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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.

Pilot injections are normally used for the reduction of diesel engine emissions and combustion noise. Nonetheless, with a penalty on the indicated thermal efficiency. The cost is reduced by the minimization of the pilot mass, which on its counterpart increases the risk of pilot misfire. Pilot misfire can have a higher penalty on the indicated efficiency if it is not compensated adequately. This paper investigates how in-cycle closed-loop combustion control techniques can reduce the effects of pilot misfire events. By closed-loop combustion control, pilot misfire can be detected and counteracted in-cycle. Two injection strategies are investigated. The first is the control of the main injection, the second includes an additional second pilot injection. Based on the in-cycle misfire diagnose, two architectures are investigated. The first uses a cycle-To-cycle controller to set the main injection under each scenario. The second is a fully in-cycle controller with feedback from predictive models. All the algorithms were tested experimentally in a Scania D13 engine. The results confirmed that in-cycle closed-loop combustion control can effectively reduce the effects of pilot misfire. An error of +1.5CAD on the main SOC and-0.5bar IMEP on the engine load was reduced to 0±0.6CAD and 0±0.4bar IMEP using the cycle-To-cycle architecture. The predictive in-cycle control can further reduce the error of the main SOC to 0±0.4CAD and 0±0.2bar IMEP for the engine load. These two approaches had one degree of freedom, and therefore only one of the combustion timing parameters (SOC or CA50) was regulated successfully. With the additional degree of freedom of the second pilot injection, the misfire effects were not only reduced, but also fully counteracted. The methods are limited by the time window where pilot misfire observability and controllability overlap. This is set by the injections' separations and the respective ignition delays. The second pilot injection can be further improved by the regulation of its injection timing and duration. The results can enhance the nominal set-up optimization by including the in-cycle controllability and regulation performance in the constraints. (Less)

Partially premixed combustion (PPC) is an advanced combustion concept and powertrain technology, which has a great potential to improve the fuel economy of vehicles. The process of PPC is driven by both chemical kinetics and mixing process, and is, therefore, sensitive to inlet conditions and injection process. This article presents a control-oriented combustion and air-path model of a PPC multicylinder engine, and also proposes a model predictive control framework for its transient control. The control system was validated in a transient scenario and its capability was demonstrated through a large range of load transient operation.

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.

Both numerical simulations and experiments were conducted in a heavy-duty DICI engine, with PRF81 as a gasoline surrogate, to investigate how the fuel stratification, auto-ignition and combustion are affected by the start of injection (SOI). The intake air temperature was adjusted to keep the combustion phasing constant when the SOI was swept from − 100 to − 20 oCA ATDC, covering different regimes of combustion, from HCCI to PPC. It is found that in the HCCI regime the combustion process is less sensitive to the variation of SOI since the fuel/air mixture is fairly homogeneous. The fuel/air mixture is under fuel-lean condition and the required intake temperature for a constant CA50 is the highest. In the PPC regime there is an optimal SOI window, within which the required intake temperature is the lowest to maintain a constant CA50 and the engine thermal efficiency is the highest. The optimal operation window starts at the SOI when all fuel is injected into the piston bowl and ends when the fuel injection is towards the bottom wall of the piston bowl, which results in a high heat transfer losses. The SOI window for optimal engine operation is expected to be fuel injector and piston bowl geometry dependent. During the transition regime, the fuel is injected towards the piston head in the squish region. The combustion process is highly sensitive to SOI due to the high sensitivity of fuel distribution in the cylinder to SOI. The engine thermal efficiency is the lowest due to the incomplete oxidation of fuel in the squish region.

