BMW launches six-cylinder diesel engine with four turbochargers on the 7-Series

Article by Christian Andrei, on May 19, 2016

BMW is introducing the world’s most powerful six-cylinder diesel engine yet in the BMW 7 Series luxury sedan. This new diesel engine, a 3.0-liter six-cylinder in-line unit, will be featured in the new BMW 750d xDrive and new BMW 750Ld xDrive models that will be available starting July 2016. Based on BMW Group’s latest generation of engines, this diesel unit is a recipient of that BMW TwinPower Turbo technology that employs multi-stage turbocharging with four turbochargers and the recently updated common-rail direct injection system that could generate over 2,500 bar of maximum pressure. Of course, this new diesel is also loaded with an array of technological updates and innovations that should make it superior to its outgoing counterpart in terms of power delivery, pulling power and efficiency.

The new 3.0-liter six-cylinder in-line engine could deliver 294 kW (400 hp) in maximum output at 4,400 rpm and 760 Newton-meters (560 lb-ft) in peak torque available between 2,000 rpm and 3,000 rpm. Amazingly enough, this diesel engine could cough up over 450 Newton-meters (332 lb-ft) of torque at just 1,000 rpm. With these numbers, the BMW 750d xDrive could accelerate from zero to 100 km/h (62 mph) in 4.6 seconds, or 0.3 seconds better than its predecessor. Meanwhile, the BMW 750Ld xDrive could sprint from nil to 100 km/h in just 4.7 seconds. This remarkable and sharper boost in acceleration is mainly attributed to an evolved version of multi-stage turbocharging that now employs four turbochargers instead of just three.

This setup results to a faster buildup of boost pressure at lower engine speeds, which allow for amazingly rapid responses to throttle operations from idle. Thanks to the engine massive yet and sustained wave of thrust as well as to an eight-speed Steptronic transmission that is capable of sending most of this power to the wheels, both BMW 750d xDrive and BMW 750Ld xDrive are able to achieve immediate and intense bursts of tempo under throttle inputs at higher speeds.

Also, both the BMW 750d xDrive and BMW 750Ld xDrive have an electronically limited top speed of 250 km/h (155 mph). In the past, such amounts of ferocious power and dynamism come at the expense of fuel economy. But that is not in the case of the diesel engine fitted in the new BMW 750d xDrive and BMW 750Ld xDrive. This engine maybe the most powerful diesel unit, but it is simply superb in the areas of fuel efficiency.

Compared to its predecessor, this new six-cylinder in-line engine delivers 14 kW (19 hp) more output and 20 Newton meters (15 lb-ft) more torque; and its average fuel consumption and emissions are lower by 11 percent. In fact, the new BMW 750d xDrive and new BMW 750Ld xDrive consume between 5.9 liters and 5.7 liters per 100 kilometers – or between 47.9 mpg and – 49.6 mpg imp (average, combined), and emit between 154 grams and 149 grams of carbon dioxide per kilometer (as per EU test cycle).

Powertrain

The diesel engine wonder that now powers the new BMW 750d xDrive and new BMW 750Ld xDrive is the latest proof of BMW Group’s mastery of auto engineering as well as its expertise in the field of drive system development. BMW Group has installed in this 3.0-liter six-cylinder in-line diesel engine an array of state-of-the-art features that allowed it to deliver excellently in terms of power generation and efficiency.

This masterful and innovative engine development – as underpinned by the principle of combustion under extremely high pressure – resulted to a unit that could perform better than its peers. An elemental factor in the development of the base engine – part of the BMW Group’s latest generation of drive systems – is the fact that the German premium carmaker was able to lay out the necessary foundations.

Thus, BMW Group was able to tailor detail solutions that addressed both the thermal and mechanical loads that usually tag along with extremely high outputs and the rise in peak combustion pressure from 200 bar to 210 bar. Just like its predecessor, the new diesel engine has its cylinder head and crankcase manufactured in a special high-pressure compression process called Hot isostatic pressing (HIP), which makes sure that the aluminum castings are particularly strong. Moreover, BMW employed a tie rod concept in the assembly of the main bearing caps and cylinder head, as augmented by a central screw.

The new diesel engine also features cylinder bores with a twin-wire arc-sprayed coating and aluminum/silicon alloy pistons with re-melted bowl rims and a five-layer cylinder head gasket, as well as bronze liners in the pin eyes and centrally controlled cooling. Fuel supply to the engine is handled very well by the latest generation of common-rail direct injection technology that employs piezo injectors.

