Radical real-world fuel consumption tests will force car-makers to completely rethink their engine downsizing culture, says a new report.
According to newswire Reuters, new fuel consumption tests -- introduced in part as a knee-jerk reaction to Volkswagen's Dieselgate emissions crisis -- no longer favour the small-capacity turbocharged three- and four-cylinder petrol and diesels many car-makers have developed.
Reuters says the problem is that where the small engines performed excellently in the old laboratory tests, the new real-world tests uncover higher levels of both CO2 and NOx because of increased use of the turbo.
Other problems highlighted by the new tests are small engines overheating during evaluation. This then sees the engine's ECU trigger the cooling system or a program of over-fuelling the engine, resulting in more fuel being used and unburnt hydrocarbons and particulates exiting the exhaust, increasing emissions further.
Speaking to Reuters, IHS Automotive analyst Pavan Potluri said small-capacity engines "might be doing OK in the current European test cycle, but in the real world, they are not performing".
Reuters says some car-makers like General Motors' European brand, Opel, have already reacted by phasing out its 1.2-litre diesel for a bigger 1.5-litre that will be introduced in 2019.
The newswire also claims Volkswagen is in the process of replacing its downsized 1.4-litre three-cylinder diesels with larger 1.6-litre four-cylinder engines. Renault too, in the future, is claimed to already be working on a larger-capacity entry-level diesel engine.
Speaking to Reuters, Renault's head of powertrain Alain Raposo said that car-makers were "reaching the limits of downsizing".
"The techniques we've used to reduce engine capacities will no longer allow us to meet emissions standards," said Raposo.
Volkswagen will next month reveal an upgraded Golf that's set to introduce a new range of 48-volt mild-hybrid powertrains based around a tiny turbocharged 1.0-litre engine. If the new engine doesn't deliver in the real-world tests it could cost the German car-maker billions.
In future all diesel engines below 1.5 litres and all petrol engines smaller than 1.2 litre will be rendered obsolete, says the Reuters report.
Thomas Weber, head of R&D at Mercedes-Benz, told the newswire that the disadvantages of downsizing, in the real world, have been long known.
"It becomes apparent that a small engine is not an advantage," Weber told Reuters. "That's why we didn't jump on the three-cylinder engine trend."
According to industry experts, further downsizing is expected to be abandoned in the future and replaced by increased hybridisation.