For the reduction of emissions and combustion noise in an internal combustion diesel engine, multiple injections are normally used. A pilot injection reduces the ignition delay of the main injection and hence the combustion noise. However, normal variations of the operating conditions, component tolerances, and aging may result in the lack of combustion i.e. pilot misfire. The result is a lower indicated thermal efficiency, higher emissions, and louder combustion noise. Closed-loop combustion control techniques aim to monitor in real-time these variations and act accordingly to counteract their effect. To ensure the in-cycle controllability of the main injection, the misfire diagnosis must be performed before the start of the main injection. This paper focuses on the development and evaluation of in-cycle algorithms for the pilot misfire detection.Based on in-cylinder pressure measurements, different approaches to the design of the detectors are compared. For non-adaptive methods, a constant threshold, direct misfire probability, and posterior misfire probability detectors are investigated. For adaptive methods, an adaptive threshold update is suggested, an adaptation of the predictive stochastic models and a sensor fusion of them is proposed to increase the detection performance.A Scania D13 engine is used to perform the experiments under different operating conditions. The effectiveness of the algorithms is tested for different engine speeds, rail pressures, injection durations, starts of injection, EGR levels, and fuels. The results show that the observability of in-cycle pilot misfire depends on the operating conditions, and its detection can be performed successfully before the start of the main injection. With a maximum in-cycle pilot misfire observability of 98.5%, a maximum successful detection ratio of about 96% can be reached with the proposed in-cycle pilot misfire detectors. The algorithms are therefore suitable for in-cycle closed-loop combustion control feedback. By including cycle-to-cycle adaptation, the detection performance and robustness are improved significantly. The limitations are directly related to the signal-to-noise ratio of each operating condition. (Less)

Three injection strategies are compared in a light-duty (LD) diesel engine at a medium load point. One strategy, representative of a Euro 6 LD injection strategy, has a double-pilot/main/single-post sequence. There is a modest temporal spacing after the first pilot and second pilot. Additional strategies add a third pilot and greatly reduce the spacing after the pilots. These pilots are referred to as being “closely-coupled” to each other and the main injection. For the double-pilot strategy, there is significant undulation of the cylinder pressure around TDC. In contrast, the closely-coupled triple-pilot strategies show notably smaller undulations in their pressure traces. Despite increases in peak pressure rise rate, combustion noise is reduced in both triple-pilot strategies. An analysis of each strategy’s heat release rate (HRR) trace shows that the close spacing of the pilot injections drastically reduces the drop in HRR between each subsequent local peak in combustion from each injection. A new metric is developed in order to quantify these drops, called the Ratio of Reduced Heat Release (RRHR). It is found that in order to reduce combustion noise, the RRHR should be minimized. Further analysis into the combustion noise shows that the occurence frequency of the local HRR peaks matches strong frequencies responsible for combustion noise, and furthermore that the reduction in combustion noise is not due to the geometry of the combustion chamber. The modification of the HRR trace by implementing closely-coupled triple-pilot injection strategies allows combustion to be phased earlier, improving efficiency while also reducing combustion noise.

In order to significantly improve engine efficiency and reduce exhaust emissions at the same time, new radical combustion concepts have emerged. Gasoline partially premixed combustion (PPC) is one of them, with early results showing high gross indicated efficiency. To achieve that, PPC relies on high EGR (exhaust gas recirculation) use, with numbers that can reach up to 50%. Such a high amount of EGR poses a great demand on the gas exchange system, especially if it is not optimized for these requirements. A recent advancement that can provide high EGR rates especially under PPC conditions is the use of low pressure EGR, where gases are removed after the turbine and mixed with the intake air before the compressor. Experiments with the use of PPC and two different EGR routes were performed on a light duty Euro 6 2 L diesel engine. EGR sweeps between 100% use of long route to 100% short route under different conditions were performed. Gross indicated mean effective pressure (IMEPg) was kept around 10 bar, while four different speeds were used, 1200, 1800, 2400 RPM, as well as a reoccurring New European Driving Cycle (NEDC) speed-load point at 1500 RPM. To keep the fuel effects on combustion at a minimum, PRF 75 (Primary Reference Fuel) was used throughout the experiments. Results show that by combining EGR from both routes, generally, an optimum gas exchange efficiency can be found by splitting the EGR through both routes. This can be attributed to higher turbocharger efficiency due to better flow over the compressor regardless of engine load and speed. Emission wise, NOx emissions get an increase as EGR is moved from long route to short route, while soot emissions see an opposite trend for the same conditions. Based on these first results, a mixed EGR, or a long route system can be more beneficial for PPC type of engine applications.

[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.

