DIFFERENCE IN SI & CI ENGINEDIFFERENCE IN SI & CI ENGINE-A REVIEW--A REVIEW-

SN SI ENGINE CI ENGINE

1 DO NOT REQUIRE HIGH CR (8:1 TO 12:1) REQUIRES HIGH CR 13: 1 TO 22: 1.LARGER ENGINES OPERATES AT LOWER CR & SMALLER ENGINES OPERATES AT HIGHER CR DUE TO UNFABOURABLE CYLINDER VOLUME TO SURFACE RATIO AS THE SIZE REDUCES. ( HEAT LOSSES!!!)

2 USES HOMOGENEOUS NEAR STOICHIOMETRIC MIXTURE OF AIR & VAPOURISED FUEL ( NARROW RANGE (11: 1 TO 18:1). PEAK PRESSURE IS LESS AS COMPARE TO CI ENGINE.

DO NOT USE HOMOGENEOUS MIXTURE.FUEL IS INJECTED INTO THE DENSE HOT AIR FROM INJECTORS OPERATING AT HIGH PRESSURE (100 BAR -700 BAR). OVERALL MIXRURE STRENGTH IS 70 -80 % OF STOICHIOMETRIC. PEAK PRESSURE IS HIGH.

3 CARBURETTERS AND FUEL INJECTION. SI ENGINES INJECTS THE FUEL INTO THE INLET MANIFOLD DOWNSREAM OF THE THROTTLE & UPSTREAM OF INLET PORTS.

FUEL IS INJECTED AT HIGH PRESSURE (100 TO 700 BAR) INTO THE CYLINDER FIILED WITH HOT AIR CHARGE( 700 – 800 C) TO COUNTER HIGH PRESSURE AND TO PRODUCE TINY FUEL DROPLETS.

4 SI ENGINES HAVE ROTATIONAL SPEEDS OF AROUND 6000 RPMs.

INHERENTLY LOW SPEED ENGINES. COMMERCIAL TRUCKS HAVE TYPICAL LOW SPEEDS 2000 TO 3000 RPM. FAST RUNNING ENGINES ARE LESS EFFICIENT.

5 SMALLER BAND NEAR STOICHIOMETRIC RATIO IS USED.NO EXCESS AIR AVAILABLE TO COOL .HENCE MAXIMUM CYCLE TEMPERATURES ARE HIGHER

WEAK MIXTURES USED IN DIESEL ENGINES REDUCES THE MAXIMUM CYCLE TEMPERATURES.

6 SHAPE IS CLOSE TO DUAL CYCLE. MODERN CI ENGINES OPERATES BETWEEN OTTO & DIESEL CYCLE(DUAL CYCLE)

DIFFERENCE IN SI & CI ENGINEDIFFERENCE IN SI & CI ENGINE--A REVIEW-A REVIEW-

SN SI ENGINE CI ENGINE

7 LOWER CR GIVES LOWER CYCLE EFFICIENCY.

HIGH CR RESULTS IN BETTER CYCLE EFFICIENCY.

8 LOW CR MAKES THE ENGINE LIGHTER HIGH CR LEADS TO GREATER INTERNAL PRESSURES & MECHANICAL LOADING. CI ENGINES ARE 1.25 TO 2.5 TIMES HEAVIER THAN A TYPICAL SI ENGINES.

9 OVERALL EFFICIENCY ( THERMAL X MECHANICAL) TENDS TO PEAK AND THEN DROPS OFF.

OVERALL EFFICIENCY ( THERMAL X MECHANICAL) TENDS TO PEAK AND THEN DROPS OFF.

10 SI ENGINE OPERATES AT NEAR STICHIOMETRIC RATIO. (14.5 :1)

AIR UTILISATION IS 80-85 % & ( POOR AIR UTILISATION) . AS THE RUNNING CONDITIONS ARE CHANGED THE MIXTURE IS RICHENED & AIR UTILISATION INCREASES . WORK OUTPUT PER CYCLE INCREASES. EVEN AT FULL LOAD WORK OUTPUT PER CYCLE FOR A GIVEN SWEPT VOLUME IS LESS THAN THE SI ENGINE.

11 BMEP 10-11 BAR. BMEP 7-8 BAR. LESS WORK PER CYCLE & HEAVIER ENGINES RESULTS IN INFERIOR POWER TO WEIGHT RATIO.ALSO, TORQUE PRODUCED IS LESS DUE TO LESS WORK PER CYCLE.

