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The latest in direct injection engines.

Compiled by Julian Edgar

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Last week we presented an overview of Bosch gasoline direct injection - this time we take a look at some of the engines using the system. These are amongst the most sophisticated internal combustion engines on Earth.

BMW 6-litre V12

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Fitted to the new 760i and 760Li models, the 6-litre BMW V12 develops 327kW/445hp at 6,000 rpm, with maximum torque of 600 Nm/442 lb-ft at 3,950 rpm. A consistent torque level of above 500 Nm/368 lb-ft is maintained throughout the broad speed range from 1,500-6,000 rpm. The BMW V12 complies with the EU4 emission standard in Europe and the LEV (Low Emission Vehicle) standard in the USA, the strictest and most demanding emission standards in the world. Fuel consumption in the EU test cycle is 13.4 litres/100 km or 21.1 mpg Imp. The BMW 760i accelerates from 0-100 km in 5.5 seconds and continues on to 200 km/h in 17 seconds.

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The 12-cylinder is the first direct injection engine from BMW. One high-pressure jet per cylinder injects an exactly dosed amount of fuel directly into the combustion chamber instead of the intake manifold. The engine runs on a homogenous fuel/air mixture (l = 1, or air/fuel ratio of 14.7:1), the initially liquid fuel evaporating during the compression stroke and extracting heat from the ambient air warming up in the compression process. This effect is called "inner cooling" and allowed the engineers to choose the high compression ratio of 11.3:1. This ensured a higher standard of thermal efficiency in the engine, with a corresponding increase in power and torque. Six body sound sensors serve additionally to monitor the combustion curve in each cylinder, ensuring exact management of the combustion process without any knocking.

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The injection jets are positioned in the combustion chambers beneath the intake ducts. The combustion chambers are fully machined on the surface in order to reduce volume tolerance to a minimum, allowing the BMW V12 to run in all world markets without requiring any specific national modifications. The six injection jets - each in the two rows of cylinders - are supplied with fuel by a common rail maintaining fuel injection pressure between 30 and 100 Bar, varying as a function of engine load and speed. The higher the pressure at which fuel is injected, the finer the droplets become and the better the combustion process is. The pressure required for injection is generated by one injection pump on each row of cylinders. These pumps are fitted above the outlet camshafts and are driven by an additional cam between cylinders 4 and 5.

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In addition to direct fuel injection, the V12 also runs the BMW Valvetronic system. Valvetronic uses fully variable intake valve opening times, controlling both the duration and degree of valve motion. This is achieved by the use of an interim lever fitted between the camshaft and the two intake valves on each cylinder. The position of this interim lever relative to the camshaft can be adjusted infinitely by an additional eccentric shaft operated by an electric motor. Depending on the position of the eccentric shaft, the lever converts valve lift into a larger or smaller movement of the valves.

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This puts an end to the throttle butterfly - Valvetronic takes over the function of the throttle butterfly by its infinitely variable intake valve opening period. The advantage in particular is a reduction of fuel consumption when running under part load. As a rule of thumb, the amount of fuel Valvetronic technology saves in comparison with a conventional throttle butterfly increases with the mileage covered under low loads and at low engine speeds. But this technology also helps to save fuel on country roads and the motorway as long as the driver does not use all the power of the engine. (When using full engine power, Valvetronic no longer offers an advantage in fuel economy.) In the European fuel consumption test cycle, Valvetronic reduces fuel consumption by ten per cent compared with conventional throttle butterfly control.

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On a conventional combustion engine, the throttle butterfly is comparable to a hand we put in front of our nose or mouth when we are breathing. Valvetronic, on the other hand, provides either long valve lift (analogous to a deep and long process of inhalation) or short valve lift (a flat and short process of inhalation). BMW sees Valvetronic as the biggest single factor contributing to the achievement of the demanding EU fuel consumption targets in future, requiring a reduction of average fleet consumption to 140 grams CO2 per kilometre by the year 2008.

Valvetronic is based on BMW's infinite camshaft control, which has been in the market since 1992. Called Vanos, this system is an integral part of the Valvetronic concept and plays an important role in achieving smooth output and torque, keeps the engine idling smoothly and masterminds the internal reflow of exhaust emissions in order to save fuel. The BMW V12 power unit features no less than four Vanos adjusters, one for each of the four camshafts.

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Apart from the primary objective to save fuel, Valvetronic offers two other important features:

  • The valves are lifted to their maximum stroke of 9.8 mm only under full load, opening only 0.2 mm when idling and just 1-2 mm at the typical speeds on country roads, meaning a significant improvement of engine smoothness.
  • A further advantage is the unusually good response of the engine whenever the driver presses on the accelerator pedal. This is because the application of load control lies directly next to the combustion chamber. This eliminates the usual time lag between applying throttle and the car actually accelerating, which previously resulted from the need to fill the intake manifold between the throttle butterfly and the combustion chamber.