Partially premixed combustion aims to reduce NOx and particulate matter emission without fuel consumption penalty. Low temperature heat release (LTHR) is an important process to be investigated. A novel motoring pressure prediction algorithm based on variable polytropic exponents was introduced and utilized to estimate average heat transfer coefficient as well as heat dissipation for real-time applications. A series of parameters, such as start of combustion (SOC) of LTHR, crank angle of 50% heat released (CA50) during LTHR, duration of LTHR and heat amount of LTHR, were further analyzed under different engine operation conditions. The results demonstrated that: (1) the absolute motoring pressure prediction error was below 0.5 bar with a relative error below 4%; (2) the average heat released during LTHR was about 40–65 J, and the mass burned was about 1–3% of the total mass burned; (3) CA50 of LTHR was more stable than SOC of LTHR, and was a better indicator for real-time combustion phase control; (4) similar combustion phase and heat amount of LTHR could be reached by adjusting the timing of the third injection regardless the difference in timing of the second injection; (5) the combustion phase and heat amount of LTHR could be controlled by the duration of the second injection.

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%.

This paper investigates how multiple in-cycle closed-loop combustion controllers can be integrated for a seamless operation under a wide-range of operating conditions. The stochastic cyclic variations of the combustion can be successfully compensated by the adjustment of the fuel injection pulses within the same cycle. The feedback information and controllability obtained relies on the different operating conditions, emissions regulations and fuels. Various in-cycle closed-loop combustion controllers are found in the literature to overcome the numerous challenges of the combustion control. In this paper, the modularization for the controller design and their integration is investigated, and how the transition between the available information, control actions and control strategy affects the final combustion behaviour. The approach consists in the design of a finite-state machine that supervises the transition between virtual sensors and measurements, regulators and the possibility of additional fuel injections. The proposed approach was tested in a Scania D13 engine for a wide-range of operating conditions. The results confirm the improved controllability and reduced steady-state RMSE of the controlled parameters, with a smoother transition between set-points, regardless of operating conditions and fuel.

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.

Adaptation of predictive combustion models for their use in in-cycle closed-loop combustion control of a multi-cylinder engine is studied in this article. Closed-loop combustion control can adjust the operation of the engine closer to the optimal point despite production tolerances, component variations, normal disturbances, ageing or fuel type. In the fastest loop, in-cycle closed-loop combustion control was proved to reduce normal variations around the operational point to increase the efficiency. However, these algorithms require highly accurate predictive models, whilst having low complexity for their implementation. Three models were used to exemplify the proposed adaptation methods: The pilot injection's ignition delay, the pilot burned mass, and the main injection's ignition delay. Different approaches for the adaptation of the models are studied to obtain the demanded accuracy under the implementation constraints. Non-linear adaptation techniques are necessary for the proposed models. This was compared to a linear formulation that reduced the complexity. A reduced multi-cylinder approach is presented as a method to reduce the total number of parameters while preserving the accuracy. A method to select the parameter for the reduction is also proposed. The sensitivity of the models and the robustness of the algorithms was studied. To reduce the complexity of the model implementation, the performance of Taylor's expansions was studied. The methods were tested from experimental data obtained from a Scania D13 six-cylinder heavy-duty engine run with conventional diesel, rape methyl-ester (RME), and hydrotreated vegetable oil (HVO). The adaptation of the models proved to significantly improve the prediction accuracy for each of the cylinders. The average bias error is eliminated whilst the total error dispersion was halved. The results validated the reduced multi-cylinder adaptation as a method to reduce the total number of parameters and have similar prediction accuracy. Furthermore, the multi-cylinder adaptation was the most robust against measurement errors. For the ignition delay models, the sensitivity to the nominal point of linearization was under the required prediction accuracy for the in-cycle closed-loop control algorithms i.e. under the detection accuracy of 0.2CAD. (Less)

A fuel mass estimation method for short pilot diesel injections is proposed and analyzed in this article. Previous studies showed that the pilot misfire ratio was more strongly correlated with the fuel mass than the on-time. This characteristic is exploited for the fuel mass estimation in a region where it is otherwise challenging to get good estimation accuracy due to the low signal-to-noise ratio, such as by rail pressure measurements or in-cylinder pressure for heat release estimation. The suggested method uses a Bayesian approach where the calibrated injectors, the pilot misfire ratio and the misfire detection are stochastically modelled. The effect of the different model parameters and dispersion on the estimator properties are analyzed. Experimental results in a Scania D13 Diesel engine confirm the improvement in the pilot mass estimation, for the regions within the transition from full misfire to full combustion. In this region, a 60% reduction in the estimation error was obtained, from 0.66mg to 0.27mg standard deviation.

