Hybridization may prove to be the most significant way forward for diesel-engine technology, producing very impressive fuel and emissions savings. Competing with gasoline technology improvements and reducing costs will also be a spur to diesel development. Allied to changes that include ever higher pressure common-rail injection systems—reaching around 2400 bar (34.8 ksi), diesel-engine efficiency is set to achieve levels that would, even a few years ago, have generally been regarded as at best unlikely and at worst impossible.
Citroën's new Director General, Frédéric Banzet, speaking to AEI, made it clear that the company, together with Peugeot, was firmly on the diesel hybrid road to very low CO2 emissions figures. PSA Peugeot Citroën’s use of "breakaway" technology is aimed at providing cars that are not just super efficient but will be enjoyable and even entertaining to drive, essential elements if the buying public is to embrace new—and more expensive—environmentally responsible systems.
While downsizing diesels is certainly part of the picture, there comes a limit in terms of cost/benefit ratios, and Banzet felt that, at present, about 1.4-L looked likely to be as small as diesel engine size would go.
It will be Citroën’s sibling, Peugeot, that now looks likely to become the first company in the world to launch a volume production diesel hybrid. Based on the conventional compact/medium PSA Platform 2 five-seat 3008 crossover range, which has a 4365-mm (171.9-in) length, 2613-mm (102.9-in) wheelbase, and 1399-1539 kg (3084-3393 lb) curb mass, it is scheduled for early 2011.
Development work on the car, including extreme weather conditions testing, is now under way, and Peugeot’s hybrid teams are confident that it will reach or better CO2 targets. At present, development vehicles are achieving 109 g/km.
However, a company executive told AEI that this could reduce by some 10% on the production version.
The 3008 Hybrid4 production car will include a diesel particulate emissions filter and stop/start system. Its 2.0-L turbodiesel engine driving the front wheels produces 120 kW (161 hp); a 27-kW (36-hp) electric motor drives the rear wheels. Combined, these sources provide a maximum 300 N·m (221 lb·ft) to the front wheels and 200 N·m (148 lb·ft) to the rear. Fuel consumption is targeted at 4.1 L/100 km.
The architecture of the 3008 Hybrid4 is said to provide four-wheel drive without constriction to engine compartment or interior space. Performance is similar to that of a potential, conventionally powered 2.2-L HDi 3008.
An important element of Peugeot’s stop/start system for diesels is a reversible alternator, sufficiently developed now for the company to have confidence in it as a production component. With an output of some 4 kW, it works as both a starter and alternator, its operation quieter and faster than a conventional alternator. A power electronic control unit, comprising an inverter and converter, is incorporated into the alternator, which controls the system and is linked to the engine’s ECU. The system offers energy recovery.
A problem with diesel hybrid technology is the initial cost, and Peugeot is trying to keep this down by using as many COTS (commercial off-the-shelf) components as possible.
Added weight of the hybrid compared to a regular 3008 is said to be around 100 kg (220 lb). The production car will use a robotized six-speed gearbox, currently an option of the 308 hatchback.
PSA Peugeot Citroën is expected to introduce further diesel hybrid versions if the 3008 Hybrid4 is successful. It is more likely that larger new models would offer ideal platforms for such technology, although so far this has not been confirmed by the company.
While the diesel offers step-change potential for improved fuel consumption and emissions in hybrid configuration, the latest nonhybrid diesels are also achieving impressive levels of efficiency. Interestingly, though, the 4.1 L/100 km fuel consumption potential for the hybrid 2011 five-seat 3008 is that of smaller, conventional diesel cars today.
Within the Volkswagen Group, new 1.6-L TDI engines for Audi and VW models are examples. The Audi A3 with a 77-kW (103-hp) unit has a combined fuel consumption figure of 4.1 L/100 km and CO2 emissions of 109 g/km. The engine benefits from stop/start technology and energy recovery. It will be used in the MY2010 VW Polo.
Diesel engines are now becoming acceptable for roadsters. The Audi TT is already available with a 2.0-L TDI, and significantly, VW’s mid-engine Concept BlueSport roadster study also has a 2.0-L diesel engine with a claimed combined figure of 4.3 L/100 km and 113 g/km. Power output of the engine is 132 kW (177 hp) and 350 N·m (258 lb·ft) is available from 1750 rpm. Theoretical range of the car between refills is 1150 km (715 mi).