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Honeywell Introduces Parallel Sequential Dual-Stage Turbo for Diesels

Honeywell has introduced a parallel sequential dual-stage turbo system for diesel engines. The system makes its debut on the 4-cylinder engines of PSA group’s Peugeot 407 and 607, and the Citroen C5 and C6—the first such application on a four-cylinder diesel.

Unlike a serial sequential turbocharging configuration, where a smaller high-pressure turbo works in advance of a much larger turbo, the new parallel sequential system uses two small turbos working side by side at higher engine speeds of more than 2,700 rpm, but only one at lower rpm.

A specially-designed and patented progressive control valve accelerates the second turbo even when it is idling during the first engine phase. This transient phase, during which the second turbocharger starts spinning but is not yet hooked up to the air intake, ensures a smooth start-up.

Pressurized air from the first turbo is used to avoid any likelihood of oil leakage. The system also includes a position feedback sensor which is controlled by the Engine Control Unit.

This new two-stage turbo system delivers up to 30% more torque over PSA’s 2.2-liter baseline diesel engine and improves third gear acceleration in the 30 kph - 60 kph range by up to 50%.

The 2.2-liter Peugeot HDi diesel engine now delivers full torque of 330 Nm (243 lb-ft) at 1,300 rpm and 370 Nm (273 lb-ft) at 1,500 rpm, unprecedented in an engine of this size at such low rpm.

The development of the new dual-stage turbo system with PSA began in 2003.

Honeywell is also developing serial sequential dual-stage turbo system expected to be introduced around 2007, and is thus able to provide both parallel sequential and serial sequential solutions.



With proper after-treatment, this would make a great Euro 5 van engine if money were no object. But vans rarely go over 2700 rpm, so it's pointless. This engine is just for the 607 prestige crowd, used for boasting over drinks. For the rest of us, let's see PSA wake up and give us two of these cylinders using the single quick spool turbo.

Rafael Seidl

BMW uses unequal dual sequential chargers with fixed geometry on one of its inline six diesels. Honeywell's system appears to be an attempt to achieve a similar combination of minimal turbo lag and high nominal power rating without infringing on the patents covering the BMW system.

It remains to be seen if Citroen PSA will succeed in persuading buyers in the E segment that a fancy dual charger system will indeed make an inline four comparable with a six-cyclinder engine with a single twin-scroll device. In that segment, performance and NVH are usually considered more important than fuel economy.

Single turbochargers with variable turbine geometry have proven adequate for the diesel engines applied in the high-volume segments.

Gasoline engines are trickier because the mass flow is throttled in part load yet the engine-out temperature is very high at nominal power - Porsche uses a VTG charger featuring exotic materials VW opted to combine a turbo with a detachable supercharger for the top end of its C segment vehicles.

Sid Hoffman

Welcome to 1993 - the MKIV Toyota Supra turbo used this system too; two small turbochargers of equal size, but with a flapper valve of sorts in the exhaust manifold to direct all the exhaust to one turbo at low RPM, then progressively bleed open that valve to pre-spool the second turbo as engine speed and load rise, then once it reached the transition point, the valve would swing open 100% driving both small turbos at full speed.


Using multiple turbochargers to get flat torque curve is no-brainer. But look what Mercedes and BMV achieved on their gasoline engines. By employing sophisticated multi-stage tuned induction and variable valve control, they achieved turbo-like flat torque curve on
NA engines. Notably BMW applied this technology to small engine found in new Mini:
economical 1.6 liter develops 120 hp at 6000 RPM and 160 Nm at 4250 RPM, but amazing 140 Nm at as low as 2000 RPM! Power number is not that impressive (record for NA engines, if I remember right, belongs to Nissan 190 hp 1.6 liter), but again, it is economically-tuned engine. Turbocharged version gets 175 hp.
Looks like low-pressure turbo is dead.


These engines can be used on Minivans like the Citroen C8 and Peugeot 807 - so they will be of use in the non executive sector as well. Also, they will sell this engine on to other manufacturers, so it will see a lot of use.
It would be interesting to see how far down the engine size curve they can go wit this technology. They already have a very good 1.6 HDi engine.
Interesting if they could hyridies the diesels.
A question: how much of a capacitor do you need to store the energy from braking a 1.5 ton car fom 50kph to 0 ?


KE = 1/2*M*V^2

Mass = 1500 Kg

50 Km/h = 50,000 m/3600 sec = 13.88 m/s

KE = (1/2)*(1500)*(13.88^2)

KE= 144675 Joules

energy stored in a cap = 1/2*C*V^2

Pick a V and solve for C.

I'll pick 288 volts.

So solve for C

C = 2*KE/V^2

C = 2* 144675 / (288^2)

C= 3.48 Farads

So say you have 50 F caps with a max voltage of 2.5 such as the powerstor


You would need 1150 (or so) 115 in series and 10 strings in parallel to get that capacitance.

or about $15K worth of parts.

1 BTU = 1055 joules (approx)

1 gallon of diesel = ~ 139,000 BTU

So each time you discharge the cap bank you are offsetting that much fuel that you don't have to burn.

In our case .00098781 gallons of diesel (approx)

How much diesel will $15k buy you at $3 per gallon?

5000 gallons or 731650 x10^6 joules

How many charge discharge cycles of our pack is that?

731650x10^6 / 144675 = 5,057,197 cycles

(the pack ends up having a higher capacity so using those numbers it works out to closer to 4 million cycles)

A super cap bank has an expected life of 100's of thousands to 1,000,000 cycles where a NiMh battery might only be good for 1000 cycles.