Gas engines (fuelled with CNG, LNG or Biogas) for generation of power and heat are, to this date, taking up larger shares of the market with respect to diesel engines. In order to meet the limit imposed by the TA-Luft regulations on stationary engines, lean combustion represents a viable solution for achieving lower emissions as well as efficiency levels comparable with diesel engines. Leaner mixtures however affect the combustion stability as the flame propagation velocity and consequently heat release rate are slowed down. As a strategy to deliver higher ignition energy, an active pre-chamber may be used. This work focuses on assessing the performance of a pre-chamber combustion configuration in a stationary heavy-duty engine for power generation, operating at different loads, air-to-fuel ratios and spark timings. The engine was originally a 6-cylinder compression ignition engine which is here employed as a single cylinder engine and then suitably modified to host the pre-chamber (with its natural gas injection system and spark plug) with a new bowl piston to decrease compression ratio. A 0D model is built to make a thermodynamic analysis to characterize the local conditions in the pre-chamber before spark timing (temperature, pressure and composition), based on a compressible nozzle equation for the mass transfer between the chambers and a simplified Woschni model for the pre-chamber's heat transfer. A mathematical expression was found to describe the relationship between the local conditions and the early stage of the combustion. Experimental results showed the beneficial effect of spark delay and mixture leaning for the reduction of NOx emissions, while CO, unburned hydrocarbons and engine performance see improvement with lower air-to-fuel ratios and spark advance.

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).

Partially premixed combustion aims to reduce NOx and particulate matter emission without fuel consumption penalty. Low temperature reactions are important for the partially premixed combustion. In the current study, a self-adaptive strategy is introduced to predict the motoring pressure by means of an equivalent isentropic index. The start of the low temperature reactions is detected when the pressure difference between the measured pressure and the predicted pressure is higher than a threshold value. Experimental results show that the maximum variation between the measured and the predicted motoring pressure before the top dead center is less than 0.02 bar. It is also demonstrated that the presented detection method is able to detect the start of the low temperature reactions under different engine operating conditions with varying injection timing, injection duration, number of injections and exhaust gas recirculation rate.

In this paper, a virtual sensor for the estimation of the injected pilot mass in-cycle is proposed. The method provides an early estimation of the pilot mass before its combustion is finished. Furthermore, the virtual sensor can also estimate pilot masses when its combustion is incomplete. The pilot mass estimation is conducted by comparing the calculated heat release from in-cylinder pressure measurements to a model of the vaporization delay, ignition delay and the combustion dynamics. A new statistical approach is proposed for the detection of the start of vaporization and the start of combustion. The discrete estimations, obtained at the start of vaporization and the start of combustion, are optimally combined and integrated in a Kalman Filter that estimates the pilot mass during the vaporization and combustion. The virtual sensor was programmed in a Field Programmable Gate Array (FPGA), and its performance tested in a Scania D13 Diesel engine. The experimental results showed that the method can effectively improve the in-cycle pilot mass estimation. The accuracy, quantified by the average error between the actual injected mass and the estimated mass, was improved from an induced initial bias error of ±3 mg/st to a final error of ±0.1 mg/st, with a precision of ±0.45 mg/st. A level of precision of ±0.5 mg/st was already obtained at the peak of the pilot heat release. The suggested method is robust against changing operating conditions based on the calibration points. With the proposed parametrization, this is limited to regions where the parameter dependence is linear. The maximum calibration bias error for points out of the calibration range was within ±0.5 mg/st, with a precision of ±0.8 mg/st. In addition, the method was found to be robust against most input measurement errors and parameter bias. The major error sensitivity was detected for TDC offset. Different fuels than those used for calibration were found to result in an error proportional to the lower heating value error. The estimation framework can easily integrate more complex models to allow the estimation of greater pilot masses and multiple injections. The pilot mass estimation can be used to predict the pilot combustion and its effect on the main injection. This allows for better in-cycle controllability i.e. ability to adjust the main injection timing and duration, cycle-to-cycle control and adaptation of pilot and main injections. The closed-loop control of the combustion enables improved engine performance and efficiency, and reduced emissions variability. (Less)

