroke compressor for generation of compressed air during vehicle deceleration and during vehicle acceleration the engine can be operated as a 2-stroke air-motor driven by the previously stored pressurized air. There is also a possibility to use the stored pressurized air in order to supercharge the engine when there is a need for high torque, like for instance at take off after a standstill or during an overtake maneuver. Previous experimental studies have shown that the pneumatic hybrid is a promising concept and a possible competitor to the electric hybrid. This paper consists mainly of two parts. The first one describes an attempt to recreate the real engine as a computer model with the aid of the engine simulation software GT-power. A model has been created and the results have been validated against real engine data. The second part describes a parametric study where different parameters and their effect on pneumatic hybrid performance have been investigated.

Homogenous charge compression ignition (HCCI) has been identified as a promising way to increase the efficiency of the spark-ignited engine, while maintaining low emissions. The challenge with HCCI combustion is excessive pressure rise rate, quantified here with Ringing Intensity. Turbocharging enables increased dilution of the charge and thus a reduction of the Ringing Intensity. The engine used is an SI four cylinder base with 2.2\emph{L} displacement and is equipped with a turbocharger. Combustion phasing control is achieved with individual intake/ exhaust cam phasing. Fuel injection with spray guided design is used. Cycle resolved combustion state is monitored and used for controlling the engine either in closed or open loop where balancing of cylinder to cylinder variations has to be done to run the engine at high HCCI load. When load is increased the NOx levels rise, the engine is then run in stoichiometric HCCI mode to be able to use a simple three-way catalyst. The fuel used is 95 RON pump gasoline and injection strategies are evaluated in order to maintain low soot levels and high efficiency. Limitations and benefits on operating range are examined between 1000 and 3000 rpm. This paper investigates how to extend the HCCI range and how to reduce the high pressure rise rate with: increased boost from turbocharging, external EGR and different injection strategies. A higher boost pressure was found to extend the load range. It is shown that the limitation from high RI, NOx or soot is not the same in all engine speed and load points. By turbocharging the engine in HCCI mode there is greater flexibility to increase the range of practical operating points. (Less)

The operating range in HCCI mode is limited by the excessive pressure rise rate and therefore high combustion induced noise. The HCCI range can be extended with turbocharging which enables increased dilution of the charge and thus a reduction of combustion noise. When the engine is turbocharged the intake charge will have a high temperature at increased boost pressure and can then be regulated in a cooling circuit. Limitations and benefits are examed at 2250 rpm and 400 kPa indicated mean effective pressure. It is shown that combustion stability, combustion noise and engine efficiency have to be balanced since they have optimums at different intake temperatures and combustion timings. The span for combustion timings with high combustion stability is narrower at some intake temperatures and the usage of external EGR can improve the combustion stability. It is found that the standard deviation of combustion timing is a useful tool for evaluating cycle to cycle variations. One of the benefits with HCCI is the low pumping losses, but when load and boost pressure is increased there is an increase in pumping losses when using negative valve overlap. The pumping losses can then be circumvented to some extent with a low intake temperature or EGR, leading to more beneficial valve timings at high load.

Fuel economy and emissions are the two central parameters in heavy duty engines. High EGR rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy duty spark ignition engines. With stoichiometric conditions a three way catalyst can be used which keeps the regulated emissions at very low levels. The Lambda window which results in very low emissions is very narrow. This issue is more complex with transient operation resulting in losing brake efficiency and also catalyst converting efficiency. This paper presents different control strategies to maximize the reliability for maintaining efficiency and emissions levels under transient conditions. Different controllers are developed and tested successfully on a heavy duty 6-cylinder port injected natural gas engine. Model Predictive Control (MPC) was used to control lambda which was modeled using System Identification. Furthermore, a Proportional Integral (PI) regulator combined with a feedforward map for obtaining Maximum Brake Torque (MBT) timing was applied. The results show that excellent steady-state and transient performance can be achieved.

High EGR rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy-duty spark ignition engines. With stoichiometric conditions a three-way catalyst can be used which means that regulated emissions can be kept at very low levels. Obtaining reliable spark ignition is difficult however with high pressure and dilution. There will be a limit to the amount of EGR that can be tolerated for each operating point. Open-loop operation based on steady state maps is difficult since there is substantial dynamics both from the turbocharger and from the wall heat interaction. The proposed approach applies standard closed-loop lambda control for controlling the overall air/fuel ratio for a heavy-duty, 6-cylinder, port-injected natural gas engine. A closed-loop load control is also applied for keeping the load at a constant level when using EGR. Furthermore, cylinder pressure-based dilution limit control is applied on the EGR in order to keep the coefficient of variation at the desired level of 5%. This way confirms that the EGR ratio is kept at its maximum stable level all times. Pumping losses decrease due to the further opening of the throttle, thereby the gas exchange efficiency improves and since the regulator keeps track of the changes the engine all the time operates in a stable region. Our findings show that excellent steady-state performance can be achieved using closed-loop combustion control for keeping the EGR level at the highest level while the stability level is still good enough. (Less)

