Engine Testing and Humidity

Engine testing is an important environmental requirement in the design and production of petrol and diesel engine motor vehicles, trucks, diesel locomotive engines, aircraft engines and gas turbines. Testing is regulated by the Environmental Protection Agency (EPA) and the Californian Air Resources Board (CARB) in the USA and in Europe is covered by various EC legislative standards.

Typical emissions that are monitored include NO, NO2, N2O4, SO2, SO3, CO, CO2, Pb and residual hydrocarbons. The relative concentrations of these emissions are affected by various factors, including ambient temperature, pressure and humidity and the type of engine, fuel and conditions of use. It follows therefore that in order to minimise variability of test results, extraneous factors need to be controlled or eliminated wherever possible.

Studies carried out in the USA by the Environmental Protection Agency (C D Paulsell, Moisture and Humidity, 1985: pp 735-744, Instrument Society of America) illustrated that the most successful method of determining the ambient humidity for the correction of the emissions concentrations was to use a cooled mirror dewpoint hygrometer. Paulsell's research showed that other instruments were extremely prone to errors in measurement due to a wide variety of factors and, even if used under carefully controlled conditions, had no significant advantages over the use of a cooled mirror dewpointmeter.

Michell's OPTIDEW, DEWMET and S4000 Precision Cooled Mirror Dewpointmeters are all ideal products for this application. They offer accurate and continuous measurement (within ±0.2°C dewpoint) of the ambient dewpoint in an engine test cell and perhaps more importantly, are capable of extended service without drift and with full confidence. Every instrument is delivered fully calibrated, traceable to national standards - we maintain direct traceability to NPL (London, UK) and NIST (Washington DC, USA) through our UKAS accredited Humidity Calibration Laboratory. This satisfies the most stringent of quality system requirements and gives ultimate confidence in the measurement being made.

The above notes relate specifically to emissions in motor vehicle testing. Similar applications apply in truck, locomotive and aero testing for similar reasons. In the particular case of aero engine testing the analysis is more targeted to obtaining optimum performance from the aero engine rather than to minimising emissions. In all of these applications Michell's Cooled Mirror Dewpointmeters have been successfully used by numerous World famous organisations.

Household names feature among Michell Instruments' customers, including Ford, Saab, Skania, Jaguar Rolls Royce, MIRA, Cosworth Racing, Volvo. These customers are just a sample of the many hundreds that use products from Michell Instruments to solve the problems they experience with moisture in gases.

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