An approach to reduce CO2 emissions while simultaneously keeping the soot emissions down from compression ignition (CI) engines is to blend in short chained oxygenates into the fuel. In this work, two oxygenated fuel blends consisting of diesel, gasoline and ethanol (EtOH) in the ratio of 68:17:15 and 58:14:30 have been utilized and studied in a single cylinder light duty (LD) CI engine in terms of efficiency and emissions. The reasons of utilizing gasoline in the fuel blend is due to the emulsifying properties it has while increasing the total octane rating of the fuel to be able to run the engine with a higher fraction of premixed flame. When performing the experiments, the control parameters were set as close as possible to the original equipment manufacturer (OEM) EU5 calibration of the multi-cylinder engine to study the possibility of using such blends in close to stock LD CI engines. With the oxygenates, in particular the fuel with the higher concentration of EtOH achieved an indicated net efficiency of ∼ 51% inf comparison to ∼ 47% for diesel at 8 bar BMEP. The NOX emissions increased slightly for the double injection strategy at 13 bar BMEP from ∼ 13.5 g/kW h to ∼ 14.5 g/kW h when going from diesel fuel to the higher ethanol blend. However utilizing single injection strategy at lower loads reduces the NOX. Highest soot mass measured for diesel was ∼ 0.46 g/kW h in contrast to ∼ 0.1 g/kW h for the oxygenates. Also, soot production when running the engine on the ethanol containing fuels was not significantly affected by EGR utilization as in the case of diesel. Considering particle size distribution, the particles are reduced both in terms of mean diameter and quantity. At 1500 rpm and 2 bar BMEP an increase of over ∼ 300% in THC and CO was measured, however, increasing the speed and load to above 2000 rpm and 8 bar BMEP respectively, made the difference negligible due to high in-cylinder temperatures contributing to better fuel oxidation. Despite having lower cetane numbers, higher combustion stability was observed for the oxygenates fuels.

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.

Methanol is an alternative fuel offering a lower well-to-wheel CO2 emission as well as a higher efficiency, given that the fuel is derived from biomass. In addition to reduced CO2, methanol does not emit soot particles when combusted which is a great advantage when attempting to reduce NOX levels due to the effectively non-existing NOX-soot trade-off. The engine setup used was a Scania D13 engine modified to run on one cylinder, utilizing a high compression piston with a rc of 27:1. This study analyzes the effects of four control parameters on gross indicated efficiency and the indicated specific emissions; CO, THC and NOX. The control parameters chosen in this work was common rail pressure (PRAIL), EGR, λ and CA50, running at 6 bar IMEPG and 1200 rpm. The effects of the control parameters on performance and emissions was analyzed using a surface response method of the Box-Behnken type. Predictive mathematical models were obtained from regression analysis performed on the responses from the experiments. The highest gross indicated efficiency achieved was ∼53%, when a high level of EGR was applied together with the combustion phasing set to its low level at CA50 = 6 CAD ATDC. The control parameters influencing the CO emissions are λ and the interaction between PRAIL and λ, while THC is only controlled by PRAIL and EGR. NOX emissions was, as expected, influenced mainly by EGR and λ, although PRAIL and CA50 also had minor effects. The effect of increased PRAIL, increased THC emissions which in its turn reduced the gross indicated efficiency. Throughout the experiment, THC concentration never decreased below ∼150 ppm due to utilization of high rc in combination with the volatility of methanol. It was also concluded that a rc = 27 is rather high if operation flexibility is required, especially at the higher load range.

Active pre-chamber configurations are considered a valuable solution for improving the operation of the internal combustion engine, in the view to overcome the many challenges it has been made to face. Combining this technology with the use of natural gas, a fuel that has increasing availability and interest in the market share, it is possible to burn ultra-lean mixtures (with air-to-fuel ratios, λ greater than 1.5) delivering reduced emissions and fuel consumption, without compromising efficiency and stability requirements. In this work three pre-chamber nozzles differing for the orifice diameter were tested in a stationary heavy-duty 6-cylinder engine (originally a compression ignition) converted to work with a single cylinder and spark ignition operated. An extensive test matrix was carried to perform spark timing, global lambda and load target sweeps in order to assess the behaviour of the three nozzles with respect to the changing operating conditions. Analysis of in-cylinder pressure traces and heat release rate have allowed to unveil the characteristics of the combustion phasing starting from the pre-chamber to the development in the main chamber, relating these to the performance of the engine in terms of emissions, efficiency and stability.

