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The purpose of this study is to develop a model for the gas exchange process in a rebreathing homogeneous charge compression ignition (HCCI) engine. HCCI engines are attracting significant attention due to their low emissions and high efficiency. To design the control system of an HCCI engine, it is necessary to develop a control-oriented engine model. The developed model lowers its computational load by combining two types of models. The model consists of a discrete model for the exhaust process (the first half of the gas exchange process) and a continuous model with a variable calculation step size for the rebreathing process (the latter half of the gas exchange process). Also, the constructed model maintained its prediction accuracy, as the pressure pulsation in the exhaust port was modeled, and an unsteady flow equation was used. It was confirmed that the model developed for the gas exchange process calculated in about half time of one cycle and reproduced the results of 1D engine simulation software with a maximum error of about 10% in the in-cylinder pressure, temperature, and trapped mass.

Model-based control systems are drawing attention in relation to implementing advanced combustion technologies with high thermal efficiency and low emissions, such as homogeneous charge compression ignition and premixed charge compression ignition combustion, having low robustness. A model-based control system for engine combustion derives control inputs based on reference values and operating conditions in each cycle. Thus, it can replace the conventional control map, which necessitates a significant number of experiments. However, model-based control for combustion requires reference values, such as heat-release-rate peak timing and value, which represent the combustion state. In addition, because model-based control systems derive control inputs cycle by cycle, the combustion reference for the transient condition is critical for maximizing the benefit of such systems. Therefore, this study describes a design method of the combustion reference values for transient operation. The combustion method targeted in this study is a premixed compression ignition combustion that exhibits two-stage heat releases and can reduce combustion noise. Particularly, a method using predicted future operating conditions considering the driving characteristics is proposed. Designed combustion reference values with the proposed method were evaluated with engine control experiments in a certain part of worldwide harmonized light vehicles test cycle. Results indicate that the rate of achieving the desired two-stage heat releases combustion improved from 57% to 81% and combustion noise reduced. Thus, designing the combustion reference values for transient operation by considering future operating conditions is effective to ensure advanced combustion. In addition, such a method can consider the driving characteristics.

The dual-fuel engine (DFE) has been focused on in order to improve its efficient use of natural gas. It has been reported that in DFE the combustion efficiency of the natural gas decreases at a low load. In an attempt to tackle this problem, it has been reported that a multi-stage diesel injection can improve the combustion efficiency of natural gas at a low load. The aim of this research is, therefore, to explain the mechanism for improving combustion efficiency with a multi-stage diesel injection and to develop a control model that predicts engines' combustion efficiency by multi-stage injection. Additionally, a controller was developed using the control model to improve the combustion efficiency by changing the diesel injection conditions. Experimental results show that the controller improves combustion efficiency. Furthermore, taking in to account the heat ratio of natural gas to diesel fuel in addition to combustion efficiency, it has been shown that it is possible to design a controller to leverage the advantage of DFE, which reduces the quantity of fossil fuels.

In this study, a multiple-input multiple-output feedforward controller for use with multiple-point fuel injection systems is applied to a diesel engine using an original control-oriented model. The target-tracking performance of this multiple-input multiple-output feedforward controller was then tested in terms of how well the controller adjusts the fuel delivery ratios to the pilot injection, pre-injection, main fuel injection, and the main fuel injection timing, and controls the in-cylinder peak pressure and its timing. Control experiments are conducted at different engine outputs and speeds while changing the targets of the in-cylinder peak pressure and its timing. The controller is able to track the varying targets within an acceptable error included in the original model. The calculation time, which is almost double that of a single-input single-output controller, is sufficiently fast to derive the applicable inputs.

This paper deals with a combustion control system design problem for diesel engines. The consider combustion in this paper is a premixed diesel combustion which produce a dual peak heat release rate. This combustion has high thermal efficiency and low NOx and PM emissions. However, in order to implement this combustion, it is required to design a robust combustion control system because this combustion is low robust with respect to changes of the engine state. Therefore, in this paper, we design an adaptive output feedback control system by considering the in-cylinder heat release rate as the output to be controlled. The effectiveness of the proposed method is confirmed through numerical simulations and experiments on a practical diesel engine.

