Research in focus

Motors on trial

On the grounds of the Fraunhofer Institute for Building Physics in the Bavarian town of Holzkirchen, there are certain buildings that can only be visited rarely and only after prior approval has been obtained from the responsible departments. The Test Facility for determining evaporative emissions from propulsion systems – or the engine test bench for short – is one such case. This is where German automobile manufacturers such as BMW bring their latest vehicle components and engines for testing by the Building Chemistry, Building Biology, and Hygiene department. Most of the parts tested come from vehicles destined for export, primarily to the North American market. The competitive pressure between vehicle manufacturers is great and therefore the work carried out by Fraunhofer researchers in Holzkirchen is strictly confidential and takes place behind closed doors.

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In the US – and especially in California – the regulations governing vehicle emissions are significantly stricter than in Europe. The government’s objective is to improve air quality and to reduce health risks in urban and suburban areas. Many Americans have their cars parked essentially in their living rooms, as the garage in single-family homes is often separated from the actual living area by nothing more than a plasterboard wall. Once these walls have become saturated with pollutants, they allow close to 100 percent of the car’s harmful emissions to pass into the living areas. This is why the US Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) periodically set the automobile manufacturing sector emission limits for individual substances and substance groups such as nitric oxides, carbon monoxide, formaldehyde, and hydrocarbons, with diesel vehicles additionally subject to limits on particulates. New vehicles are divided into emission groups. These start with so-called low-emission vehicles (LEV) and go all the way down to zero-emission vehicles (ZEV). An expected toughening of the CARB limits in 2017 will further increase the pressure on automakers exporting to California and the US. As things stand, they already have to ensure their vehicles comply with these regulations over a period of 15 years use or 150,000 miles. To be able to meet these requirements over the long term, emission behavior has to be optimized while the vehicle is still under development as well as being subsequently monitored.
When determining and optimizing evaporative emissions, the industry distinguishes between two categories: fuel emissions, which escape when filling fuel tanks or refueling vehicles at filling stations, and non-fuel emissions, which escape into the environment from materials, vehicle components, vehicle assemblies, or drive systems. Ordinarily, the whole vehicle is tested in an emission test chamber – a costly and time-consuming procedure that only takes place once the vehicle is in production. Consequently, faults and issues are detected very late, which in the worst case could cause production of new vehicle series to be stopped.

Fraunhofer IBP offers the major advantage that its scientists are able to test individual parts such as the engine or assemblies separately in smaller test chambers, with volumes ranging from 100 liters up to 7.5 m 3. The measurement data acquired is stored in a database and is available to project partners online around the clock. This means that anomalies can be addressed at an early stage and the test data can be acted on while new vehicle types are still being developed. The objective is to use the measurements to achieve an optimization of parts and components in a process running parallel to the development phase, so that the legal requirements are met by the time the model is launched and goes into series production – and continue to be met throughout the lifetime of the vehicle. The main focus is on testing and evaluating evaporative emissions from volatile organic compounds in the fuel and non-fuel areas.

Performing these extensive measurements over many years has given the Fraunhofer employees a huge wealth of experience, which helps them in their daily work. Since the test bench was commissioned in 2005, testing capacity has increased by 50 percent. Over time, a broad range of tests have detected significant sources of emissions in the area of fuel emissions, for example in relation to seals or unsuitable tube materials. Moreover, we now know that newly developed engines produce high evaporative emission values at the beginning, and that the key to getting these emissions down quickly is through the use of heat. “You can often get big results from the smallest of measures, and achieve lower emissions through the early optimization of components and assemblies,” says IBP scientist Dr. Michael Rampfl as he describes the benefits of his test facility. Examples of such measures include fitting activated carbon filters to increase the absorption of pollutants at certain connections, or manufacturers replacing a connector with a screw connection. “However, you must never lose sight of the cost-benefit ratio, as this is uppermost in the customer’s mind when looking to eliminate the causes of emissions,” explains Rampfl.
Tests on a newly developed engine have shown that engines often do not meet the legal requirements for evaporative emissions of hydrocarbons without optimization measures. Yet a small number of emission-preventing measures were all it took to meet the requirements. Furthermore, the Fraunhofer IBP researchers were pleased to discover that the results of the optimization measures from the vehicle development phase are also being used in series production.

You can find further information in the following article (only German): "Test Facilities for Determining Emissions from Evaporation Processes and Optimizing Emission Behavior under Defined Environmental Conditions"
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