Hundreds of thousands of car enthusiasts are set to flock to Frankfurt's IAA motor show next week where auto giants hope to show off their electric prowess as scandal-plagued diesels take a backseat.

Two years after "dieselgate" crashed the last IAA party, when Volkswagen's public admission that it had cheated on diesel emissions tests embarrassingly coincided with the fair, organisers are hoping to turn the page by focusing on the cleaner cars of the future.

But as more automakers have come under suspicion and concern about diesel pollution has grown, industry expert Stefan Bratzel expects the mood at this year's 10-day extravaganza to be "mixed".

"On the one hand, the auto industry is enjoying its best years ever in terms of sales and profits, but on the other it's wondering what's going to happen in future," said Bratzel of Germany's Center for Automotive Management.

"Diesel and its harmful emissions are a topic of hot debate right now, especially in Germany, creating an image problem for the entire industry."

German Chancellor Angela Merkel, eyeing a fourth term in a September 24 general election, will on Thursday formally open the 67th International Motor Show, in what promises to be a more politically charged event than in past years.

Dieselgate has wormed its way into the German election campaign as voters fret over the resale value of their cars and over diesel bans mooted by some cities.

While Merkel has said she had been "angered" by the cheating scam, she has also been careful not to demonise a sector that is the backbone of the German economy and employs more than 800,000 people.

"Diesel, and the internal combustion engine, will exist for many, many years to come," she said in a recent interview.

But other countries aren't so sure. Both France and Britain have announced plans to ban the sale of new diesel and petrol cars by 2040 to clamp down on harmful emissions.