The engine concept partially premixed combustion (PPC) has proved higher gross indicated efficiency compared to conventional diesel combustion engines. The relatively simple implementation of the concept is an advantage, however, high gas exchange losses has made its use challenging in multi-cylinder heavy duty engines. With high rates of exhaust gas recirculation (EGR) to dilute the charge and hence limit the combustion rate, the resulting exhaust temperatures are low. The selected boost system must therefore be efficient which could lead to large, complex and costly solutions. In the presented work experiments and modelling were combined to evaluate different turbocharger configurations for the PPC concept. Experiments were performed on a multi-cylinder engine. The engine was modified to incorporate long route EGR and a single-stage turbocharger, however, with compressed air from the building being optionally supplied to the compressor. Experimental combustion heat release rates and boundary conditions were used to validate a simulation model. This model was then used to compare three different turbochargers: two single-stage turbochargers and one two-stage. The whole speed and load range was covered in the simulations to determine the engine performance. The influence of high EGR rates as well as the effect of charge air and EGR cooler gas outlet temperatures were also investigated. The simulation results showed that the two-stage turbocharger was able to give the highest load over the whole speed range with a brake mean effective pressure of 25.6 bar, whereas the two single-stage turbochargers reached 22.2 and 23.1 bar respectively. The average brake efficiency was 39.3, 39.7 and 40.2 %. It was found that decreasing the inlet temperature is critical for obtaining high loads and system efficiencies. Finally, it was shown that the optimal amount of EGR was dependent on the turbocharger efficiency and cooler temperatures.

Factors influencing pilot-injection combustion were investigated using heat release analysis in a heavy-duty diesel engine fuelled with standard diesel fuel. Combinations of pilot-injection parameters i.e. pilot start of injection, pilot mass, pilot-main injection separation, and rail pressure were studied for various operating conditions and combustion phases. An experiment was designed to investigate the factors influencing the combustion of the pilot. For improved injected fuel-mass accuracy, reference data for the injectors were measured in a spray rig prior to the engine experiments. Results show that cycle-to-cycle variations and cylinder-to-cylinder variations influence pilot autoignition and the amount of heat released. Rail pressure and injected pilot mass affect the obtained variance depending on the chamber conditions. The obtained combustion modes (premixed, diffusive) of pilot combustion were found to be a function of the injected mass and rail pressure. (Less)

A large number of measurement techniques have been developed or adapted from other fields to measure various parameters of engine particulates. With the strict limits given by regulations on pollutant emissions, many advanced combustion strategies have been developed towards cleaner combustion. Exhaust gas recirculation (EGR) is widely applied to suppress nitrogen oxide (NOx) and reduce soot emissions. On the other hand, gasoline starts to be utilized in compression ignition engines due to great potential in soot reduction and high engine efficiency. New engine trends raise the need for good sensitivity and suitable accuracy of the PM measurement techniques to detect particulates with smaller size and low particulate mass emissions. In this work, we present a comparison between different measurement techniques for particulate matter (PM) emissions in a compression ignition engine running on gasoline fuel. A wide-range of EGR was used with lambda varied from 3 down to 1. The compared equipment includes AVL smoke meter, AVL Micro Soot Sensor, Pegasor and Cambustion Differential Mobility Spectrometer (DMS). The goal of this paper is to compare the recorded values and show the sensitivity of the instruments to soot properties altering, in both lean and stoichiometric combustion situations. (Less)

Advanced combustion such as the partially premixed combustion (PPC) is characterized by high energy efficiency. However, they are sensitive to the inlet condition and injection of a combustion engine. Therefore, it is essential to use combustion feedback. The accuracy of the feedback variables, derived from the cylinder pressure signal, is crucial for effective combustion feedback control. This paper proposes a nonlinear least-squares regression method to estimate the pressure offsets and variable polytropic exponent in heat release calculation automatically. The combustion feedback variables derived from the auto-tuned heat-release rate were applied to a heavy-duty compression ignition (CI) engine burning with gasoline fuel. [DOI: 10.1115/1.4042877] (Less)

