| One of the most difficult flow measurements for the | | | | manufacturers only provide a calibration certificate on |
| automotive engineer is to measure the engine oil flow | | | | water, which can lead to extremely large errors if |
| rate under operating conditions. With the engine | | | | used on engine oils. |
| mounted on a test bench and coupled to a | | | | (3) Coriolis meters. Very good high accuracy meters, |
| dynamometer, the job is slightly easier due to the | | | | that would only be suited to fixed installations. These |
| increased space availability, but none the less, careful | | | | meters remain highly expensive and are large in size, |
| selection and installation of the flow measurement | | | | compared to the turbine and positive displacement |
| system is required. Flow measurements required in | | | | meters. These meters have progressed well over the |
| the engine bay of a vehicle become further | | | | last 10 years, but can still be prone to poor |
| restricted due to instrument power requirement, | | | | installation, vibration and zero drift measurement |
| installation space required and the harsh under bonnet | | | | errors. Ideal for test bench use where they are |
| conditions. | | | | permanently installed, and with straight tube models |
| What are the flowmeter options? Well, industry | | | | now becoming a norm, they offer low pressure drop |
| standards seem to exist to some extent, but this | | | | and excellent viscosity rangeability. |
| does not mean they are correct. Let us look at some | | | | (4) Pressure Drop Characterization. An increasingly |
| options. | | | | common method for obtaining accurate |
| (1) The positive displacement meter, this could be in | | | | measurements without affecting the oil system |
| the form of a gear meter, piston meter or helical | | | | performance due to insertion of flowmeters. |
| screw to name a few. These meters are generally | | | | Individual parts of the engine oil flow system are |
| on the higher cost side and can cause issues when | | | | instrumented for pressure tapping locations and each |
| installed due to their relatively high pressure drop. | | | | engine part is flow characterized on a calibration |
| Although quite good at operating across wide | | | | bench for oil flow against pressure drop at the |
| viscosities they do suffer from meter slippage at low | | | | required temperatures. Once each system has been |
| viscosities. Meters vary in size, but can often be | | | | characterized the engine is reassembled and tested, |
| installed without the need for any flow conditioning. | | | | and the recorded pressure measurements are then |
| Used by some engine test houses but not an ideal | | | | used to derive the flow rate. This method is generally |
| solution. | | | | used on critical engine lubrication surveys, where the |
| (2) Turbine flow meter, generally one of the most | | | | insertion of a flow meter would have a detrimental |
| widely used flowmeters for engine oil flow | | | | effect on the oil flow system. |
| measurement, mainly due to its low costs and small | | | | (5) Ultrasonic Clamp on meter. Although a non |
| size. They can be purchased relatively easily from a | | | | intrusive device, due to its straight pipe installation |
| host of manufacturers and have a manageable | | | | requirements, it does mean the system becomes |
| pressure drop which is not too detrimental to oil | | | | intrusive into the oil measurement system. Still highly |
| system performance. They are sensitive to oil and | | | | expensive to purchase, and presently not sufficiently |
| fluid flow profile effects, so it is extremely important | | | | tested in these applications to become a suitable |
| to calibrate the flow meter across the varying oil | | | | contender, although progressing faster than most |
| viscosity range and with its installed upstream and | | | | other techniques. |
| downstream flow conditioning tubes. To ensure | | | | Having decided on your method of flow |
| accurate results when in use, it is essential to match | | | | measurement, and undertook the required level of |
| the installed conditions as close as possible. Quite | | | | flow meter calibration across the range of operating |
| often specialist flow calibration laboratories will | | | | temperatures, you are close to taking a fundamental |
| calibrate the flow meter on the same engine oil, at | | | | step forward in acquiring good flow measurement |
| the same operating temperature and with the same | | | | results. Engineers relatively new to engine lubrication |
| inlet and outlet connections as per the installed | | | | studies should seek advice from the Flow Calibration |
| engine. Sometimes this may be part of the engine | | | | Laboratory, who should be suitably experienced in |
| assembly, such as an oil cooler or oil filter assembly, | | | | this type of flow measurement application and be in |
| generally the easiest part of the engine where the oil | | | | a good position to find the best solution for your |
| flow can be interrupted. Many flow meter | | | | budget and flowmeter hardware inventory. |