This paper offers a two-zone, physical, NOx model with low computational cost, implemented in C on an embedded system. The model is able to compute NOx-emission formation with high time resolution during an engine cycle. To do this the model takes cylinder pressure and injected fuel amount as inputs and produces NO concentration as output. The model as such is not new, nevertheless the physical background of the model as well as the equations upon which the model is based had to be briefly described to facilitate the understanding of the subsequent work. The main part of the paper is devoted to the process of developing an algorithm implementing the described model, techniques used and issues encountered are described. The resulting algorithm was implemented in C and tested on an embedded ARM processor. For the sake of implementation, parts of the algorithm had to be pre-computed and stored in tables, allowing significant acceleration of the computations. Since the model is non-linear, exponentially spaced tables had to be developed in order to successfully tabulate the parts needed without consuming too much memory. Much of the methods presented are also applicable in a variety other applications when it is desirable to implement fast versions of complex algorithms and models. The outcome regarding computation speed and memory needed is discussed. The final result is a low-cost NOx model, which is able to compute several orders of magnitude faster than NOx models known so far, implemented in C on an embedded system.

The Homogeneous Charge Compression Ignition (HCCI) principle holds promise to increase efficiency and to reduce emissions from internal combustion engines. As HCCI combustion lacks direct ignition timing control and auto-ignition depends on the operating condition, control of auto-ignition is necessary. Since auto-ignition of a homogeneous mixture is very sensitive to operating conditions, a fast combustion phasing control is necessary for reliable operation. To this purpose, HCCI modeling and model-based control with experimental validation were studied. A six-cylinder heavy-duty HCCI engine was controlled on a cycle-to-cycle basis in real time by applying in-cylinder pressure feedback. A low-complexity physical model was developed, aiming at describing the major thermodynamic and chemical interactions in the course of an engine stroke. The model shows the importance of thermal interaction between the combustion and the cylinder walls. The model was used to synthesize a controller for controlling the combustion phasing by varying the inlet valve closing and the inlet temperature. The sythesized controller behaves well both in steady-state and during step changes of the desired combustion phasing.

High EGR rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy-duty spark ignition engines. With stoichiometric conditions a three-way catalyst can be used which means that regulated emissions can be kept at very low levels. Obtaining reliable spark ignition is difficult however with high pressure and dilution. There will be a limit to the amount of EGR that can be tolerated for each operating point. Open-loop operation based on steady state maps is difficult since there is substantial dynamics both from the turbocharger and from the wall heat interaction. The proposed approach applies standard closed-loop lambda control for controlling the overall air/fuel ratio. Furthermore, ion-current-based dilution limit control is applied on the EGR in order to maximize EGR rate as long as combustion stability is preserved. The proposed control strategy has been successfully tested on a heavy-duty, 6-cylinder, port-injected natural gas engine and our findings show that 1.5-2.5% units (depending on the operating points) improvement in Brake Efficiency can be achieved. (Less)

In the study presented in this paper a single-cylinder Scania D12 diesel engine has been converted to work as a pneumatic hybrid. During pneumatic hybrid operation, the engine can be used as a 2-stroke compressor for generation of compressed air during vehicle deceleration and during vehicle acceleration the engine can be operated as an air-motor driven by the previously stored pressurized air. The compressed air is stored in a pressure tank connected to one of the inlet ports. One of the engine inlet valves has been modified to work as a tank valve in order to control the pressurized air flow to and from the pressure tank. In order to switch between different modes of engine operation there is a need for a VVT system and the engine used in this study is equipped with pneumatic valve actuators that uses compressed air in order to drive the valves and the motion of the valves are controlled by a combination of electronics and hydraulics. This paper describes the introduction of new tank valve geometry to the system with the intent to increase the pneumatic hybrid regenerative efficiency. The new tank valve has a larger valve head diameter than the previously used setup described in order to decrease the pressure drop over the tank valve. In order to ensure tank valve operation during high in-cylinder pressures the valve is combined with an in-house developed pneumatic valve spring which makes the tank valve pressure compensated. A comparison between the old and the new tank valve geometry and their effect on the pneumatic hybrid efficiency has been done. Also, optimization of the valve timings for both CM (Compressor Mode) and AM (Air-motor Mode) has been done in order to achieve further improvements on regenerative efficiency.