The double compression-expansion engine concepts (DCEE) are split-cycle concepts where the compression, combustion, expansion and gas exchange strokes occur in two or more different cylinders. Previous simulation studies reveal there is a potential to improve brake efficiency with these engine concepts due to improved thermodynamic and mechanical efficiencies. As a continuation of this project this paper studies an alternative layout of the DCEE-concept. The concept studied in this paper has three different cylinders, a compression, a combustion and an expansion cylinder. Overall system indicated and brake efficiency estimations were based on both engine experiments and simulations. The engine experiments were carried out at 10 different operating points and 5 fuelling rates (between 98.2 and 310.4 mg/cycle injection mass) at an engine speed of 1200 rpm. The inlet manifold pressure was varied between 3 and 5 bar. Due to concerns with structural stability the peak cylinder pressure during the engine experiments was limited to 210 bar. Exhaust backpressure was limited to 8 bar due to thermal stress on the exhaust valves. The engine experiments reveal that a gross indicated efficiency (GIE) of 47 % is achieved at most of the operating points. There were cases where GIE was below 45 % due to high heat loss and degraded combustion efficiency.The data obtained from the engine experiments were then used as input into the full DCEE-engine simulations. System brake efficiency was determined by estimating friction loss in the simulations. These simulations and friction estimations suggests a system brake efficiency of 41.8 % at the lowest fuelling rate (98.2 mg/cycle) is achieved. Increasing engine load improves efficiency due to lower relative intercooling loss and improved mechanical efficiency. A peak system brake efficiency of 52.8 % is achieved at a very high injection mass (275.6 mg/cycle) and 5 bar Pinlet setting. A further increase in injection mass to 310.4 mg/cycle results in a high increase in heat loss which causes system brake efficiency to decrease to 49.9 %. (Less)

The double compression expansion engine (DCEE) is a promising concept for high engine efficiency while fulfilling the most stringent European and US emission legislation. The complete thermodynamic cycle of the engine is split among several cylinders. Combustion of fuel occurs in the combustion cylinder and in the expansion cylinder the exhaust gases are over expanded to obtain high efficiency. A high-pressure tank is installed between these two cylinders for after-treatment purposes. One proposal is to utilize thermal reduction of nitrogen oxides (NOx) in the high-pressure tank as exhaust temperatures can be sufficiently high (above 700 °C) for the selective non-catalytic reduction (SNCR) reactions to occur. The exhaust gas residence time at these elevated exhaust temperatures is also long enough for the chemical reactions, as the volume of the high-pressure tank is substantially larger than the volume of the combustion cylinders. In this paper a single-cylinder D13 engine was run together with a 30 l high-pressure tank, with and without a diesel oxidation catalyst (DOC). AUS 32 and an ammonia-water solution (AAS 25) are injected before the high-pressure tank at different exhaust temperatures to study the thermal reduction of NOx produced from the combustion and the impact of the DOC. Additionally, the normalized stoichiometric ratio (NSR) was swept to evaluate the maximum NOx reduction potential of SNCR. Experimental results showed that very high NOx conversion efficiencies could be achieved for both AUS 32 and AAS 25. NOx conversion efficiencies of 80 % were obtained for NSR = 3. At stoichiometric NOx reductant dosing (NSR = 1), 40 % of nitrogen oxides could be reduced thermally. Presence of a DOC would decrease the efficiency of the thermal reduction as it oxidizes ammonia. At exhaust gas temperatures below 400°C, platinum in the DOC reduced NOx with a maximum conversion efficiency of 31 % at 350°C. (Less)

The combustion processes of three injection strategies in a light-duty (LD) diesel engine at a medium load point are captured with a high speed video camera. A double-pilot/main/single-post injection strategy representative of a LD Euro 6 calibration is considered as the reference. There is a modest temporal spacing (dwell) after the first pilot (P1) and second pilot (P2). A second strategy, "A," adds a third pilot (P3). The dwell after both P2 and P3 are several times shorter than in the reference strategy. A third strategy, "B," further reduces all dwells. Each injection has its own associated local peak in the heat release rate (HRR) following some ignition delay. Between these peaks lie local minima, or dips. In all three cases, the fuel from P1 combusts as a propagating premixed flame. For all strategies, the ignition of P2 primarily occurs at its interface with the existing combustion regions. Extinguishing of the prevailing combustion by the fuel jets of later injections is noted in all strategies. This phenomenon is confirmed by comparing the timing of each fuel injection with the dips in the HRR and spatial luminescence over time. These dips after each injection are larger than would be expected by the cooling effect of the injected fuel alone. Furthermore, not all dips in the HRR are the result of this extinguishing, and it would not have been possible to determine if the dips are due to this extinguishing or a simple exhaustion of available fuel without this optical investigation. Even if the precise hydraulic injection timing can be known, knowledge of the spatial relationship of the injected fuel and prevailing combustion is necessary. (Less)