The injectors – featuring a peak injection pressure of over 2,500 bar – ensure precise metering and fine atomization of the fuel, resulting in higher fuel efficiency and lower emissions. Both the new BMW 750d xDrive and the new BMW 750Ld xDrive have an exhaust treatment technology that includes a diesel particulate filter, a NOX storage catalytic converter and an SCR (Selective Catalytic Reduction) system with AdBlue injection. One of the most interesting new features of this six-cylinder diesel engine is the use of the fourth turbocharger – the first time that this extra feature is employed. The use of four turbochargers as well as the precise and coordinated interplay of all components in the turbocharging system has allowed the engine to offer such a high level of performance and effectiveness.

This new engine – just like its predecessor – features the so-called multi-stage turbocharging that is responsible for the generation of a flow of compressed air into the combustion chambers. Two compact turbochargers with variable turbine geometry integrated into a single housing are involved in the high-pressure stage. A third and larger turbocharger is used to handle the low-pressure stage, but it has since been replaced by two smaller and faster responding turbos. BMW employed the latest iteration of Digital Diesel Electronics (DDE) to handle engine management and to implement a deployment strategy that would coordinate: the roles of each turbochargers; the position of the high-pressure system’s variable vanes; and the regulation of the change-over and bypass flaps, the waste gate, the exhaust gas butterfly valve and the intercooler according to operational situations and throttle inputs.

The four turbochargers – two high-pressure and two low pressure units – are always in operation. The only time the two low-pressure turbochargers would be bypassed – through a flap control system – would be under hard acceleration from idle. Bypassing the two low-pressure turbos would allow boost pressure to build up faster. When the engine speed reaches about 2,500 rpm, the second high-pressure turbocharger would be brought into play. On the other hand, the new diesel engine features exhaust gas recirculation for both the low-pressure and high-pressure stages of the turbocharging system – a feature not found in its predecessor.

Exhaust gas recirculation does not only enhance the effectiveness of the turbochargers and of the engine, but also ensures that lower levels of nitrogen oxide emissions under high loads. Moreover, the new engine makes use of a higher capacity indirect system of charge air cooling and an extra compressor backplate cooling for the low-pressure turbochargers. This extra compressor backplate cooling system -- featuring a low-temperature circuit separate and independent from the engine’s cooling system – comes with heat exchangers and an electrically operated coolant pump.

Press Release

Celebrating its premiere in the BMW 7 Series model range: the world’s most powerful six-cylinder diesel engine.

An impressive spread of innovations mark the new BMW 7 Series luxury sedan out from the crowd. The spread of new features runs from a Carbon Core body structure and BMW eDrive technology in the three BMW iPerformance models to BMW gesture control and Remote Control Parking. And now another new arrival has joined the fray. The world’s most powerful six-cylinder diesel engine is making its debut in the BMW 750d xDrive and BMW 750Ld xDrive (fuel consumption combined: 5.9 – 5.7 l/100 km [47.9 – 49.6 mpg imp]; CO2 emissions combined: 154 – 149 g/km), which come as standard with intelligent all-wheel drive. The new unit generates maximum output of 294 kW/400 hp and peak torque of 760 Newton metres (560 lb-ft).

The new 3.0-litre six-cylinder in-line engine was developed on the basis of the BMW Group’s latest generation of power units. Its BMW TwinPower Turbo technology includes multi-stage turbocharging with four turbochargers and common-rail direct injection, the latest update of which generates maximum pressure in excess of 2,500 bar. These and other technological highlights allow significant improvements to the already exceptional power delivery, pulling power and efficiency achieved by the outgoing engine. The new BMW 750d xDrive accelerates from 0 to 100 km/h / 62 mph in 4.6 seconds (BMW 750Ld xDrive: 4.7 seconds) – an improvement of 0.3 seconds over its predecessor. Much credit for this even sharper dynamic edge can go to a new form of multi-stage turbocharging, which now brings together four turbochargers in place of the previous three. This enables boost pressure to be built up even more quickly at lower engine speeds and therefore prompts incredibly swift responses to throttle applications from idle.

Top-level efficiency: engine output up 5 per cent, average fuel consumption down 11 per cent.

The new generation of the world’s most sportingly gifted six-cylinder diesel engine develops its maximum output of 294 kW/400 hp at 4,400 rpm. Its optimised performance characteristics are reflected most prominently in torque development that gathers pace rapidly and from low engine speeds. Indeed, the engine serves up over 450 Newton metres (332 lb-ft) of torque at just 1,000 rpm and puts its maximum 760 Newton metres (560 lb-ft) on tap between 2,000 and 3,000 rpm. The engine’s large and sustained wave of thrust and the eight-speed Steptronic transmission tuned to make the most of it together ensure that instant and ferocious bursts of pace can also be achieved under throttle inputs at higher speeds. The BMW 750d xDrive and BMW 750Ld xDrive have an electronically limited top speed of 250 km/h (155 mph).