We developed a feed-forward controller for a conventional diesel combustion engine with triple fuel injection and experimentally evaluated its performance. A combustion model that discretizes an engine cycle into a number of representative points to achieve a light calculation load is embedded into the controller; this model predicts the in-cylinder gas-pressure-peak timing with information about the operating condition obtained from the engine control unit. The controller calculates the optimal main-fuel-injection timing to control the in-cylinder gas-pressure peak using the prediction result as a controller with a single input and output. The controller’s performance was evaluated by experiments using a four-cylinder diesel engine under changing the target value of the in-cylinder gas-pressure-peak timing during a target-following test and the performance was also evaluated under changing the exhaust gas recirculation ratio at the constant target value of the in-cylinder gas-pressure-peak timing for the disturbance-response test. It was found that the controller could calculate the optimal main-injection timing over a cycle and maintain the targeted in-cylinder gas-pressure-peak timing even when the target value or exhaust gas recirculation changed. The combustion model was also shown to be fast enough at predicting diesel combustion for onboard control.

Engine systems must continuously increase their thermal efficiencies and lower their emissions in real operation. To meet these demands, engine systems are increasingly improving their transient performance through control technology. Conventional engine control systems depend on control maps obtained from huge numbers of experiments, which is necessarily limited by the available number of man-hours. These time-consuming control maps are now being replaced by control inputs derived from on-board models. By calculating optimized control inputs in real time using various information, model-based control increases the robustness of advanced combustion technologies such as premixed charge compression ignition and homogeneous charge compression ignition, which use auto-ignition and combustion of air–fuel mixtures. Models also incur relatively low computational loads because the specifications of the engine control unit are lower than those of current smartphones. This article develops a simple diesel combustion model with model-based control of the multiple fuel injections. The model employs the discretized cycle concept based on fundamental thermodynamic equations and comprises simple fuel injection and chemical reaction models. Our control concept aims mainly to decrease the fuel consumption by increasing the thermal efficiency and reduce the combustion noise in real-world operation. The model predicts the peak in-cylinder gas pressure and its timing that minimize the combustion noise and maximize the thermal efficiency, respectively. In an experimental validation of the model, the computed and measured in-cylinder pressures were well matched at each phase under various parameter settings. In addition, the calculation time of the model is sufficiently short for on-board applications. In future, the proposed model will be extended to the design and installation of controllers for engine systems. The control concept and associated problems of this task are also described in this article.

Diesel engines exhibit highly efficient, environmentally sound performance under good operational control; however, because of the demand of controlling multiple actuators under various environmental conditions, the conventional experimental method for controlling diesel engines has become increasingly difficult. Therefore, diesel combustion models with less calculation loads were ultimately developed with the aim of implementing such model-based controllers for engine control unit in the future. To achieve the on-board application of the diesel combustion model, the in-cylinder state of a single cycle was discretized into several representative phases such as a valve-opening and valve-closing phase, ignition phase, and maximum pressure phase. Temperature and oxygen quantities in residual gas were considered as the state variables of the system because they have a critical effect on combustion and induce cyclic coupling. The model could take account of the effect of actuators in diesel engines, and the states in each phase were calculated by fundamental thermodynamic equations and some empirical equations. The model was validated against experimental results and had a good agreement with in-cylinder pressures and temperatures at each phase. In addition, the calculation times of the model were confirmed to be capable of on-board application. Furthermore, as a demonstrative example and to show the added value of the model, it was used to synthesize controllers to enable multi-input/multi-output control of a diesel engine in simulation.

The need for reductions of nitrogen oxides (NOx), sulfur oxides (SOx), and carbon dioxide (CO2) emissions has been acknowledged on the global level. However, it is difficult to meet the strengthened emissions regulations by using the conventional marine diesel engines. Therefore, lean burn gas engines have been recently attracting attention in the maritime industry. Because they use natural gas as fuel and can simultaneously reduce both NOx and CO2 emissions. On the other hand, since methane is the main component of natural gas, the slipped methane, which is the unburned methane emitted from the lean burn gas engines, might have a potential impact on global warming. The authors have proposed a combined exhaust gas recirculation (C-EGR) system to reduce the slipped methane from the gas engines and NOx from marine diesel engines by providing the exhaust gas from lean burn gas engine to the intake manifold of the marine diesel engine using a blower. Since the exhaust gas from the gas engine includes slipped methane, this system could reduce both the NOx from the marine diesel engine and the slipped methane from the lean burn gas engine simultaneously. This paper introduces the details of the proposed C-EGR system and presents the experimental results of emissions characteristics on the C-EGR system. As a result, it was confirmed that the C-EGR system attained more than 75% reduction of the slipped methane in the intake gas. Additionally, the NOx emission from the diesel engine decreased with the effect of the exhaust gas recirculation (EGR) system.