NOx pollution from diesel engines has been stated as causing over 10 000 pre-mature deaths annually and predictions are showing that this level will increase [1]. In order to decrease this growing global problem, exhaust after-treatment systems for diesel engines have to be improved, this is especially so for vehicles carrying freight as their use of diesel engines is expected to carry on into the future [2]. The most common way to reduce diesel engine NOx out emissions is to use SCR. SCR operates by injecting aqueous Urea solution, 32.5% by volume (AUS-32), that evaporates prior the catalytic surface of the SCR-catalyst. Due to a catalytic reaction within the catalyst, NOx is converted nominally into Nitrogen and Water. Currently, the evaporative process is enhanced by aggressive mixer plates and long flow paths. The mixer plates create extra exhaust back pressure and cool the exhaust gases, which decreases engine and catalyst efficiency, resulting in overall poor NOx conversion (

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.

The focus has recently been directed towards the engine out soot from Diesel engines. Running an engine in PPC (Partially Premixed Combustion) mode has a proven tendency of reducing these emissions significantly. In addition to combustion strategy, several studies have suggested that using alcohol fuels aid in reducing soot emissions to ultra-low levels. This study analyzes and compares the characteristics of PM emissions from naphtha gasoline PPC, ethanol PPC, methanol PPC and methanol diffusion combustion in terms of soot mass concentration, number concentration and particle size distribution in a single cylinder Scania D13 engine, while varying the intake O2. Intake temperature and injection pressure sweeps were also conducted. The fuels emitting the highest mass concentration of particles (Micro Soot Sensor) were gasoline and methanol followed by ethanol. The two alcohols tested emitted nucleation mode particles only, whereas gasoline emitted accumulation mode particles as well. Regarding soot mass concentration measurements; methanol never exceeded 1.6 mg/m3 while when operating on gasoline this value never descended below 1.6 mg/m3. From this result it can be concluded that the main contributor to PM mass emissions is mainly increasing CMD (Count Mean Diameter) in the accumulation mode size range, but can in diffusion combustion also be caused by a high amount of nucleation mode particles. A probable cause of higher particle number emissions, when running the engine on methanol compared to ethanol, is the corrosiveness of the fuel itself. Except for the ultra-low PM mass emitted from alcohol combustion, it is also possible to alter the EGR concentration with a higher level of freedom without having to consider the NOX - soot tradeoff.

Model-based analysis of in-cylinder pressure sensor signals has been a key component for internal combustion engine research, diagnostics and controller development during the past decades. This analysis is often based on simple thermodynamic models of the in-cylinder processes. In order for the analysis to give accurate results, the models need to be sufficiently calibrated. This paper investigates the use of the extended Kalman filter and the particle filter for the purpose of online estimation of top-dead-center offset, a convective heat-transfer coefficient and cylinder-wall temperature in a Gatowski heat-release model. Simulation results show that the filters are consistent in estimating the true parameters, that the assumed model uncertainty and heat-release noise density works as filter tuning parameters. The filters were found to be sensitive to errors on pressure-sensor offset and the cylinder compression ratio. The filters were also evaluated against experimental data and the result showed converge times of 200 engine cycles with acceptable steady-state variance for both filters. (Less)

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)

Partially Premixed Combustion (PPC) has been proved a high efficiency combustion concept, along with ultra-low soot and NOx emissions. However, the nature of high pressure rise rate prevents PPC from operating range extension and further practical use. This paper aims to optimize mixture preparation to achieve the benefits of PPC with the constraints of engine states through injection strategy during transient operation. A control-oriented model (COM) is developed based on double-Wiebe function to predict combustion process, where a new linear algorithm is proposed to identify the model parameters. The root mean square error (RMSE) of the predicted cylinder pressure is less than 2.58 bar and peak error is less than 5% against experimental measurements of steady states. A constrained model predictive controller (MPC) is designed and implemented in a PPC engine. Simulation and experiment results show that the proposed controller manipulates injection events to optimize premixing period and fuel distribution towards more benefits of PPC concept. In the testing scenario, soot, NOx and pressure rise rate are regulated within 0.15 mg/m3, 400 ppm and 8 bar/deg, respectively. Consequently, cumulative soot and NOx emissions are reduced by 43.2% and 6.8% in the whole transient cycle.