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The V12 engine block is made of aluminium, while the crankcase - with its open-deck construction for the coolant cavities - is made of an aluminium/silicon alloy and does without cylinder liners; it is therefore very compact. The crankshaft runs in seven bearings. The bottom opening in the cracked forged steel connecting rods is sliced at an angle of 30 degrees, allowing extremely compact design of the crankcase. Despite the roof-shaped piston crown with an integrated trough, the lightweight aluminium pistons weigh just 500 grams each, including the piston pins and rings. This reduces the moving masses to a minimum.

The oil pump operates in two stages to supply a sufficient amount of oil to the four Vanos camshaft adjusters at low speeds and to reliably lubricate the engine, even when idling at only 550 rpm. The aluminium oil sump is double-walled at the bottom in order to further reduce the transmission of sound. With the oil sump being split horizontally into two sections, the upper half serves to effectively stiffen the crankcase and therefore acts as a load-bearing engine component.

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The cylinder heads of the V12 power unit are brand-new from the ground up. For reasons of weight, these are not interchangeable units, but rather different designs fitting exclusively either on the left- or the right-hand row of cylinders.

The complete engine weighs 280kg.

BMW 6-litre V12 Specifications
Maximum output: 327 kW/454 bhp at 6,000 rpm
Maximum torque: 600 Nm/442 lb-ft at 3, 950 rpm
Capacity: 5,972 cc
No. of cylinders: 12
Configuration: 60 degree V12
Stroke/bore: 80 mm/89 mm
Compression ratio: 11.3:1
Spacing between cylinders: 98 mm
Topland width: 9 mm
Conrod centre length: 140 mm
Valve control: Fully variable by BMW Valvetronic; maximum valve stroke 9.8 mm, maintenance-free
Camshaft control: Fully variable intake and outlet; adjustment range 63 degrees CS intake side, maintenance-free
Camshaft drive: By chain, maintenance-free
Valve play compensation: Hydraulic, maintenance-free
Engine management: Bosch MED 9.2.1; one control unit per row of cylinders
Ignition: Solid-state distributor with individual coils and one spark plug per cylinder
Fuel injection: Direct fuel injection with Lambda = 1; system pressure in fuel rail 30-100 bar
Fuel grade: 91-98 octanes, anti-knock control with six sensors
Cooling system: Crossflow cooling with map-controlled thermostat
Intake manifold: Constant intake manifold length; magnesium
Cylinder head cover: Magnesium
Engine weight to BMW standard: 280 kg
Service: Engine oil and filter change, coolant change according to Service Interval Indicator, otherwise maintenance-free
Emission management: Two catalysts next to engine in l = 1 technology with metal substrate; exhaust system made completely of stainless steel</P>
Emission class: EU4/LEV
Fuel consumption (BMW 760i in the EU cycle): 13.4 ltr/100 km (21.1 mpg Imp)

Audi LeMans Car

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Audi used direct injection for the first time on a mainstream race car with their 2001 and 2002 Le Mans winning cars. The system - called FSI - allowed the 3.6-litre V8s to develop over 600hp, despite having to breathe through two 32.4mm restrictors and having the boost of the twin turbos limited to just under 10 psi. Critical in the adoption of the new direct injection technology was a resulting gain in fuel economy under high loads - on the Le Mans circuit full-throttle is used for over 70 per cent of the time.

The existing Audi V8 was modified for direct injection, allowing 'before' and 'after' comparisons to be made. Its design originally comprised a 3.6-litre 90-degree V8, with double-overhead camshafts, a compression ratio of 11.2:1, alloy block with Nikasil coated cylinders, and a flat crankshaft with steel conrods. Maximum performance of this engine was 448kW at 6300 rpm with a peak torque of 700Nm at 5500 rpm. With 90 litres of 98 RON pump fuel, the car could complete 12 laps of the Le Mans circuit (each lap being 13.6km) - a consumption of about 55 litres/100 km! This engine used traditional port fuel injection.

