Engine testing

The MAHLE location in Muskegon, MI.

Testing engine components in the engine is an indispensable part of engine development. In-house engine tests provide incontrovertible facts about the function and quality of the products.

The MAHLE Group maintains thirteen Tech Centers with eight engine testing facilities, with a total capacity of 92 test benches. The Tech Centers, and therefore the engine test labs, are located near the most important development centers of the automotive industry, thus allowing close cooperation with customers on location.

Development and testing of engines and their components are increasingly decentralized. Transparency and exchange of information among the various engine testing locations are therefore indispensable.

The MAHLE engine testing locations are networked via global databases and work platforms. This means that technical data are available locally at any time and the regular exchange of information and experiences is guaranteed. Strategies for engine testing, measurement and analysis methods, and test programs are discussed and compared during regular meetings.

MAHLE engine testing involves a variety of tasks that can be essentially divided into six areas.

  • Measurement method development
    New measurement, testing, and analysis methods provide important information for new product development. Following global coordination and local development, new methods are rolled out globally within the MAHLE Group. This means that new methods can be implemented at all locations, providing valuable data and facts both within MAHLE and for customers.
  • Fundamental research
    This includes preparing and verifying generally applicable catalogs of actions for special problems and subject areas.
  • Engine testing of new products
    Before new products are released for customer applications, they must meet a high degree of technical maturity and functionality. New products are therefore tested and validated internally in engine test runs.
  • Engine testing of products through to series production release
    In the course of product development, existing products are adapted to the customer’s specifications and tested in customer-specific engine test runs. Holistic testing of a power cell unit (PCU, including pistons, piston rings, and cylinder liners) is indispensable for assessing the interactions between individual components and harmonizing them with each other.
  • Troubleshooting
    Complications with series production products require prompt response. Field failures must be reproduced with appropriate test runs in the engine testing facility so that potential remedial measures can be tested.
  • Development services
    Engine testing can provide the customer with extensive assistance based on experience and technical expertise, performing a wide range of engine tests as a development services provider.

Engine testing is one of the final steps of development for any product. Only actual engine operation can show the true operating behavior of components and potential interactions with other components. Detailed optimization measures for achieving the primary development objectives listed below cannot be implemented prior to engine testing, nor can their effectiveness be demonstrated.

  • Verification of functionality and component strength
  • Optimization of oil consumption and oil separation
  • Preventing oil carbon build-up and deposits of various residues
  • Optimization of component cooling and temperature distribution
  • Optimization of acoustics and vibration behavior
  • Optimization of flow systems
  • Minimizing frictional losses and component wear
  • Analysis of thermodynamic and emissions behavior
  • Operating map application and data population.

MAHLE engine test benches can run units ranging from small two-stroke engines to gasoline and diesel passenger car engines to heavy commercial vehicle engines. The test benches cover a range of power outputs of up to 1,200 kW.

Modern test bench automation systems are now the state of the art and allow unmonitored engine operation around the clock. Complex logistics tools for planning test sequences and quick changeout systems shorten engine setup times on the test benches, substantially increasing their utilization rate and avoiding unnecessary idle times.

In addition to a number of mechanical development and functional test benches, as well as test benches for thermodynamic and emissions analysis, MAHLE operates various specialized test benches on which additional key development areas can be addressed, such as frictional losses, acoustics, and cold starts.

Mechanical development and functional test benches

All engine operating media are conditioned by the test bench for mechanical development, functional verification, and component strength testing in long-term testing. Active test bench brakes allow driven engine operation, so that commercial vehicle engine braking systems can also be tested, for example.

In addition to specific MAHLE test programs, all customer-specific test runs (e.g., thermal shock tests) can be performed.

Thermodynamic test benches

In addition to the test bench conditioning systems for mechanical development and functional test benches, thermodynamic test benches are equipped with intake air conditioning systems. High- and low-pressure indexing systems and corresponding analysis tools are available for thermodynamic tests. For analyzing exhaust gas components, FTIR (Fourier Transform Infrared Spectrometer) systems are available, in addition to the typical five-component analysis. A number of measuring instruments are also used for analyzing particle mass or particle count in the exhaust gases.

Cold test bench

Cold test benches

The cold test bench allows the cold start behavior of the engine to be evaluated and diverse surface coatings to be tested with respect to damage due to cold start scuffing. The entire test bench, including the coolant, oil, and intake air temperatures, can be cooled down to –28°C.

