Experimental Setup

For the purpose of verifying air supply system controllability, an experiment on system components was conducted on the motor-driven blower + turbine compressor alternative, which alternative was chosen on account of its permitting various experimental conditions to be more easily set. A 2-stage rotary motor-driven blower was used, combined with a single-stage centrifugal automobile turbocharger driven by single-stage radial turbine. The system capacity was set at approximately 1/10 of'that for the envisaged actual ship. The experimental equipment is schematized in Fig. 1.

In the experiment, the following key items were examined, which are of interest in common with the turbine compressor + generator-motor alternative envisaged as ultimate choice.

- To verify the - operating stability of this system

- To determine the operating characteristics of the respective control systems, and to identify problems calling for solution

- To verify the controllability of the respective control systems under changes of load and of turbine inlet temperature

- To verify the starting characteristics and effect of startup load reduction provided by the compressor bypass line.

Air supply flow rate was' controlled by regulating the lst-stage blower, revolution.

Controllability of the air supply system was evaluated for the following alternative control methods:

(1) Without pressure control

Compressor delivery flow rate alone was controlled, and delivery pressure was left to follow its course. with no regulation intervening between turbine and compressor, all throttling loss is eliminated, to contribute toward raising the operating efficiency. The uncontrolled delivery pressure has proved to vary with such factors as the temperatures of environment and of turbine.

(2) Control of fuel cell outlet pressure

The control valve (V2 in Fig. 1) installed at fuel cell outlet was regulated to control the fuel cell outlet pressure. Closing this valve proved effectively to prevent dropping of fuel cell pressure upon such occurrences as abrupt lowering of turbine inlet pressure caused by turbine temperature decrease during operation under constant fuel cell load. It was further ascertained that the valve also provides a similar adjusting function upon lowering of turbine flow rate.

(3) Regulation of fuel cell bypass line flow rate

The rate of air supply to fuel cell from compressor delivery was adjusted by regulating the fuel cell bypass line control valve (V3 in Fig. 1). In practical application, this action is to be brought to play in partial load operation, when required to reduce the air supply to fuel cell to a level below minimum blower delivery rate.

Proper functioning of this action has been verified.

(4) Regulation of turbine bypass line flow rate

The turbine bypass line control valve (V4 in Fig. 1) serves to regulate the flow to turbine and lower the turbine inlet pressure. This action has proved to prevent abrupt rise of turbine inlet pressure upon such occurrences as turbine temperature rise during operation under constant fuel cell load. It has further been ascertained that the valve also provides a similar adjusting function against rise of turbine inlet pressure with increase of turbine flow rate.

An example of experimental results is shown in Fig. 2, representing a run on turbine compressor startup without use of the compressor bypass line. Further details are to be reported in poster session.

Table 1: Comparative evaluation of alternative air supply systems
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