In our project we are using CNG, Hydrogen as fuel for IC engine. We need to measure the flow rate of the above. We want to do it without flow-meter/rotometer. Please, suggest methods which will be low cost.
3 options are available:
1- use a coriolis mass flow meter (accurate but very expensive)
2- use a ultrasonic flow meter (should be Ex) (fair price)
3- use a thermal mass flow meter (should be Ex) (fair price)
Ultrasonic flow measurement works very well for measuring gaseous flows. If you are also measuring intake airflow (LFE, hot-wire or ultrasonic) and exhaust lambda (zirconia UEGO sensor), then you may not need to measure fuel flow since it can be very precisely calculated based on intake air mass flow and exhaust lambda using an oxygen balance equation. I have found the oxygen balance method of calculating fuel mass flow can often provide a higher degree of precision under transient operating conditions than direct fuel flow measurement.
Dear Joseph can you please provide the reference for the method which you found.
I am not aware of a good citation for this. There are a series of chemical mass balance equations published within the EPA exhaust emissions measurement procedures which, if you solve for measured A/F from exhaust O2 measurement (oxygen-balance instead of carbon-balance), will result in the simple calculation that I provide below (see 40 CFR §1065.655 available at www.ecfr.gov for chemical mass balance examples). Unfortunately, §1065.655 does not provide a specific oxygen balance example but the concept is pretty simple.
Laboratory UEGO sensors and their associated signal conditioning hardware typically provide linearized analogue output channels for exhaust lambda (measured A/F ratio normalized by stoichiometric A/F ratio) and exhaust oxygen concentration (or "deficit" in the case of reducing conditions). When calibrated vs. known standards and when the fuel properties (e.g., stoichiometric A/F) are known, they can provide precise, accurate and very fast A/F measurement - fast enough to resolve per-firing-cycle fuel control in an engine. At a particular operating condition, if you measure A/F via zirconia-UEGO and simultaneously measure intake air flow, then exhaust flow can be calculated by simply:
(air-mass-flow) / (A/F ratio)=(fuel mass flow)
UEGO measurements are fairly commonplace within engine-dynamometer test cells and are routinely used during vehicle and engine development. Such measurements are also critical when developing engine emissions control systems. The instrumentation can be fairly low-cost, particularly considering the critical information that it provides during engine experiments. The sensors are massed produced automotive sensors used in low-emission vehicle applications and there are "DIY" kits commercially available to provide control and signal conditioning for UEGO sensors.
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