Acoustic test bench

Acoustic test benches

Low-reflection test benches are used for extensive NVH (Noise, Vibration, Harshness) tests for optimizing the acoustic behavior of components, such as pistons, bearings, valve train components, and intake modules. Both structure-borne and airborne noise measurements can be taken. Defined test runs can precisely reproduce noise excitation on the test bench, allowing the objective comparison of potential remedial measures.

Friction power test bench for complete engines

Friction power test benches

An important contributing factor for reducing CO2 is the minimization of frictional losses in the engine. In addition to simulation and determining frictional coefficients outside of the engine, MAHLE uses several engine measurement methods for determining and minimizing frictional losses.

The friction forces of the pistons, piston rings, and cylinder group can be determined as a function of degrees of crank angle in a single-cylinder floating-liner engine, by measuring the axial forces acting on the cylinder liner.

With the friction power test bench for complete engines, MAHLE uses a tool that determines mean friction pressure operating maps using the indication method on a driven, live complete engine. A wide range of design parameter variations thus allows measures to be compared over the entire operating map. Using the mean friction pressure operating map, suitable simulation tools can be used to calculate CO2 emissions in customer-relevant driving cycles.

Customer engines can thus be optimized individually with respect to CO2 emissions in legally relevant driving cycles as well.

Coolant surface of a cylinder liner damaged by cavitation


Cavitation, especially on wet cylinder liners in large commercial vehicle engines, can cause pitting corrosion on the cylinder liner and therefore lead to engine failure after long running periods. The effectiveness of remedial measures must usually be demonstrated in long, high-cost durability runs.

Micrograph of a cylinder liner damaged by cavitation

MAHLE has developed a complex measurement method and an analysis methodology that allow cavitation propensity to be diagnosed and analyzed.
The effectiveness of remedial measures can thus be demonstrated at a low cost and in a short time.

Stationary oil consumption characterization map

Oil consumption

In addition to conventional gravimetric methods, such as the weighing method or the volumetric method, or measuring the oil level in the pan to determine oil consumption, MAHLE also uses analytical chemical methods. Methods using tracers such as sulfur or tritium are also used, as are tracer-free analytical chemical methods.

Oil consumption in a dynamic test run

The use of mass spectrometry to determine oil consumption is such a tracer-free analytical chemical method that is gaining in significance. The method provides a great deal of information within a very short time. Static oil consumption characterization maps can thus be created within a few hours. Thanks to continuous measurement of oil concentration in the exhaust gas, it is possible to determine oil consumption in transient operating conditions. The responsiveness of the measurement system is fast enough to evaluate even highly dynamic oil consumption effects, such as rapid cycling of loads and speeds. Extracting the exhaust gas directly after the combustion chamber allows selective measurements to be made for each cylinder.

Extensive studies have produced catalogs of measures that can be used for targeted oil consumption optimization.

Piston temperature

For reliable piston service life calculations, it is absolutely necessary to determine the piston component temperature. Depending on the requirements, various measurement methods are used to assess component temperatures.

One fast, simple measurement method is the use of a templug (steel screws made of a defined alloy) to determine the piston temperature at a steady-state operating point. The residual hardness and application time of the templug can be used to calculate the maximum temperature of a component.

Passenger car piston subjected to NTC metrology

The measurement method known as NTC is used for higher requirements. Semiconductors known as NTCs are used as measuring sensors. Data is transferred contact-free, using inductive coupling, to an external data acquisition and analysis unit. A maximum of three measurement points can be applied to each piston.

For the highest requirements—i.e., for extensive measurements over the entire operating map, parameter variations, and transient measurements in customer-specific test runs—the system known as RTM (Real-time Telemetry Piston Temperature Measurement System) is used. In this case, component temperatures are measured by means of NiCr-Ni thermocouples. The analog voltage signal from the measurement sensors is modulated into a digital signal by a sensor signal amplifier mounted on the piston. Telemetry is used to transmit the modulated signal wirelessly to an external data acquisition and analysis unit. Up to seven measurement points can be attached to one piston.

Customers can use this real-time measurement method on site at MAHLE to design the combustion application so that the maximum permissible thermal loads for the component are not exceeded.

Passenger car piston with knock damage


Knocking combustion faults in gasoline engines can lead to damage on the piston, or even to engine failure. Using a measurement and analysis method developed at MAHLE, each individual knocking event can be detected and quantified, while the knocking intensity is determined in real time. Comparing knock amplitudes and ignition angle allows conclusions to be drawn about knock controls, thus enabling optimization and verification of knock control systems.