Contact-free Measurement of Combustion Air on Engine Test Benches

28. August 2017 | Software & Testing Solutions

Significantly increased requirements regarding the environmental compatibility of combustion engines require more specific measures for reductions in consumption and emissions. Every modification to the engine must be examined on a test bench with regard to its impact on emissions and fuel consumption, among other things. In this context, the exact measurement of the combustion air mass flow is very important. For this purpose, FEV has developed the FEV AirRate, which is now available in an improved and completely redesigned version. The AirRate is used for the contactless measurement of gas velocity, pressure, humidity, and temperature of the combustion air on engine test benches. The air mass flow in kg/h is calculated and displayed using these parameters.

High Measurement Accuracy

The ultrasonic gas flow meter with 8 ultrasonic transducers in 4 measurement paths enables very high accuracy in measurement throughout the entire measurement area. The extremely fast response time of the system ensures reproducible air quantity measurements, even for highly dynamic processes in the induction tract. Due to the low pressure loss in the AirRate measurement section, engine behavior is not affected. Due to the large measurement range spread of the AirRate 100 and AirRate 150 measurement systems, the complete range, from single cylinder engines to heavy duty engines, can be covered with only 2 device sizes.

Compact Design in a Single Casing

The AirRate requires very little space; thanks to the compact design, the entire measurement technology fits in a single casing, and there is no need for wiring between the measuring unit and the output unit.

The flow rectifiers integrated in the device effectively reduce turbulence in the combustion air, thereby enabling the system, for example, to be installed directly behind a pipe elbow without any extension of the inflow section whatsoever. Integration in test benches, with or without combustion air conditioning, is thus very easy, as is a quick conversion for operation with or without AirRate.

Clear Operation

During the redesign, special attention was paid to an increase in measurement frequency and simple and clear operation.

Compared to the previous device, the measurement frequency has more than doubled; in addition to pressure and temperature measurements, a humidity measurement has been added for mass determination. The four-path design with a total of eight titanium ultrasonic sensors guarantees very high accuracy in measurement, even under difficult flow conditions. In addition, a plausibility check is carried out between the paths, so that the drift of a path can be detected and reported. Due to the path compensation functionality, the malfunction of an entire path can be compensated for by the device, with no loss of measurement accuracy.

The AirRate is operated via the 7” touchscreen display with easily readable graphic elements, via the web browser, or via the WiFi interface. The latter in particular enables very easy operation and settings adjustments – even in difficult and inaccessible installation conditions – through the use of a smartphone, for example.

All settings are password protected; as a result, any unauthorized or accidental incorrect adjustment of the settings is excluded. The operation surface and the web menus are available in several languages and can be expanded by the user.

Low Maintenance and Calibration Requirements

In addition to the power output (4 to 20 mA), a tension output is now also available (0 to 10 V). The series interface with the AK protocol is fully compatible with the previous version. A simple replacement is therefore possible, since the mechanical connection dimensions were maintained. The AK protocol is also available via TCP/IP in addition to the series interface.

The pressure, temperature, and humidity sensors all communicate via a digital bus protocol. This enables them to be easily replaced by factory-calibrated spare parts in case of a defect; a recalibration of the device is not necessary in this case.

The calibration interval of the AirRate is 2 years and is therefore significantly better than comparable hot film measuring devices with a 6-month calibration interval. Upon request, a DAkkS calibration of the AirRate is possible.