Development of Fuel Consumption Measurement Method for Fuel Cell Vehicle - Flow Method corresponding to Pressure Pulsation of Hydrogen flow - 2007-01-2008

Japan Automobile Research Institute (JARI) have developed the flow method as an easy way of measuring hydrogen consumption of fuel cell vehicles (FCVs) in real-time. A 2004 study on fuel consumption of five models of FCVs, measured by thermal flowmeters and based on gravimetric method, exhibited measurement errors within ±1% range for three models, but the errors were as large as -8% for two models that showed significant pulsation in hydrogen consumption flow. Assuming that the pulsation is the cause of errors in the flow method, we analyzed influences of pulsation in each flowmeter from two points (frequency and amplitude) and found that pulsation indeed caused flowmeter errors. Expansion chambers (Buffers) and throttle valves (regulators) were confirmed to have an effect in attenuating pulsation. Amplitude of pulsation shrunk to one tenths when such pulsation-reducing instruments were introduced between pulsating FCVs and flowmeters and were put to test. Fuel consumption was then measured using three types of flowmeters: thermal, sonic and differential-pressure. Results showed error reduction to about ±1% in fuel consumption test patterns in Japan and US, successfully improving the flow method. In our test, thermal flowmeters exhibited particularly high accuracy, with very little variation.