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Source: Race Engine Technology

Publication Date: 3^rd October 2007

Seat made history at Oschersleben, Germany on August 26 by using diesel power to win a World Touring Car Championship race. Seat is a fellow member of the Volkswagen Group with Audi. The current Super 2000 regulations, to which the WTCC is run, permit the use of a 2.0 litre I4 turbodiesel engine that in effect can be essentially one third of a contemporary Le Mans power plant, such as the Audi R10’s 5.5 litre V12 turbo-diesel. Super 2000 regulations are far more liberal than those of Group N, to which earlier this year Triple Eight and Sodemo co-developed a 1.9 litre turbo-diesel Vauxhall Astra for rallying (see below).

The Seat Leon FR 2.0 TDI, upon which the history-making WTCC car is based uses a double overhead camshaft, 16 valve 2.0 litre turbo-diesel I4 that is employed also by various Volkswagen and Audi models. The output of this 81 mm bore, high-pressure common rail (TDI) injected road car engine is 170 bhp at 4200 rpm. The going rate for Super 2000 petrol engines is approaching 300 bhp, which emphasis the fact that the successful WTCC turbo-diesel engine cannot simply be a straightforward ‘tune up’ of the production unit.

By regulation the WTCC engine has to retain the production block and head. Neither compression ratio nor plenum pressure are restricted (although the former must be at least 16:1). Production iron block turbo-diesel engines such as the Volkswagen Group 2.0 TDI are designed to withstand a plenum pressure approaching the 2.94 bar maximum Audi is permitted to use at Le Mans. We believe that the Audi R10 V12’s compression ratio is no more than 18:1, which is again within current 2.0 TDI production engine parameters.

At the heart of the Audi R10 V12 is a production-style bowl in crown combustion chamber and the bore size is derived from that of an Audi road going turbo-diesel – we believe that it is 83 mm but it could well be the confirmed 81 mm of the WTCC engine. The Super 2000 regulations for diesel engines (‘Diesel 2000’) permit the head to be modified while the rotating and reciprocating components can be bespoke items. Valve lift cannot be more than 10 mm but we understand that the R10 uses less than that figure. A high-pressure direct injection system such as that the R10 exploits may be used and although the turbocharger cannot be bespoke any suitable production unit may be selected. The road car type gas recirculation system may be removed.

The biggest compromise for the WTCC engine is a mandatory wet sump.On the whole the scope exists to transfer the technology of the LMP1 turbo-diesel straight across to Diesel 2000. It seems fair to assume that the Audi Sport Le Mans and Seat Sport WTCC engines operate at comparable compression ratio and boost level – significantly more would tax the Seat’s production base; any less would leave it with insufficient horsepower. Seat Sport engineering chief Benoit Bagur tells us “the (mandatory) 35 mm diameter intake air restrictor limits the pressure we use at high revs. We use less pressure at high revs compared to the ACO maximum limit.”

In the case of both Volkswagen Group fielded turbo-diesel racing engines maximum power is made at 4000 rpm, maximum torque at 2500 rpm. Both operate on the track normally in the range 3000-5000 rpm. Not only is the operating speed range is the same, bore size and stroke are comparable so per-cylinder friction is comparable and when it comes to horsepower output it would clearly be unrealistic to assume that what is in effect one third of the R10 V12 benefits from significantly less percentage frictional loss overall.

The permitted air intake areas are 2500 mm2 for the 5.5 litre Le Mans turbo-diesel and 962 mm2 for the 2.0 litre Diesel 2000 engine. We know that the R10 makes at least 675 bhp. If we factor that down to the WTCC restrictor area the engine would produce 260 bhp, which sounds inadequate in a world where circa-290 bhp is the going rate for petrol engines. But most believe that the R10 makes at least 700 bhp – factor that down and the figure is 270 bhp. In fact Bagur tells us that the Seat engine makes 280 bhp as opposed to the figure of 280 PS/262 bhp quoted by the official press release.

That same press release quotes maximum torque at 2500 rpm as 450 Nm but that is equally misleading. At 4000 rpm this 280 bhp engine is producing bmep of 31.3 bar and torque of 498 Nm so it follows that the maximum figure at 2500 rpm is at least 499 Nm! The bmep is almost certainly higher than that of the R10: its maximum torque is in the region of 1200 Nm, from bmep of 27.45 bar. This suggests that the WTCC engine might use a higher compression ratio. More likely it exploits a richer air/fuel mixture than the Le Mans engine.