12 FUEL ECONOMY IS POOR WHICH GETS WORSE AT PART LOAD DUE TO THROTTLING. PUMPING LOSSES INCREASES.

BETTER FUEL ECONOMY FAVOURS CI ENGINE OVER SI ENGINE. BSFC IS 2/3 OF SI ENGINE.

WHAT HAPPENS IN ANWHAT HAPPENS IN ANInternal Combustion Engine ?Internal Combustion Engine ?

WHCH IS BETTER?WHCH IS BETTER?

PV DIAGRAM-OTTO CYCLEPV DIAGRAM-OTTO CYCLEHEAT & WORK TRANSFERHEAT & WORK TRANSFER

PV DIAGRAMPV DIAGRAMDIESEL CYCLE- DIESEL CYCLE- NOTE THE CONSTANT NOTE THE CONSTANT

PRESSURE HEAT INPUTPRESSURE HEAT INPUT

COMPARING CYCLE COMPARING CYCLE EFFICIENCIESEFFICIENCIES

INDICATED DIAGRAMINDICATED DIAGRAM

PROBLEMS WITH SI ENGINEPROBLEMS WITH SI ENGINEPART THROTTLE- NEGATIVE LOOP BECOMES PART THROTTLE- NEGATIVE LOOP BECOMES

LARGERLARGER

UPRATINGUPRATINGWHAT IS UPRATING?WHY UPRATING MORE

FAVOURABLE IN CI ENGINES THAN SI ENGINES?

HOW TO OBTAIN MORE POWER FROM CI ENGINE?

SUPERCHARGINGTURBOCHARGING

UPRATING OF ENGINESUPRATING OF ENGINES

CI ENGINES HAVE ITS BIGGEST DRAWBACK –EXCESSIVE BULK & WEIGHT.

IN MILITARY APPLICATIONS THAT’S THE BIGGEST DRAWBACK.

IN COMMERCIAL APPLICATIONS THOUGH THESE FACTORS ARE NOT THAT IMPORTANT BUT EUROPEAN LAWS RESTRICT MINIMUM POWER TO WEIGHT RATIOS.

THERE IS AN INTEREST TO EXTARCT MORE POWER FROM ENGINES WITHOUT INCREASING BULK.

ANOTHER REASON IS THE COMMERCIAL PRACTICE WHERE A MANUFACTURER TRIES TO COVER A WIDE RANGE OF POWER WITH LEAST POSSIBLE NUMBER OF BASIC ENGINES. SAY ONE ENGINE FOR 150-200 Kw.

The procedures for extracting more power from a given basic engine is called UPRATING

OBTAINING MORE POWEROBTAINING MORE POWER!! MORE POWER FROM AN EXISTING CI ENGINE CAN BE OBTAINED : A. INCREASING THE ENGINE EFFICIENCY??? B. INCREASING THE FUEL THROUGHPUT???

EFFICIENCY OF A TYPICAL CI ENGINES ARE REACHING A PLATEAU. TYPICAL 40 % . ( IN SOME CASES EVEN 50 % HAS BEEN CLAIMED).

THERMAL EFFICIENCY CAN BE INCREASED BY INCREASING CR.

TO INCREASE THE FUEL THROUGHPUT , AIR THROUGHPUT SHOULD ALSO BE INCREASED.

POSSIBLE METHODS OF INCREASING THE AIR THROUGHPUT: A. CYLINDER SIZE??? ------- AFFECTS COMPACTNESS B. INCREASE VOLUMETRIC EFFICENCY BY BETTER DESIGN ??? CHEAPNESS, QUIETNESS AND RELIABILITY C. INCREASING AIR DENSITY??? POSSIBLE !!!

Why used forced Why used forced induction?induction?By increasing the amount of

oxygen going into an engine, more fuel may be burned

More fuel equals more powerAn engine with F.I. can produce

more power than the same engine without F.I.

This improves the power-to-weight ratio

INCREASING AIR INCREASING AIR THROUGHPUT THROUGHPUT !!

HOW TO INCREASE DENSITY? A. LOWERING TEMPERATURE REFRIGERATION?? POSSIBLE> BETTER COP OF REFRIGERATOR. CAN USE

ABSORPTION TYPE. ADDITION OF BULKY AUXILIARY

B. INCREASING PRESSURE

PRESSURE CHARGING FROM CRANKSHAFT. SUPERCHARGING PRESSURE CHARGING FROM EXHAUST POWER.

