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Putting engines through their paces

02 February 2018

FPT Motorenforschung develops engines destined for the vehicles and machinery of CNH Industrial’s Powertrain segment. Some 220 staff work on site to create new FPT products for commercial vehicles, construction equipment and agricultural machinery and for use in industrial and marine applications.

The engines are put through their paces on a total of 30 test benches. To measure their efficiency, FPT Motorenforschung uses tools such as the Series M5 pressure transmitters from KELLER AG.

The M5 – a design that incorporates technical research requirements 

FPT Motorenforschung’s development work focuses primarily on reducing exhaust emissions and achieving a high power density, low fuel consumption, a long service life and maximum reliability. An engine’s efficiency depends largely on the extent to which the flow of air into and back out of the combustion chamber and that of the exhaust gases is unimpeded. The pressure here will be under 10 bar. The main priority is to get extremely accurate and highly dynamic measurements using absolute sensors. KELLER developed its M5 series to meet these specific engine testing requirements and several of these devices are used at various places on the engine during tests. To obtain a reliable analysis of pressure conditions and losses, it is important to take measurements as close as possible to the individual cylinders on the inlet side. The varying geometry of the intake manifold poses an additional challenge as it means that each cylinder is supplied with a different amount of air, something that has to be avoided as much as possible. On the outlet side, too, the combustion gases in the individual cylinders can cause unwanted interactions between pressure surges or pulses. The pressure sensors measure these processes on the inlet and outlet sides locally and with a high level of phase fidelity. 

When testing engines, it is important for the sensors not to be sensitive to structure-borne noise as the sounds and vibrations from the engine cannot be allowed to interfere with the measurements. The measuring slot should be sealable with a plug once measurements have been taken and should be as resistant as possible to air flows. This application can also lead to compensating currents of up to 40 A being generated by the engine battery – these must not be allowed to influence the sensor. These requirements were met in full when the M5 sensor was developed. Other characteristics of the pressure transmitter also give it an edge in this specific field of use: no bonding wires are needed in the vicinity of the medium, while there are also no connectors between the sensor and the electronic system. This removes any additional contact resistances and sources of faults. The cable gland is hermetically sealed (IP67) to minimise external influences on the cable. Most of the electronic system is fitted externally, enabling it to be positioned in a noise free area.

The M5 series – ultra-fast miniature pressure transducers 

The pressure sensors in the M5 HB series deliver fast and precise measurements to an accuracy of 0.1% FS (full-scale) up to 180°C. The pressure connection to the M5 fine thread is designed for both static and dynamic measurements such as pressure pulses. Their miniature size makes these sensors ideal for local measurements. The sensor’s main attributes are its very low dead volume and its good venting capability. It uses a rear-side technology without a transfer medium that also helps to minimise the attenuation of the measurement signal. No sealants, adhesives or capillaries are needed either.

To prevent any unnecessary impact on flow conditions, the process connection should be as short as possible and, in terms of handling, able to be installed easily even in narrow tubes. The sensor is thus also very lightweight and able to withstand rapid acceleration. The M5 series is available with or without an electronic system. The KELLER team’s top priority when developing its electronic system was signal fidelity up to the limit frequency of 50kHz. The M5 HB pressure transmitters (i.e. with an electronic system) were optimised in line with FPT Motorenforschung’s technical specifications and have been in use for over two years now.

A wide range of potential uses in engine research 

FPT Motorenforschung uses M5 sensors with electronic systems on all of its engine test benches. The company takes measurements inside components such as oil, fuel and water pumps, injector lines, intercoolers, heat exchangers and intake and exhaust ducts. Logging the pressure conditions enables any fluctuations, peaks or other generally unusual pressure phenomena to be detected. The engineers can then use these values as a basis for reworking the design, further optimising the components and parameters of the ECU (the control unit). 

The data obtained makes it easier to extrapolate the dynamic conditions inside the engines. For instance, a pressure loss of 1 Pa at a volume flow of 1m3/s – typical values for the intake air volumes of large HGV engines – translates into 1W of lost performance. In practice, this means that a 50 mbar fall in pressure results in a flow loss of as much as 5kW. Consequently, this value must be kept as low as possible to make the engine more efficient. M5 sensors can also be used in the return pipes in injectors. Because of how they are designed, injectors generate a return flow through leaking and cooling. The pressure conditions in these pipes are also measured and optimised, with the pressure range being from 1 to 5 bar. Oil pressure is a further critical factor in engine efficiency. Whereas it is usually too low in engines running at low speeds, it tends to be too high at high speeds.

“As far as measuring oil pressure was concerned, it was particularly important to find a sensor that was small enough. This is because smaller sensors have less of an impact on the actual flow conditions. Also, there is often very little space to install them with this kind of application, meaning that a standard sensor was never going to be an option. The M5 sensor ticks all the boxes. One particular benefit is the fact that, after testing is complete, the openings for the sensors can be sealed using a simple M5 plug almost as if nothing had changed. This means that any modifications to the system won’t distort the results of other tests,” concludes Rainer Linsenmeyer, Head of Test Engineering/Electronic Measurement at FPT Motorenforschung.

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