Go Tomatsu - The University of Tokyo, Department of Mechanical Engineering
東京大学大学院 工学系研究科・機械工学専攻・金子研究室 - 戸松 豪氏
Biomass gas is generated by fermentation or thermolysis of an organic substance in which combustible gases, such as methane (CH4), hydrogen (H2), and carbon monoxide (CO), as well as incombustible gases, such as carbon dioxide (CO2) and nitrogen (N2), are mixed together. The gas mixture ratio differs depending on the kind of biomass resources used as raw materials or the gasification method and changes from one moment to the next due to variations in the temperature in the gasifier. In addition, biomass gas contains much lower calorific gases (H2 and CO) and incombustible gases (CO2 and N2), and thus the calorific value is less than municipal gas, which may cause problems when running an engine.
To develop an engine that uses biomass gas fuel, we have to understand how the calorific value of fuel and differences in gas components affect the condition to run the engine. We conducted a combustion analysis for simulated biomass gas fuel in an engine running an experiment using simulated biomass gas fuel in which plural gas components are mixed together by an arbitrary ratio as the first step for developing the engine using biomass gas fuel.
In the engine-running experiment, the simulated biomass gas fuel generator supplies the simulated biomass gas fuel to the engine and data is acquired
In engine-running experiments using these apparatuses, synchronizing measurement signals, and improving efficiency in machinery operation during the experiment are two major problems.
To analyze and evaluate how differences in gas components in fuel affect the conditions necessary to run the engine, we measure various data such as the flow of fuel and air while the engine runs as well as the temperature and pressure at each spot in the engine. At this time, measurement synchronization with the movement of the engine crank is desirable for later analysis. The sampling rates need to be flexible because we sample pressure signals, which change quickly, every crank angle of one degree (9,000 Hz at the time of a rated engine speed of 1,500 rpm), and temperature, which changes relatively slowly, every revolution. Moreover, the range of output voltage differs depending on the sensor amplifier; therefore, we set the range at every channel to conduct more accurate measurements.
Engine Running Control
When the engine starts, we have to connect the clutch, rotate a self-starting motor, and disconnect the clutch when the fuel supply begins. Furthermore, while the engine is running, we have to adjust the flow of the air and fuel and the timing of ignition by operating actuators, such as the throttle, mass flow controller, and spark plugs to achieve experimental conditions that are set up in advance. Operating multiple pieces of equipment while the condition to run the engine is monitored during the experiment causes a large burden to the experimenter and requires efficiency improvements.
Generating Simulated Biomass Gas
Seven mass flow controllers independently monitor and control the flow of six kinds of gases (CH4, C2H4, H2, CO, CO2, and N2) and municipal gas 13A supplied from a cylinder. Therefore, we have to generate simulated biomass gas with an arbitrary mixture ratio and simultaneously operate seven controllers, which is a complicated process.
To simultaneously operate seven controllers, we use NI products to unify each input or output of the engine measurement apparatus and the simulated biomass gas fuel generator and construct systems for engine measurement control and simulated biomass gas fuel generation. We use LabVIEW to develop software for both systems.
For the engine measurement control system, we use an NI PXI-8176 controller, PXI-6071E analog input multifunction data acquisition (DAQ) module, a PXI-6733 high-speed analog output module, and PXI-6602 timing and digital I/O module. For conducting measurements, we use the PXI-6071E to sample outputs from the sensor at every crank angle on the basis of signals from a rotary encoder. For running control, we use the PXI-6733 modules to operate the actuators, such as the clutch, self-starting motor, throttle, and mass flow controller; and the PXI-6602 to generate ignition signals. The NI hardware unifies the I/O signals from each apparatus to be operated while running the engine. We constructed a system to run the engine and conduct measurements using a PC.
To develop the simulated biomass gas fuel generation system, we used a commercially available desktop PC and PXI chassis, a PXI-6031E analog input multifunction DAQ module, and a PXI-6733 module. Voltage inputs from the PXI-6733 control the flow of each gas component, and the PXI-6031E measures the actual flow. The PC simultaneously operates seven mass flow controllers, thus preparing the system to control the seven kinds of gas components of an arbitrary mixture ratio.
For the measurements, we successfully enabled synchronized sampling with the movement of the engine crank. Additionally, the software easily set the sampling rates per channel and the range of measurement. We conducted the test using only the PC, which simplified operation.
Moreover, we use LabVIEW to analyze the data. Everything from the experiment to analysis can be conducted using LabVIEW. Plural programming languages are not required, thereby reducing the corresponding time.
We used the data to analyze the performance of the engine, including outputs, thermal efficiency, the coefficient of change in outputs, and the characteristics of combustion, such as the timing when combustion starts and the duration of combustion, using an analysis program shown in Figure 2(b).
We successfully constructed a measurement control system for an engine using biomass gas fuel with LabVIEW. We constructed the system using software that provides flexible settings and can operate with a large number of I/O signals, which resulted in a reduction of burdens at the time of the experiment. In addition, everything from measurement to analysis could be conducted using LabVIEW, which enhanced our efficiency. Finally, when we manufacture a control system for the biomass gas fuel engine on an experimental basis, we can use the new system by changing only the software to further enhance development efficiency.
The University of Tokyo, Department of Mechanical Engineering