TURBOCHARGING

SI ENGINE VERSUS CI ENGINESSI ENGINE VERSUS CI ENGINES

SUPERCHARGING OF ENGINES NOT ONLY INCREASES THE VOLUMETRIC EFFICIENCY BUT ALSO INCREASES THE INTAKE TEMPERATURE.

IN CASE OF SI ENGINES, INCREASE IN PRESSURE & TEMPERATURE REDUCES IGNITION DELAY & INCREASE FLAME SPEED AND HENCE INCREASED TENDENCY TO DETONATE OR PRE-IGNITE.

THIS INCREASED TENDENCY TO DENONATE MAKES IT NECESSARY TO USE RCH MIXTURES RESULTING IN POOR FUEL ECONOMY.

THEREFORE, IN SI ENGINES SUPERCHARGING IS NOT VERY POPULAR.

RECOMMENDED ONLY FOR RACING OR FOR ALTITUDE COMPENSATION.

IN CI ENGINES SUPERCHARGING IMPROVES COMBUSTION –BETTER , QUIETER AND SMOOTHER COMBUSTION.

DEGREE OF SUPERCHARGING IS LIMITED BY THE THERMAL AND MECHANICAL LOADING ON THE ENGINES.

Introduction Introduction

Types of Boosting SystemsTypes of Boosting SystemsMechanical –

Supercharger

P

Exhaust Gas - Turbocharger

Main problem with supercharging is the parasitic loss of having to drive the compressor from the engine output shaft. This loss can be up to 15% of engine output.

SUPERCHARGINGSUPERCHARGINGCOOLANT OUT

COOLANT IN

POWER

EXHAUST

ENGINE

CRANKSHAFT

CHARGE COOLER

SUPER CHARGER

SCHEMATIC DIAGRAM

SUPERCHARGINGSUPERCHARGING POWER MAY COME FROM CRANKSHAFT. COMPRESSOR USED INEVITABLY INCREASES AIR

TEMPERATURE. RISE IN TEMPERATURE REDUCES CHARGE DENSITY. RISE IN AIR TEMPERATURE ALSO INCREASES AIR

TEMPERATURE AT ALL POINTS ROUND THE CYCLE. LEADING TO THERMAL STRESSES. ALSO, MECHANICAL STRESSES ---- INCREASE CHARGE

MASS IN A GIVEN VOLUME IMPLIES GREATER PRESSURE.

COOLING THE CHARGE AFTER THE COMPRESSOR IS WORTHWHILE.

CALLED AFTERCOOLER OR INTERCOOLER ---AIR TO AIR COOLER OR AIR TO LIIQUID COOLER.

NEGATIVE LOOP BECOMES NEGATIVE LOOP BECOMES POSITIVE LOOP !POSITIVE LOOP !

ENERGY BALANCEENERGY BALANCE

TurbochargersTurbochargers

Thermodynamic AnalysisThermodynamic Analysis~30-40% of the fuel

energy is released as exhaust gas energy

Area bounded by points 415 is the theoretical energy available. This is sometimes referred to as blowdown losses

Ideal cycle pressure-volume diagram for a naturally aspirated engine (Baines, 2005)

What are turbochargers?What are turbochargers?Also known as turbos, they are a

device to compress air flowing into an engine.

They are a device for forced induction

TURBOCHARGING -COMPONENTSTURBOCHARGING -COMPONENTS

TURBOCHARGER-CUT TURBOCHARGER-CUT SECTIONSECTION

TURBOCHARGINGTURBOCHARGINGTECHNIQUES OF TURBOCHARGINGCOMPONENTS –TURBOCHARGINGADVANTAGES OF TURBOCHARGINGDESIGN ASPECTS –

TURBOCHARGINGEFFECTS OF TURBOCHARGINGCALCULATIONS -TURBOCHARGING

TurbochargersTurbochargers

The vast majority of turbochargers consist of a centrifugal compressor and centripetal turbine mounted on a common shaft

Compressor

Turbine

Turbocharger compressors are generally centrifugal compressors consisting of three essential components: compressor wheel, diffuser, and housing. With the rotational speed of the wheel, air is drawn in axially, accelerated to high velocity and then expelled in a radial direction.

The diffuser slows down the high-velocity air, largely without losses, so that both pressure and temperature rise. The diffuser is formed by the compressor backplate and a part of the volute housing, which in its turn collects the air and slows it down further before it reaches the compressor exit.

