Cold comfort

Car engines could be completely wrapped in plastic to improve their fuel efficiency, reduce cold starts and cut emissions.

Car engines could be completely wrapped in plastic to improve their fuel efficiency.

Plastics are finding niches in more and more car parts, from the interior to functional components such as the fuel tank, but the engine compartment is still largely the preserve of metals.

However, researchers at BASF’s polyurethanes subsidiary, Elastogran, are working on plans that could see engines enclosed almost completely in a custom-designed casing of polyurethane (PU) foam.

The casing of moulded, expanded foam blocks will slow down the cooling of the engine after it is switched off, said Bernhard Rosenau, business manager for the European automotive specialities unit for Elastogran. This will reduce the number of cold starts the engine has to undergo, which will in turn improve fuelefficiency and reduce vehicle emissions, he said.

Cold starts represent an engine’s hardest work. It takes almost 10 minutes for the coolant to reach its optimum working temperature, twice that amount of time for the engine oil, and even longer for the gear oil. Up to this point, the engine is operating well below its optimum efficiency.

If the heat can be kept inside the engine, the performance should be nearer optimum for longer.

Reducing heat dissipation from 0.012kW per kelvin, the level for a normal engine, down to 0.002kW/k by adding extra insulation, can cut fuel consumption by 5 per cent during the summer and 9-10 per cent in winter, said Rosenau.

PU is already widely used in the car industry. It is a very efficient insulator and extremely temperature-resistant, and is also easy and cheap to mould, said Rosenau. Foam blocks around 30mm thick can produce the insulation rates required, he said. ‘This figure corresponds to complete encapsulation, apart from the exhaust system and the engine mounting bracket, since encapsulation of the latter would pose major problems.’

The exhaust system, which is much hotter than the rest of the engine, would instead be protected by mineral insulation packed into a metal housing.

The system has been tested at the Cologne University of Applied Sciences, using a 1.4litre VW Golf engine enclosed in a box made from 30mm thick PU foam boards.

The research team, under Professor Norbert Deussen, ran the engine until it had reached its operating temperature of around 100 degrees C, then turned it off and monitored how it cooled.

Although the exhaust gas temperature quickly dropped from almost 500 degrees C to the level of the surroundings, the engine block itself cooled much more slowly – 14-15 hours later it had only dropped to around 50 degrees C. Without the insulation, it reached this level in about two hours. Encapsulation also increases comfort levels in the cabin, according to Rosenau.

On cold days, an insulated engine, retaining its warmth, helps the cabin air reach a comfortable temperature of 23 degrees C far sooner than if the engine is cold, while it also speeds up windscreen de-icing and prevents window fogging.

Deussen’s team has worked with BASF to design a PU capsule to enclose an engine for a production car. Other parts of the engine would also have to be redesigned, he said, as the alternator and gearbox are encapsulated, so they need to be included in the coolant circuit.

‘Thermal engine encapsulation (TEE) must be taken into account even at the vehicle design stage,’ said Rosenau. ‘The retrofitting of existing vehicles is out of thequestion.’

Elastogran is currently working with the Cologne team to investigate whether the financial and environmental benefits of the technique justify the increase in manufacturing and maintenance costs.

The company is also involved in ‘detailed discussions’ on TEE with several German car makers at the top end of the market, Rosenau said, and is working towards building a test vehicle to confirm the experimental results, and to see how the system performs in actual driving conditions.