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Early in the design process it was decided that homogenous mixtures (ie not stratified) and air-guided injection should be used for the new engine. The requirements to be met by the engine modifications included:

  • Best positioning of the injector
  • Controlled air motion with a reasonable compromise of efficiency and tumble using a sophisticated inlet port layout
  • Spray geometry which ensured good fuel distribution and avoids wall wetting
  • Good cooling of the relevant components
  • Supply of high pressure fuel to the injectors

To meet these objectives, the heads were redesigned with the central axis of the ports lifted by 2mm, water jackets altered, and the inducement of a 'forward tumble' (as opposed to swirl) pattern of air entry into the cylinder. The injectors were mounted to avoid any contact between the spray and parts like the valve heads and the spark plug tip. In addition, the wetting of the cylinder walls was avoided. Injectors with a flow greater than 40cc per second were needed for the application - larger than any previously existing direct injection designs.

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The higher electrical power demands of the injectors required that external amplifiers be added to the original Bosch MS 2.9 ECU. The fuel was provided by a triple-cylinder piston pump positioned at the rear end of the cylinder head and driven by the inlet cam. It provided fuel at pressures of up to 150 Bar, although actual running pressures were varied electronically between 30 - 100 Bar.

Endurance tests of 36 hours of uninterrupted running were completed on the prototype engine, with the engine constantly cycled in a simulation of a qualifying lap! Following the successful completion of this and other tests, the engine was put into sporting action.

Direct fuel injection resulted in the following benefits on this engine:

  • The compression ratio could be lifted by more than 1 point. (The better efficiency that occurred from this compression ratio change also resulted in a drop in exhaust gas temperature of 50 degrees C. It then became necessary to insulate the exhaust system and turbo in order that enough energy could be provided to the turbo.)
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  • An overall fuel consumption reduction of 8 - 10 per cent was achieved, resulting in the ability to complete another lap. In addition the engine could be driven without misfiring with an air/fuel ratio as lean as 17.6:1.
  • Because of the presence of the restrictors, peak power was little changed. However, the reduced sensitivity to knocking and the raised compression ratio allowed a torque increase by 9 per cent over a wide range.
  • The immediate availability of fuel reduced the starting time of the engine by nearly 1.3 seconds, and the engine was also harder to stall.
  • The direct injection engine had better driveability.

Dr Wolfgang Ullrich, Head of Audi Sport says of the FSI racing unit: "Reduced fuel consumption, more power, better driveability."

Infineon Audi R8 Specifications
Name: Infineon Audi R8
Vehicle type: Le Mans Prototype (LM-P)
Monocoque: Carbon fibre, crash structure ACO and FIA approved, CFC rollbars front and rear, carbon fibre body
Engine: V8, turbo charged, 90 degree cylinder angle, 4 valves per cylinder, 2 Garrett turbochargers, to comply with the rules 2 x 32.4 mm air restrictors and boost pressure restriction to 1.67 bars absolute, direct fuel injection (FSI)
Engine management: Bosch MS 2.9
Engine lubrication: Dry sump, Shell Racing Oil SR
Displacement: 3600 cc
Output: 610 bhp
Torque: 700 Nm
Power transmission: Rear wheel drive
Clutch: CFC clutch
Gearbox: Sequential 6-speed sports gearbox, partner Ricardo
Differential: Multiple-disc limited-slip differential
Driveshafts: Constant-velocity plunging tripod joint
Steering: Servo-assisted rack-and-pinion steering
Suspension: Independent suspension at front and rear. Double-wishbone suspension. Pushrod system with horizontal spring/damper unit, adjustable gas-filled shock absorbers
Brakes: Hydraulic dual-circuit brake system, monobloc light-alloy brake callipers, ventilated carbon fibre brake discs at front and rear, brake balance adjustable by driver
Rims: O.Z. forged magnesium rims, Front: 13,5 x 18 inches, Rear: 14,5 x 18 inches
Tyres: Michelin Radial, Front: 33/65-18, Rear: 36/71-18
Length: 4650 mm
Width: 2000 mm
Height: 1080 mm
Minimum weight: 900 kg
Tank capacity: 90 litres
Alfa Romeo JTS 2-litre
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Available in the 156, the Alfa Romeo JTS ("Jet Thrust Stoichiometric") engine uses Bosch direct injection. This gives the performance of a 2.3-litre unit, yet consumes 10% less fuel. The new 2-litre engine has the same capacity as the Twin Spark engine it replaces, yet power is up from 114kW to 121kW; torque rises from 187Nm to 206Nm. The new engine meets the ultra tough Euro 4 emission standards and despite the performance gains, fuel consumption stays virtually the same - and there is no requirement for low sulphur fuel.

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At low engine speeds, which the engine operates for the majority of the time, it operates as a lean burn engine, while at higher engine speeds it progressively switches to a normal air/fuel mixture. With regard to emissions, the combination of the direct injection and the use of lean burn only at lower engine speeds means that NOx emissions are similar to normal engines. Large NOx catalyst converters are not needed.

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