Rafael Seidl

Andrey -

whenever you see a perfectly flat torque curve in a given RPM range, it's due to artificial limits in the engine control logic. This protects the engine and the rest of the drivetrain against excessive torque. Chip tuners often raise those limits at the risk of shortening drivetrain life expectancy.

Mahonj -

ignoring rolling and wind resistance during the decelaration, the equation boils down to

0.5*m*v0^2 = 0.5*c*(umax^2-umin^2)/eta

where m (your 1500kg) is the mass of vehicle, already adjusted for rotating components and including 150 kg of payload. For reference, this implies a vehicle curb weight of ~1300kg. v0 (your 50kph) is the initial velocity prior to deceleration. C is the equivalent series capacitance of the capacitor pack and umax its maximum permissible equivalent series voltage. Note that the reciprocal of c is the sum of the reciprocals of the capacitance of each cell while umax is the sum of the maximum permissible voltage across one cell (commercially available ultracap designs can handle up to 2.7 volts).

Umin is the minimum voltage at the pack's terminals, dictated by the maximum permissible current imax (~300 amps) and the minimum desired brake power at the wheels Pmin = umin*imax/eta. The power level associated with an instantaneous deceleration a is equal to m*a*v, where v is the instantaneous vehicle speed, i.e. Pmin = m*a0*v0. Since the terminal voltage across the capacitor pack rises as the vehicle slows down, the theoretically feasible deceleration for a given capacitor pack is much higher at low speeds. There are practical limits due to comfort requirements, though. Figure amax < ~0.25g. To minimize the number of expensive an bulky capacitors you have to employ, figure umin = umax/4.

Eta is the aggregate efficiency of the transmission path, including drivetrain, electric generator, power electronics and the capacitor bank itself. Ultrapcacitor cells can be charged with very high efficiency (and hence, low heat dissipation) if and only if enough time is available. A normal, non-emergency deceleration at 1/4 g from 50kph takes about 5.5 seconds. As explained above, any practical design will deliver less than maximum recuperative deceleration at even higher speeds. Ergo, you may well have to accept either a really long brake distance (implying a laid-back and prescient driving style) or, rely on the mechanical brakes to assist above e.g. 25 kph. Either way, you can get away with using L-type ultracaps featuring time contants of ~10 seconds. This cuts down on bulk. Figure eta < 0.7 for purely recuperative braking but significantly less if the mechanical brakes are feathered as well.

Assuming a pack containing 100 ultracap cells in series, you'd get umax=270 volts and umin=62.5 volts. Sticking with eta = 0.7, this yields c = ~6 Farad as the capacitance for the pack and ~600 Farads for each cell. Suitable cells are on the market today, e.g.:


The 100 cells come in at around 20kg, figure ~30 for the pack including packaging and control/safety circuitry. Figure ~30 liters for the pack volume. Note that the cells are actually rated for peak currents as high as 3500 amps. Energy capacity is ~66Wh, the kinetic energy of 1500kg vehicle at 50kph, multiplied by eta, is just ~28Wh. This suggests a pack containing just 50 cells would suffice, halving the component cost, weight and bulk.

Pmin works out to ~29kW at the wheels, i.e. ~21kW at the pack terminals. The electric motor should be able to deliver 30kW in overloaded generator mode for 10 seconds without any impact on life expectancy. The four-quadrant power converter must support the range umin...umax at the terminals connected to the capacitor bank and the current imax at u=umin.

Of course, this is just a blue-sky back-of-the-envelope calculation. In a real-world design, the numbers will be a little less rosy.


Ri and Rafael,
Thank you both. What I am trying to get at is how much (cost, weight, volume) would it take to build a system for stop start city driving where you could recover as much energy as possible from normal braking (not emergency stopping).
Am I right to assume that it is not possible to charge a battery that quickly and that battery based regen braking is not very effecient.
Also, another question: if you limit top speed to say 160 kph can you use narrower, lower rolling resistance tyres for even further effeciency while maintaining braking and safety ?
- JM


Note that Maxwell sells some large ultracaps for about $10/Wh in volume. A 40 Wh pack could cost as little as $400 vs. the $15,000 quoted by rj above.


Yes, but you are talking about wastegate arrangement on turbocharged engines. NA engines does not have it, and use all air engine could ingest at any RPM. The only thing tuners could do whatever concerns logic is to overrich mixture and push spark advance to “best torque” setting, in exchange of massive increase of CO emission and wasted fuel – on full throttle only. It delivers increase of torque and power for about 5%, which is not as little as it sounds. I did such tricks. If you want more, you have to make mechanical alterations or move to nitro-blended fuel or nitro injection.

Practically all modern NA engines use tuned intake, which due to pressure-wave arrangement of intake runners delivers up to 120% of volumetric efficiency, but only at fixed and narrow RPM band. This band could be arranged to deliver max power at high RPM, or higher torque at middle rpm for better driveability. Variable geometry intake runners, so successfully demonstrated by Mercedes and BMV, vastly widens RPM band of increased volumetric efficiency, increasing both max power and mid-RPM torque without complications of turbo/super charging.



Look at :


Maxwell and Alcoa are developing ultracap/battery starting system for cars. Valuable technical information could be found at Maxwell website in PDF format.

John Schreiber

Your NA engines burn gasoline. Diesels must have excess air available to reduce soot emissions and turbo/supercharging is the best solution.

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