All such turbo-diesel engines run an excess of air over stoichiometric to avoid emission of visible smoke (not permitted by the regulations) and to minimise deposits in the combustion chamber, which build up over time and thus degrade performance. The air/fuel ratio will accordingly be somewhere in the region of 17:1 – 21:1 through the normal operating speed range.

Both the Volkswagen Group Le Mans and WTCC engines use a Dow Automotive particulate filter to help eliminate visible smoke and both exploit organiser-mandated fuel, the former supplied by Shell, the latter by Italian specialist Panta Racing Fuel. Both engines use a Bosch common rail injection system, although the operating pressure of the Seat system is ‘only’ 1600 rather than 2000 bar and unlike the R10 system it does not exploit the precision of piezoelectric injectors. Nevertheless, logically an engine designed to run only 200 kilometres between rebuilds can get away with a richer mixture than one designed to run a 24-hour race.

Like the R10, by gasoline standards the WTCC engine must benefit from an exceptionally strong power curve, substantial engine performance (“more torque than the petrol engine” in racing driverspeak) helping overcome the weight handicap of a turbo-diesel engine. The Seat engine package is officially quoted as being 35 kg heavier than its gasoline counterpart.

The car in any case by regulation has to carry an additional 50 kg or so compared to its gasoline counterpart but the additional engine weight is upfront, compromising weight distribution (the engine is transversely mounted, its crankshaft axis close to the front wheel axis with charge cooler set ahead). The turbo-diesel engine performance and weight must also challenge the front tyres of this front wheel drive machine.

Initial testing revealed the Leon TDI to be slower in the corners than its gasoline WTCC counterpart, reflecting weight and tyre issues, but faster on the straights, by which we can read that it comes off the turns faster: the power curve has indeed more substance. In fact the Leon WTCC contender has always been found wanting for speed on the straights so Seat sees the TDI replacement as a good remedy for that!

Triple Eight Astra

Triple Eight Race Engineering, which is GM brand Vauxhall’s technical partner in UK motorsport developed the Astra RallyD with 1.9 litre turbo-diesel engine for this season. Homologated for Group N rallying, this car has an engine co-developed by Triple Eight in the UK and Sodemo in France. Like a Diesel 2000 competition car it breathes through a 962 mm2 intake air restrictor but there the similarities end. Unlike Diesel 2000 the Group N regulations keep the engine essentially stock. Very little internal modification is permitted and the engine must be equipped with its stock injection and turbosupercharging systems. In the case of the Astra RallyD the size of the stock turbocharger keeps the plenum pressure to a maximum of 1.9 bar absolute, even though the control system can be remapped. The upshot is maximum power in the region of 200 bhp. So far Triple Eight and Sodemo have not been asked to codevelop a Diesel 2000 engine for GM.

BMW DIESEL RACERS

BMW was a pioneer of turbo-diesel power in Touring Cars, winning the 1998 Nurburgring 24 Hour classic outright with a (2.0 litre, 3-Series) 320d. This year privateer Rick Kerry has made a low-key entry into the British Touring Car Championship with a 120d Diesel 2000 car supplied by BMW Motorsport. Currently a 3.5 litre BMW 135dBD is a leading force in Germany’s ‘Long Distance Touring Car Championship’. Ageratec, a Portuguese biodiesel producer is a backer of this car, likewise supplied by BMW Motorsport. Biodiesel is the focus of Scott Racing in the UK, which earlier this year received a grant of £62,000 from national government via regional agency One NorthEast. That grant was specifically for Scott Racing in conjunction with Durham University to develop a biodiesel-fuelled car for the British Touring Car Championship. Currently the project partners are working on a 320d that has the latest E90 turbo-diesel engine. The aim is to have a full Diesel 2000-specification car running in the 2008 BTCC. Scott Racing’s Ian Dixon tells us that this project is independent of BMW Motorsport and is not tied to a specific biodiesel producer. At present potential fuels are being evaluated at Durham University. The aim is not to find the one with the highest cetane number but to find a clean-burning fuel with consistency of supply. For example, Dixon says that fuel from rape seed oil can vary from batch to batch since different seeds provide different characteristics. Dixon is confident that the right biofuel will provide a cleaner burn than regular fossil fuel, which should permit the engine to rev higher.

Added to the database on 3^rd October 2007