A piezoelectric micro mass flow controller (MMFC) for liquid fuel injection into a mini-HCCI-motor for power generation is introduced. Piezoelectric actuation ensures negligible power consumption for fuel injection allowing self-sustaining operation. A pressurized fuel tank is connected to the MMFC which is designed like a normally-closed, on-/off-operating valve. Integrated piezoresistors are used for feedback control and an implemented pn-diode (sensitivity: -2.5 mV / K) enables on-chip temperature monitoring. Flow rates of up to 70 mul/s at 100 kPa fuel pressure have been demonstrated. The power consumption of the piezoelectric actuator during steady state operation is max. 20 muW at 120 V.

Urban traffic involves frequent acceleration and deceleration. During deceleration, the energy previously used to accelerate the vehicle is mainly wasted on heat generated by the friction brakes. If this energy that is wasted in traditional IC engines could be saved, the fuel economy would improve. One solution to this is a pneumatic hybrid using variable valve timing to compress air during deceleration and expand air during acceleration. The compressed air can also be utilized to supercharge the engine in order to get higher load in the first few cycles when accelerating. A Scania D12 single-cylinder diesel engine has been converted for pneumatic hybrid operation and tested in a laboratory setup. Pneumatic valve actuators have been used to make the pneumatic hybrid possible. The actuators have been mounted on top of the cylinder head of the engine. A pressure tank has been connected to one of the inlet ports and one of the inlet valves has been modified to work as a tank valve. The goal has been to test and evaluate 2 different modes – compression mode (CM) where air is stored in an air tank during deceleration and air-motor mode (AM) where the previously stored pressurized air is used for accelerating the vehicle. This paper also includes an optimization of the CM.

For developers of automotive control, prototyping and initial tests are a hassle. Commercial solutions are available but the price and especially the price/performance ratio opens the field for more cost effective solutions. Automotive rapid prototype systems seen so far are mainly processor based systems with standard interrupt driven measurement and actuation. Control systems based on high time resolution measurements of for example cylinder pressure are difficult to implement using these systems, neither is it possible to implement controller loops with an extremely high bandwidth in combination with expensive algorithms. Measurement and actuation within the same engine cycle, In Cycle Control (ICC) are not possible. The proposed system is based on a mixed system consisting of one standard x86 processor which is configured through Simulink and a reconfigurable application specific integrated circuit (an FPGA) configured either by relevant FPGA design tools or by Simulink. This layout of the rapid prototype system enables the designer to implement either ICC with very high bandwidth (only limited by the capacity of the injection system) or betweencycle control with medium bandwidth. The aim of this paper is to describe one possible configuration of such a system and to discuss the possible performance outcome of the final system.

HCCI combustion is well known and much results regarding its special properties have been published. Publications comparing the performance of different HCCI engines and comparing HCCI engines to conventional engines have indicated special features of HCCI engines regarding, among other things, emissions, efficiency and special feedback-control requirements. This paper attempts to contribute to the common knowledge of HCCI engines by describing an operational strategy suitable for a dual-fuel port-injected Heavy Duty HCCI engine equipped with a variable geometry turbo charger. Due to the special properties of HCCI combustion a specific operational strategy has to be adopted for the engine operation parameters (in this case combustion phasing and boost pressure). The low exhaust temperature of HCCI engines limits the benefits of turbo charging and causes pumping losses which means that “the more the merrier” principle does not apply to intake pressure for HCCI engines. It is desirable not to use more boost pressure than necessary to avoid excessively rapid combustion and/or emissions of NOx. It is also desirable to select a correct combustion phasing which, like the boost pressure, has a large influence on engine efficiency. The optimization problem that emerges between the need for boost pressure to avoid noise and emissions and, at the same time, avoiding an extensive decrease of efficiency because of pumping losses is the topic of this paper. The experiments were carried out on a 12 liter Heavy Duty Diesel engine converted to pure HCCI operation. Individually injected natural gas and n-Heptane with a nominal injection ratio of 85% natural gas and the rest n-Heptane (based on heating value) was used as fuel. The engine was under feedback combustion control during the experiments.

Engine tests have been performed on a 9.6 liter spark-ignited engine fueled by natural gas and a mixture of 25/75 hydrogen/natural gas by volume. The scope of the work was to test two strategies for low emissions of harmful gases; lean burn operation and stoichiometric operation with EGR and a three-way catalyst. Most gas engines today, used in city buses, utilize the lean burn approach to achieve low NOx formation and high thermal efficiency. However, the lean burn approach may not be sufficient for future emissions legislation. One way to improve the lean burn strategy is to add hydrogen to the fuel to increase the lean limit and thus reduce the NOx formation without increasing the emissions of HC. Even so, the best commercially available technology for low emissions of NOx, HC and CO today is stoichiometric operation with a three-way catalyst as used in passenger cars. The drawbacks of stoichiometric operation are low thermal efficiency because of the high pumping work, low possible compression ratio and large heat losses. The recirculation of exhaust gas is one way to reduce these drawbacks and achieve efficiencies that are not much lower than the lean burn technology. The experiments revealed that even with the 25 vol% hydrogen mixture, NOx levels are much higher for the lean burn approach than that of the EGR and catalyst approach for this engine. However, a penalty in brake thermal efficiency has to be accepted for the EGR approach as the thermodynamic conditions are less ideal.

