The writing may be on the wall for small three-cylinder turbo engines.

Paris, France - Tougher European car emissions tests being introduced in the wake of the Volkswagen scandal are about to bring surprising consequences: bigger engines.

Industry sources say carmakers that have spent a decade shrinking engine capacities to meet emissions goals are now being forced into a costly U-turn as more realistic on-the-road testing exposes deep flaws in their smallest powerplants.

Renault, General Motors and Volkswagen are reportedly preparing to enlarge or scrap some of their best-selling small car engines over the next three years. Other makers are expected to follow, with both diesel and petrol engines affected.

The reversal makes it even harder to meet CO2 targets and will challenge development budgets already stretched by a rush into electric cars and hybrids.

Alain Raposo, head of powertrain at the Renault-Nissan alliance, explained: “The techniques we've used to reduce engine capacities will no longer allow us to meet emissions standards.

“We're reaching the limits of downsizing,” he said at the Paris motor show, which ends on Saturday, while Renault, VW and Opel all declined to comment on specific engine plans.

For years, carmakers kept pace with European Union CO2 goals by shrinking engine capacities, while adding turbochargers to make up lost power. Three-cylinder engines of less than a litre have become common in cars up to VW Golf size, while some Fiat models run on twins.


These mini-motors sailed through official lab tests conducted - until now - on rollers at unrealistically moderate temperatures and speeds. Carmakers, regulators and green groups knew that real-world CO2 and nitrogen oxide emissions were much higher, but the discrepancy remained unresolved.

All that is about to change. Starting in 2017, new models will be subjected to realistic on-the-road testing for NOx, with all cars required to comply by 2019. Fuel consumption and CO2 will follow two years later under a new global test standard.

Independent testing in the wake of Volkswagen’s exposure in 2015 as a US diesel emissions cheat has shed more light on the scale of the problem facing car companies.

Their smallest European engines far exceed legal emissions levels when driven at higher loads than current tests call for. Heat from the souped-up turbos generates diesel NOx up to 15 times over the limit; petrol equivalents lose fuel-efficiency and spew fine particles and carbon monoxide.

Industry analyst with influential forecaster IHS Automotive, Pavan Potluri said: “They might be doing OK in the current European test cycle, but in the real world they are not performing.

“So there's actually a bit of 'upsizing' going on, particularly in diesel.”

In retreat

Carmakers have kept understandably quiet about the scale of the problem or how they plan to address it, but industry sources shared details of a retreat already underway.

GM will not replace its current 1.2-litre diesel when the engines are updated on a new architecture arriving in 2019; the smallest engine in the range will be 25-30 percent bigger.

VW is replacing its 1.4-litre turbodiesel three with a four-cylinder 1.6 for cars such as the Polo,the sources say, while Renault is planning a near-10 percent enlargement to its 1.6-litre R9M diesel, which replaced a 1.9-litre model in 2011.

In real-world driving conditions, Renault’s 900cc H4Bt turbopetrol injects extra fuel to combat overheating, resulting in high emissions of unburned hydrocarbons, fine particles and carbon monoxide.

Cleaning that up with exhaust technology would be too expensive, sources say, so the three-cylinder will be dropped for a larger successor developing more torque at lower revs to stay cool.

The turnaround on size is a European phenomenon, coinciding with diesel's sharp decline in smaller cars. Larger engines prevalent in North America, China and emerging markets still have room to improve real emissions by shrinking.

Inevitable reckoning

Fiat, Renault and Opel have the worst real NOx emissions among the newest “Euro 6” diesels, according to test data from several countries; brokerage Evercore ISI warned in September that they now “face the biggest burden” of compliance costs.

Thomas Weber, head of research and development at Mercedes - which has nothing with less than four cylinders - said such reckonings were the inevitable result of on-the-road testing.

“It becomes apparent that a small engine is not an advantage,” he said. “That's why we didn't jump on the three-cylinder engine trend.”

Analysts predict the tougher tests may kill diesel engines smaller than 1.5 litres and petrol engines below about 1.2, increasing the challenge of meeting CO2 targets and adding urgency to the scramble for electric cars and hybrids.

Volkswagen has been far more vocal about ambitious plans announced in June to sell two to three million electric cars annually by 2025 - about a quarter of its current vehicle production.

Frost & Sullivan analyst Sudeep Kaippalli predicts a hybrids surge.

“You can't downsize beyond a certain point, so the focus is shifting to a combination of solutions,” he said. “In future, downsizing will mean you take a smaller engine and add an electric motor to it.”


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