One of the most difficult flow measurements for the automotive engineer is to measure the motor oil flow rate under operating conditions. With the motor mounted on a test bench and coupled to a dynamometer, the job is slightly easier due to the increased space availability, but none the less, meticulous option and premise of the flow determination system is required. Flow measurements required in the motor bay of a vehicle come to be additional restricted due to instrument power requirement, premise space required and the harsh under bonnet conditions.
What are the flowmeter options? Well, business standards seem to exist to some extent, but this does not mean they are correct. Let us look at some options.
Clamp Meter
(1) The obvious displacement meter, this could be in the form of a gear meter, piston meter or helical screw to name a few. These meters are generally on the higher cost side and can cause issues when installed due to their relatively high pressure drop. Although quite good at operating across wide viscosities they do suffer from meter slippage at low viscosities. Meters vary in size, but can often be installed without the need for any flow conditioning. Used by some motor test houses but not an ideal solution.
(2) Turbine flow meter, generally one of the most widely used flowmeters for motor oil flow measurement, mainly due to its low costs and small size. They can be purchased relatively undoubtedly from a host of manufacturers and have a manageable pressure drop which is not too detrimental to oil system performance. They are sensitive to oil and fluid flow profile effects, so it is very prominent to calibrate the flow meter across the varying oil viscosity range and with its installed upstream and downstream flow conditioning tubes. To ensure precise results when in use, it is requisite to match the installed conditions as close as possible. Quite often master flow calibration laboratories will calibrate the flow meter on the same motor oil, at the same operating climatic characteristic and with the same inlet and outlet connections as per the installed engine. Sometimes this may be part of the motor assembly, such as an oil cooler or oil filter assembly, generally the easiest part of the motor where the oil flow can be interrupted. Many flow meter manufacturers only supply a calibration certificate on water, which can lead to very large errors if used on motor oils.
(3) Coriolis meters. Very good high accuracy meters, that would only be superior to fixed installations. These meters remain very high-priced and are large in size, compared to the turbine and obvious displacement meters. These meters have progressed well over the last 10 years, but can still be prone to poor installation, vibration and zero drift determination errors. Ideal for test bench use where they are enduringly installed, and with right tube models now becoming a norm, they offer low pressure drop and exquisite viscosity rangeability.
(4) Pressure Drop Characterization. An increasingly coarse recipe for obtaining precise measurements without affecting the oil system carrying out due to insertion of flowmeters. Individual parts of the motor oil flow system are instrumented for pressure tapping locations and each motor part is flow characterized on a calibration bench for oil flow against pressure drop at the required temperatures. Once each system has been characterized the motor is reassembled and tested, and the recorded pressure measurements are then used to obtain the flow rate. This recipe is generally used on requisite motor lubrication surveys, where the insertion of a flow meter would have a detrimental succeed on the oil flow system.
(5) Ultrasonic Clamp on meter. Although a non intrusive device, due to its right pipe premise requirements, it does mean the system becomes intrusive into the oil determination system. Still very high-priced to purchase, and presently not sufficiently tested in these applications to come to be a favorable contender, although progressing faster than most other techniques.
Having decided on your recipe of flow measurement, and undertook the required level of flow meter calibration across the range of operating temperatures, you are close to taking a basal step forward in acquiring good flow determination results. Engineers relatively new to motor lubrication studies should seek advice from the Flow Calibration Laboratory, who should be suitably experienced in this type of flow determination application and be in a good position to find the best clarification for your allocation and flowmeter hardware inventory.
Other Issues to bear in mind. The involved nature of motor oil flow determination means it is very difficult to get precise oil flow readings from a running engine, but the informed engineer can make sound engineering judgements on their determination process. Keep in mind the influences of oil viscosity, oil temperature, meter premise succeed on flowmeter and oil pump performance, oil aeration, relief valve effects and hysteresis, fuel dilution effects, motor oil levels, etc. The next series of discussions will delve deeper into the implications of these parameters in more detail.
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