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One of the most difficult flow measurements for the automotive engineer is to measure the engine oil flow rate beneath operating conditions. With the engine mounted on a test bench and coupled to a dynamometer, the occupation is somewhat more comfortable due to the increased space availability, but none the less, careful selection and installation of the flow measurement scheme is required. Flow measurements required in the engine bay of a vehicle become further restricted due to instrument power requirement, installation space required and the harsh underneath bonnet conditions. What are the flowmeter options? Well, industry standards seem to subsist to a good deal of extent, but this does not mean they are correct. Let us look at a good deal of options. (1) The positive displacement meter, this could be in the form of a gear meter, piston meter or helical screw to name a few. These meters are in general on the higher cost side and may cause issues when installed due to their comparatively high pressure drop. Although rather good at operating throughout wide viscosities they do suffer from meter slippage at low viscosities. Meters vary in size, but may often times be installed without the need for any flow conditioning. Used by a great deal of engine test houses but not an idealisti solution. (2) Turbine flow meter, in general one of the most widely used flowmeters for engine oil flow measurement, principally due to it is low costs and little size. They may be purchased comparatively without apparent effort from a host of manufacturers and have a manageable pressure drop which is not too detrimental to oil scheme performance. They are sensible to oil and liquid flow profile effects, so it is exceedingly important to calibrate the flow meter all over the varying oil viscosity range and with it is installed upstream and downstream flow conditioning tubes. To ascertain exact results when in use, it is necessary to match the installed conditions as close as possible. Quite often specialist flow calibration laboratories will calibrate the flow meter on the same engine oil, at the same operating temperature and with the same inlet and outlet connections as per the installed engine. Sometimes this may be percentage of the engine assembly, such as an oil cooler or oil filter assembly, in general the easiest portion of the engine where the oil flow may be interrupted. Many flow meter makers only provide a calibration certificate on water, which may lead to exceedingly big errors if applied on engine oils. (3) Coriolis meters. Very good high accuracy meters, that would only be suitable to fixed installations. These meters stay highly highpriced and are huge in size, equated to the turbine and positive displacement meters. These meters have progressed well over the last 10 years, but may still be prone to poor installation, vibration and zero drift measurement errors. Ideal for test bench use where they are permanently installed, and with straight tube models now getting a norm, they offer low pressure drop and splendid viscosity rangeability. (4) Pressure Drop Characterization. An more and more mutual method for obtaining precise measurements without affecting the oil scheme performance due to insertion of flowmeters. Individual parts of the engine oil flow system are instrumented for pressure tapping emplacements and each engine percentage is flow characterized on a calibration bench for oil flow versus pressure drop at the required temperatures. Once each scheme has been characterized the engine is reassembled and tested, and the recorded pressure measurements are then applied to derive the flow rate. This method is in general applied on critical engine lubrication surveys, where the insertion of a flow meter would have a detrimental effect on the oil flow system. (5) Ultrasonic Clamp on meter. Although a non interfering device, due to it is straight pipe installation requirements, it does mean the scheme becomes interposing into the oil measurement system. Still highly pricey to purchase, and presently not sufficiently tested in these apps to become a suitable contender, altho progressing rapidly and without delay than most other techniques. Having decisive on your method of flow measurement, and undertook the required level of flow meter calibration throughout the range of operating temperatures, you are close to taking a rudimentary step forward in acquiring good flow measurement results. Engineers comparatively new to engine lubrication studies will have to seek counsel from the Flow Calibration Laboratory, who must be suitably experienced in this type of flow measurement application and be in a good position to find the best solution for your budget and flowmeter hardware inventory. Other Issues to bear in mind. The complex nature of engine oil flow measurement means it is very difficult to get exact oil flow readings from a running engine, but the informed engineer may make sound technology judgements on their measurement process. Keep in mind the influences of oil viscosity, oil temperature, meter installation effect on flowmeter and oil pump performance, oil aeration, relief valve effects and hysteresis, fuel dilution effects, engine oil levels, etc. The next series of discussions will delve deeper into the significances of these parameters in more detail. 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Flow Measurement Handbook: Industrial Designs, Operating Principles, Performance, and Applications