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Originally Posted by coombsie66
WutPutt: If you could find that info it would be great! Cheers.  |
I messed up a little bit saying I had some detailed info at home about the 535d, cause I haven’t, I confused it with an article I have about the E60 M5 engine. I hope to ease the pain with some highres tech-pics I ordered. I’ll receive them somewhere next week.
But I can give some more info about multi-stage turbocharged engines. You already know how the system works and what the point of it is. So I’ll try to give some more detailed info. Sadly I don’t have loads of info, but nevertheless here it goes:
1.9 Opel OPC diesel
Opel introduced a multi-stage turbocharged diesel engine on their Vectra OPC prototype end 2003. This engine is based on Alfa/Fiat’s 1.9 JTD 16v diesel engine. With the multi-stage turbocharging it produces 212 bhp and 400 Nm of torque (@ 1400 rpm). Since the filling efficiency of the cylinders is augmented with the multi-stage turbocharging concept.
So how is this system controlled? In below pic gives the scheme of the twinturbo concept for the OPC diesel. Both intake and exhaust have their valves. The one in the intake is actuated by a pressure difference and the one in the exhaust is electronically controlled. The exhaust manifold is directly connected to both big (below on the picture) and small turbo (above on the pictures). The pipe going to the small turbo has a high flow resistance like you can see on the above picture of the engine. The pipe going to the big turbo has a far larger section and lays more inline with the exhaust manifold. But a valve controls the flow going through this pipe.
At the intake side the airflow always passes through the big turbocompressor. After the big compressor the flow can go two separate ways: via the small turbocompressor or just directly to the intake manifold (and thus bypassing the small compressor). Notice also both intercoolers: one between the big and small turbocompressor and one before the intake manifold.
Below 1800 rpm the exhaust control valve is closed. The exhaust gasses can only go through the small turboturbine. Since this one has a low inertia it can deliver a high boost very fast. After the small turbine the exhaust gasses flow over the big turbine, but they only have the energy to let is spin. The big turbo doesn’t produce any boost at this stage.
On the intake side the fresh air passes through the big turbocompressor, but like already said he doesn’t deliver boost. This is why the control valve keeps being closed. So the whole inlet flow has to pass through the little turbo.
Between 1800 rpm and 3000 rpm, the big turbo also begins to deliver boost. Both turbo’s work together. The ECU opens the exhaust control valve a little bit (the ECU opens this valve continuously more for higher revs). So a part of the exhaust gasses drive the big turboturbine. The big turbo starts to deliver boost. But the boost still isn’t high enough to open the intake control valve so all the airflow also has to go through the small turbo. This phase is explained in the below scheme.
And finally under full load and above 3000 rpm the ECU opens the exhaust control valve fully. Since the pipe going to the small turboturbine has a high resistance almost no exhaust gasses will follow this path and the small turbo will just spin without delivering boost. On the intake side the big turbocompressor can deliver enough boost to open the intake control valve. The big turbo can blow the air straight through both intercoolers since the air doesn’t need to go through the small turbo. The big turbo can deliver enough flow to ensure loads of power. The below scheme illustrates this phase.
BMW’s 535d
This one is actually gone into production. This 3.0 sixpack diesel produces 272 bhp (@ 4400 rpm) and 560 Nm of torque (@ 2000 rpm). This engine is extremely high revving for a diesel but already gives 500 Nm of torque free at 1500 rpm. These facts give away the main advantage of this engine: it can rev high and have a lot of power (for a diesel) due to the big turbo but it also has loads of torque at low rpm thanks to the little blower.
The main concept of the 535d engine and the way it works is exactly the same as for the OPC diesel. But there are some differences. Firstly the valve controlling the flowratio between the little and big turbo in the inlet is not automatically controlled by the pressure difference like the OPC engine, but is electronically controlled by the engine ECU. Secondly the exhaust pipe between the little turbo and exhaust manifold doesn’t has such a high flow resistance as with the OPC diesel. But it still is higher compared to the exhaust gases going from the exhaust manifold to the big turbo. And finally in contraire to the OPC diesel there’s only one intercooler, positioned after both turbocompressors.
Highres detailed tech pictures will follow later on.
Sequential turbo information
but just theoretically interested in such matters.
Good luck on that one mate.
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