In this paper, a gas engine system capable of stable operation at any mix ratio of city gas 13A and biogas was developed. The gas engine system consists of a spark-ignition gas engine, an additional electric throttle valve for fuel and our own control algorithm. The engine is a 3-cylinder 1.6-l engine that was originally used for co-generation, and the fuel throttle valve was added to respond to different fuel compositions. The control algorithm was also designed to adjust the fuel and air ratio to attain a higher generation efficiency and lower NOx emission with different mix ratios of city gas 13A, biogas and load. Before developing the controller, the effect of the mix ratio on generation efficiency and NOx emission was investigated under various load conditions. The following summarizes the experimental results: a control algorithm using the Wobbe index for mixed fuels was formulated; this index determines the target fuel-to-air ratio. Next, operation tests were performed under varying fuel mix ratios and loads by applying the control algorithm to the gas engine. The target engine rotational speed and exhaust O 2 concentration was realized in 5 s when the biogas fraction varied from 20% to 40% and from 70% to 40%. When the load was also varied from 9.4 kW to 0.5 kW and from 0.5 kW to 9.4 kW at a constant rate, the rotational speed and exhaust O 2 concentration achieved the target values in 20 s. Under both transient operation conditions, the engine system met the NOx emission requirement, and the results indicate that the simple hardware modification to a conventional gas engine and our original control algorithm are capable of achieving stable engine operation at any mix ratio of city gas 13A and biogas.

In this study, the authors aim to develop a small gas engine system for biomass gas by modifying the control system of a conventional spark ignition engine. Before developing a control algorithm, combustion experiments with various component fuels assumed to have the components of real biomass gases, such as fermentation and pyrolysis gases, were carried out. It was clarified that the relationship between dimensionless combustion duration and equivalence ratio can be expressed by a first-order linear function regardless of fuel composition. Indicated thermal efficiency can also be expressed by combustion duration and volumetric efficiency when the coefficient of variation of indicated mean effective pressure is lower than 5% and pumping loss decreases against volumetric efficiency linearly, and the relationship between combustion duration and MBT can also be expressed by a first-order function. By using these relationships, a gas engine control algorithm, which can define the target values of the equivalence ratio of a premixture and ignition timing that realize a high thermal efficiency for fuel compositions automatically by analyzing in-cylinder gas pressure data in real time, is developed in order to use gaseous fuels produced from biomass resources effectively. Thus, a biomass gas fuel engine system is developed by applying the algorithm to an automobile gasoline engine, hardware modifications of which are only the fuel supply system and flywheel. The engine system is connected to a gasification plant using wood chips and an operation test is carried out. As a result, the engine system can set an optimum premixture condition and an ignition timing, which realizes a stable and high-thermal-efficiency operation automatically.

A controller for model-based control of diesel engine with triple injection were developed with a combustion model. In the combustion model, an engine cycle is discretized into several representative points in order to improve calculation speed, while physical equations are employed to expand the versatility. The combustion model can predict in-cylinder pressure and temperature in these discrete points. Prediction accuracy of the combustion model was evaluated by comparison with experimental result. A controller was designed with the combustion model in order to calculate optimal fuel injection pattern for controlling in-cylinder pressure peak timing. The controller's performance was evaluated through simulation in which the combustion model was used as a plant model.

In the HCCI (Homogeneous Charge Compression Ignition) engine, a mixture of fuel and air is supplied to the cylinder and auto-ignition occurs resulting from compression. This method can expand the lean flammability limit, realizing smokeless combustion and also having the potential for realizing low NOx and high efficiency. The optimal ignition timing is necessary in order to keep high thermal efficiency. The Ignition in the HCCI engine largely depends on the chemical reaction between the fuel and the oxidizer. Physical methods in conventional engines cannot control it, so a chemical method is demanded. Combustion duration is maintained properly to avoid knocking. In addition, the amount of HC and CO emissions must be reduced. The objective of this study is to clarify the following through calculations with detailed chemical reactions and through experiment with the 2-stroke HCCI engine: the chemical reaction mechanism, and HC and CO emission mechanisms. Ignition and combustion mechanisms and the effect of pre-mixture heterogeneity on ignition and combustion are also clarified. This is done by using an optically accessible engine and measuring the luminescence at auto-ignition and during the combustion process.