Yudai Yamasaki

Diesel combustion model for on-board application

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.

Study on Model Based Combustion Control of Diesel Engine with Multi Fuel Injection

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 controllers performance was evaluated through simulation in which the combustion model was used as a plant model.

Combustion Characteristics of Small Size Gas Turbine Combustor Fueled by Biomass Gas Employing Flameless Combustion

One approach to achieving 99% combustion efficiency (C.E.) and 10 ppmV or lower NOx (at 15%O2 ) in a micro gas turbine (MGT) combustor fueled by biomass gas at a variety of operating conditions is with the use of flameless combustion (FLC). This paper compares experimentally obtained results and CHEMKIN analysis conducted for the developed combustor. As a result, increase the number of stage of FLC combustion enlarges the MGT operation range with low-NOx emissions and high-C.E. The composition of fuel has a small effect on the characteristics of ignition in FLC. In addition, NOx in the engine exhaust is reduced by higher levels of CO2 in the fuel.Copyright

Model-based control of diesel engines with multiple fuel injections:

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.

Operation of Micro Gas Turbine System Employing Two Stage Combustion of Biomass Gas

A two-axis, recuperated cycle micro-gas turbine (MGT) system for biomass gas is developed. The rated specifications of the MGT are as follows, pressure ratio of 2.7, turbine inlet temperature of 1120K, and output power of 5kW. The system consists of three components: the MGT power-generating system, control system and mock biomass gas supply system. The original two-stage combustor and H infinity system controller used in this system are discriminative. Since the gaseous fuel converted from biomass has a low heat quantity, the combustor is designed to achieve both high combustion efficiency and low NOx emission for lower calorific fuel. In the combustor, a stable tubular flame combustion of city gas in the first stage supplies burned gas, which has enthalpy and activated radicals, to the second stage and enables stable ignition and combustion of biomass gas and air premixture. In addition, because the gas composition of biomass gas is also affected by the sources, the gasification method, and the gasifying condition, the system controller is required to absorb fuel fluctuation while meeting the demanded output. Hence, the H infinity algorithm is employed as a system controller because of its robustness against disturbances from the unpredictable fuel component fluctuation. Using this MGT system, an operation test was carried out with mock biomass gases. The rotational speed of the power turbine could be kept almost constant with both mock fermentation gas and pyrolysis gas as the second-stage fuel, and NOx emission was 50ppm when load was increased to a rated power of 5kW. When the second-stage fuel composition changed from 100% methane to 50% methane and 50% CO2 at a certain speed, the power turbine speed could also be kept constant. The H infinity controller is compared with the 2-DOF PID controller for secondary fuel concerning the response to varying load. The former shows slightly better performance than the 2-DOF PID controller.Copyright

Simple combustion model for a diesel engine with multiple fuel injections

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.

Exhaust Gas Characteristic and Cost Evaluation of Gas Engines Compensating for Power Fluctuation of Renewable Energy

To utilize photovoltaic power generation (PV), the compensation for power fluctuation is necessary since the fluctuation has a bad influence on electric power system. Therefore, micro grid using several kinds of distributed generation is considered to be a good solution. For this reason, studies on batteries have been done in particular, due to the high output responsiveness. However, the power generation cost of batteries is higher than other distributed generation such as gas engines, which have not been studied enough from the viewpoint of distributed generation to compensate for renewable energy. In this paper, the feasibility of gas engines to compensate for the PV fluctuation is investigated from the point of view of exhaust gas NOx and power cost by simulation. As a result, the amount of NOx increases as the output of the gas engine fluctuates, but this increase on NOx hardly has a problem in micro grid. As for power cost, it can be decreased by combining battery and a few kinds of gas engines efficiently. In conclusion, it can be said that gas engines are able to play an important role in micro grid as distributed generation.