Utilization of an ethanol driven, combustion-based power generator promises high-efficiency combustion in diesel-like engines and avoids problems connected to shrinking supplies of fossil fuels since fuels like ethanol or dimethyl ether can be produced from renewable resources. Fuel injection into such generator through a piezoelectric micro mass flow controller (MMFC) features low power consumption and enables self-sustaining operation: Only a negligible amount of generated power is re-used for injection and combustion control. A micro-machined MMFC with power consumption during steady state operation of 20 muW at 120 V is presented herein. The MMFC, which is designed like a normally-closed, on-/off-operating valve is connected to a pressurized fuel tank for testing and operation. Integrated piezoresistors are used for flow rate feedback control and an implemented pn-diode (sensitivity: -2.5 mV/K) enables on-chip temperature monitoring. Ethanol flow rates of up to 70 mul/s at 100 kPa fuel pressure have been demonstrated.

A control system for pneumatic variable valve actuation has been designed, implemented and tested in a single cylinder test engine with valve actuators provided by Cargine Engineering AB. The design goal for the valve control system was to achieve valve lifts between 2 and 12 mm over an engine speed interval of 300 to 2500 rpm. The control system was developed using LabView and implemented on the PCI 7831. The design goals were fulfilled with some limitations. Due to physical limitations in the actuators, stable operation with valve lifts below 2.6 mm were not possible. During the engine testing the valve lift was limited to 7 mm to guarantee piston clearance. Different valve strategies for residual gas HCCI combustion were generated on a singlecylinder test engine. (Less)

The Homogenous Charge Compression Ignition (HCCI) combustion engine has potential to replace the spark ignition and compression ignition engines of today. One of the main problems in making the engine commercially attractive is the lack of direct means of controlling the ignition phasing. In this paper, we investigate the potential of inlet air temperature as a means to ignition actuation. This article describes a method for system identification of the HCCI process, and development of an effective LQG regulator for the combustion process, Matlab and Simulink being used in computations and simulations.

An interest in measuring ion current in Homogeneous Charge Compression Ignition (HCCI) engines arises when one wants to use a cheaper probe for feedback of the combustion timing than expensive piezo electric pressure transducers. However the location of the ion current probe, in this case a spark plug, is of importance for both signal strength and the crank angle position where the signal is obtained. Different fuels will probably affect the ion current in both signal strength and timing and this is the main interest of this investigation. The measurements were performed on a Scania D12 engine in single cylinder operation and ion current was measured at 7 locations simultaneously. By arranging this setup there was a possibility to investigate if the ion current signals from the different spark plug locations would correlate with the fact that, for this particular engine, the combustion starts at the walls and propagates towards the center of the combustion chamber. The fuels investigated were isooctane, n-heptane, PRF80, gasoline, diesel, ethanol and methanol. A special interest was how the ion current timing was affected by low temperature reactions, which were present with the n-heptane and diesel fuels as well as mixtures of isooctane and n-heptane, i.e., PRF80. The most interesting results were that ion current is both affected by the ion current probe location in the combustion chamber and the fuel used. Fuels with higher octane numbers seem to provoke ion current more easily, thus with LTR fuels as n-heptane and diesel ion current was only achieved at richer mixtures. The cycle-to-cycle variations of ion current increased with leaner mixtures. Ion current was also affected by combustion phasing and engine speed. (Less)

In this paper the combustion chamber wall temperature was measured by the use of thermographic phosphor. The temperature was monitored over a large time window covering a load transient. Wall temperature measurement provide helpful information in all engines. This temperature is for example needed when calculating heat losses to the walls. Most important is however the effect of the wall temperature on combustion. The walls can not heat up instantaneously and the slowly increasing wall temperature following a load transient will affect the combustion events sucseeding the transient. The HCCI combustion process is, due to its dependence on chemical kinetics more sensitive to wall temperature than Otto or Diesel engines. In depth knowledge about transient wall temperature could increase the understanding of transient HCCI control. A ``black box'' state space model was derived which is useful when predicting transient wall temperature. To produce a model the engine is run with the load described by a Pseudo Random Binary Sequence (PRBS). Standard system identification methodology was then applied to acquire a state space model which calculate the combustion chamber wall temperature given IMEPn. Such a model is useful when controlling HCCI combustion and makes it possible to compensate the impact of wall temperature delay following a load transient.