Added to which, the most powerful diesel engine ever offered by BMW also stands apart with a balance of brawn and fuel economy unmatched by any rival in this engine segment. A 14 kW/19 hp (i.e. 5 per cent) increase in output and peak torque up by 20 Newton metres (15 lb-ft) are accompanied by a 11 per cent reduction in average fuel consumption and emissions over the predecessor model. The new BMW 750d xDrive and new BMW 750Ld xDrive record combined fuel consumption of between 5.9 and 5.7 litres per 100 kilometres (47.9 – 49.6 mpg imp), while CO2 emissions are 154–149 grams per kilometre (figures based on the EU test cycle, may vary depending on the tyre format specified).

Performing at its best under high pressure: new top-of-the-line diesel features numerous technological highlights – from cylinder head to exhaust treatment.

The new sporting king in the diesel ranks represents a masterful example of the engineering art and further evidence of the BMW Group’s outstanding expertise in drive system development. A host of innovative features in the engine’s construction have enabled the signature benefits of diesel engines in terms of power delivery and efficiency – underpinned by the principle of combustion under extremely high pressure – to be showcased at the highest level. Essential foundations had already been put in place in the development of the base engine, a member of the BMW Group’s latest generation of drive systems. Specific detail solutions address both the thermal and mechanical loads that come with extremely high outputs and the increase in maximum combustion pressure – from the previous engine’s 200 bar to 210 bar.

As with the outgoing unit, the cylinder head and crankcase are manufactured in a special high-pressure compression process. Hot isostatic pressing (HIP) ensure the aluminium castings are particularly strong. The assembly of the main bearing caps and cylinder head is based on a tie rod concept, complete with a central screw to give extra strength. Other special features include the now five-layer cylinder head gasket, cylinder bores with a twin-wire arc-sprayed coating and pistons made from an aluminium/silicon alloy with remelted bowl rims, bronze liners in the pin eyes and centrally controlled cooling.

The latest generation of common-rail direct injection technology takes care of the fuel supply. The piezo injectors, whose maximum injection pressure has been increased to over 2,500 bar, ensure extremely precise metering and fine atomisation of the fuel. As a result, the engine’s efficiency has increased and its emissions have been reduced. The exhaust treatment technology at work in the BMW 750d xDrive and BMW 750Ld xDrive includes not only a diesel particulate filter and NOX storage catalytic converter, which are positioned in a combined housing close to the engine, but also an SCR (Selective Catalytic Reduction) system with AdBlue injection.

Treading new ground: four turbochargers working together as a precisely coordinated team to deliver enhanced driving pleasure.

The effectiveness and performance characteristics of the new engine are determined largely by the first ever use of a fourth turbocharger and, above all, the precisely coordinated interplay of all the components in the turbocharging system. As with the outgoing engine, the performance-boosting flow of compressed air into the combustion chambers is generated by multi-stage turbocharging. The high-pressure stage revolves around two compact turbos with variable turbine geometry integrated into a single housing, while a single, very large low-pressure turbocharger has been replaced by two smaller – and therefore faster-responding – units. The latest-generation Digital Diesel Electronics (DDE) responsible for engine management adopt a precisely defined deployment strategy to coordinate the activity of the individual turbos, the position of the high-pressure system’s variable vanes, and the regulation of the change-over and bypass flaps, the exhaust gas butterfly valve, the wastegate and the intercooler in response to the operating situation and throttle inputs.

Generally speaking, the two low-pressure turbochargers and one of the two high-pressure turbos are permanently in action. Only under hard acceleration from idle will the two low-pressure turbochargers be bypassed by means of a flap control system. This allows boost pressure to be built up even more quickly. The second high-pressure turbocharger is brought into play at an engine speed of about 2,500 rpm.

Another new feature not present in the outgoing engine is exhaust gas recirculation for the low-pressure stage of the turbocharging system as well as the high-pressure stage. This measure increases the effectiveness of the turbochargers and therefore of the engine as a whole. In this way, levels of nitrogen oxide emissions under high loads are also reduced. To enhance efficiency, the engine also employs an indirect system of charge air cooling with higher capacity than that used by the outgoing engine, as well as additional compressor backplate cooling for the low-pressure turbochargers. Key to the latter is a separate low-temperature circuit – independent of the engine’s cooling system – which includes heat exchangers and an electrically operated coolant pump.

The BMW 750d xDrive and BMW 750Ld xDrive will be available from July 2016.

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