FRANKFURT -- Scandals. Recalls. Threats of bans. The diesel engine is a public enemy for many environmental activists and politicians.

And yet, when the world's biggest automakers unveil new models at this year's auto show in Frankfurt, among the new electric vehicles and digitally-enhanced prototypes there will also be diesel cars.

The carmakers at the show, mainly Germany's big manufacturers, are hoping to modify diesel engines to make them cleaner rather than throw them out altogether. It's a bid for stability in an industry roiled by change.

Here's a quick look at the major themes and vehicles expected at the Frankfurt International Motor Show, which opens for journalists Tuesday and Wednesday and to the general public from Saturday through Sept. 24.

DIESEL DILEMMA

German carmakers, which have relied heavily on diesel, have been bruised by controversy over the technology since Volkswagen's scandal, in which the company admitted to illegally rigging cars to turn off diesel emission controls when not on test stands. Subsequent investigation found that many diesels by other manufacturers met official test standards but emitted far more pollution during every day driving, often by exploiting legal loopholes that permitted them to turn off controls at certain temperatures. German carmakers are recalling some 5 million older diesel vehicles to tweak their engine control software in hopes of warding off pressure for diesel bans in some cities.

So expect a lot of emphasis on emissions-free technology such as battery-powered cars. Daimler will show off a fully electric, compact car under its EQ brand, which represents the company's push into areas it has bundled under the acronym CASE: connected, autonomous, shared and services, and electric.

It also will unveil the Mercedes-Benz GLC F-Cell, a fuel-cell and battery plug-in hybrid that emits only water vapour. Fuel cell-powered cars are not yet a practical option for consumers, with only 33 hydrogen fuel stations in Germany, but it's one possibility for the future in which government regulation will increasingly require low-emission vehicles.

DIESEL DESPITE THAT

But diesel remains in the mix --with what automakers say are better emissions controls to meet European Union standards in which cars will be tested under real-world driving conditions, as well as on test stands. Diesels get better mileage -- a big consumer issue in Europe, where fuel taxes make gasoline painfully expensive. A litre of gasoline costs 1.31 euros in Frankfurt, or $5.97 a gallon. And diesels emit less carbon dioxide, meaning they help meet regulatory limits on the greenhouse gas believed to contribute to global warming. The new T-Roc small SUV from Volkswagen, for instance, will come with three possible gasoline engines to choose from -- and three diesels. Automakers "won't be shouting about it, but diesels will be part of their lineup," says Ian Fletcher, principal analyst at IHS Market.

IHS estimates diesel's market share will fall from 49.7 per cent in Europe to 46.9 per cent this year, and to 32.8 per cent by 2025.

Mercedes-Benz spent 3 billion euros to develop new diesels, which are already being used in its E-Class sedans.

THE HOME TEAM

Increasingly, carmakers are finding other ways to unveil new models than auto shows and that has become even more evident ahead of this year's show. Volkswagen's Porsche brand showed off its new Cayenne SUV at an extravagant event Aug. 29 with the Bohemian Symphony Orchestra Prague and dancers livestreamed from its home base in Stuttgart-Zuffenhausen. Automakers skipping the show this year include Fiat Chrysler's namesake Fiat and its Jeep and Alfa Romeo brands, Peugeot and its DS luxury division, plus Nissan, Infiniti and Volvo.

Yet the Frankfurt show remains a very big deal for the home team: Daimler AG's Mercedes-Benz luxury brand, Munich-based BMW AG, and Volkswagen, all of which will have giant display stands. Some 1,000 exhibitors will show off 300 premieres on 200,000 square meters of space. Chinese brands WEY and Chery will exhibit for the first time.

DIGITAL AND ELECTRIC DISRUPTION

Automakers will be eager to show off technologies that can help people get around without owning a car. That could include ordering rides through an app, sharing someone else's car for a price, and autonomous vehicles.

Facebook COO Sheryl Sandberg, will speak at the opening ceremony, while Google is a sponsor for the media night. Computer security company Kaspersky Labs and AVL Software and Functions GmbH are showing off a product to protect cars from hackers. Daimler announced Wednesday it was investing in peer-to-peer car sharing company Turo and said it plans to fold its own car sharing pilot project, Munich-based Croove, ahead of Turo's entrance into the German market in 2018.

HOT PRODUCT

The main reason to hold an auto show, of course, is to show off autos. Some of the models attracting the most industry attention will include: Audi's A8 four-door sedan with an eight-speed transmission and all-wheel drive; the eighth generation of the Rolls-Royce Phantom; and a new version of Volkswagen's Polo compact, which comes in gasoline and, yes, diesel versions.

Small SUVs remain a popular category for new vehicles. Car buyers like the higher seating position, while carmakers save development costs by putting a new body style on top of mechanical components they've already paid to develop for compact cars. They include: the SEAT Arona, Jaguar E-Pace, Kia Stonic, Citroen C3 Aircross, Skoda Karoq, and a so-far unnamed offering from Chery.

HYPERCARS

It wouldn't be an auto show without freaky fast, completely unaffordable supercars to gawk at. Daimler has the Mercedes-Benz-AMG Project ONE, a two-seat hybrid with over 1,000 horsepower and a top speed of 350 kph (217 mph.) A teaser photo shows the silhouette of a car with a low silhouette and big wheel wells.