CompressorCompressorDesign and functionDesign and function

TurbochargersTurbochargers

CompressorCompressor

Consists of three elements◦ Compressor wheel◦ Diffuser◦ Housing

Compressor limits◦ Surge line◦ Choke line◦ Maximum Blade

Speed

Operating characteristics of Operating characteristics of CompressorCompressor

The compressor operating behavior is generally defined by maps showing the relationship between pressure ratio and volume or mass flow rate. The useable section of the map relating to centrifugal compressors is limited by the surge and choke lines and the maximum permissible compressor speed.The map width is limited on the left by the surge line. This is basically "stalling" of the air flow at the compressor inlet. With too small a volume flow and too high a pressure ratio, the flow can no longer adhere to the suction side of the blades, with the result that the discharge process is interrupted. The air flow through the compressor is reversed until a stable pressure ratio with positive volume flow rate is reached, the pressure builds up again and the cycle repeats. This flow instability continues at a fixed frequency and the resultant noise is known as "surging".

Compressor MapsCompressor MapsEfficiencies typically range

between 0.5 and 0.8.Maps include lines of constant

compressor speed.Surge line defines regions (to

left) where turbo operation is unstable – surge is common.

Choke lineThe maximum centrifugal compressor volume flow rate is normally limited by the cross-section at the compressor inlet. When the flow at the wheel inlet reaches sonic velocity, no further flow rate increase is possible. The choke line can be recognised by the steeply descending speed lines at the right on the compressor map.

Increasing Horsepower Increasing Horsepower

The supercharger increases horsepower by increasing the weight/density of the mixture and by increasing compression pressures

The supercharger also consumes some horsepower in order to boost total horsepower output

• The exhaust flow from the engine is directed over the blades of the turbine to provide the force to turn the shaft and compressor

• Leaks in the exhaust system before the turbine will decrease performance

• Combustion deposits may form on the turbine and reduce efficiency

• Turbine speed is controlled to change the amount of boost available

Turbine

The turbocharger turbine, which consists of a turbine wheel and a turbine housing, converts the engine exhaust gas into mechanical energy to drive the compressor. The gas, which is restricted by the turbine's flow cross-sectional area, results in a pressure and temperature drop between the inlet and outlet.

This pressure drop is converted by the turbine into kinetic energy to drive the turbine wheel.

There are two main turbine types: axial and radial flow. In the axial-flow type, flow through the wheel is only in the axial direction. In radial-flow turbines, gas inflow is centripetal, i.e. in a radial direction from the outside in, and gas outflow in an axial direction.

Up to a wheel diameter of about 160 mm, only radial-flow turbines are used. This corresponds to an engine power of approximately 1000 kW per turbocharger. From 300 mm onwards, only axial-flow turbines are used. Between these two values, both variants are possible.

Turbine -Design and Function

CENTRIPETAL(RADIAL) TURBINE CENTRIPETAL(RADIAL) TURBINE COUPLED WITH CENTRIFUGAL COUPLED WITH CENTRIFUGAL

COMPRESSORCOMPRESSOR

TurbochargersTurbochargersIntercoolerIntercooler

Temperatures after the compressor can reach 180 C. Cooling the air can offer a significant performance increase.

Simultaneous improvement in output, fuel economy, and emissions Turbocharger

Intercooler

Waste Gate and Exhaust Bypass Waste Gate and Exhaust Bypass Valve Valve

As the waste gate closes, more exhaust is routed to the turbine

As the waste gate opens, more exhaust exits the tailpipe

The more exhaust that is routed to the turbine, the faster it spins, and the more boost that is available

Oil pressure controls the position of the waste gate by pushing on a piston and opposing spring pressure inside the exhaust bypass valve

Each controller senses critical parameters and adjusts oil pressure accordingly.

aeeat NDm 03.0

Air-Delivery Ratio Air-Delivery Ratio

Theoretical air consumption (4-cycle) can be written as,

where a is the density of the air entering the compressor.

Air-Delivery Ratio Air-Delivery Ratio

The deliver ratio, ev, is,

where ma is the air consumption of the engine.

at

av m

me

Air Delivery RatioAir Delivery Ratio

The Ideal Gas Law can also be utilized to estimate ev,

where the subscript 1 denotes the conditions of air entering the compressor, and 2, air exiting the compressor.

2

1

1

2

T

T

p

pev

Compressor Performance MapCompressor Performance Map

Turbine Pressure RatioTurbine Pressure Ratio

The turbine pressure ratio, pt, is defined as,

where the subscripts 3 and 4 denote exhaust gases entering and leaving the turbine, respectively.

4

3

p

ppt

Fig. 8.7: Turbine Performance Maps Fig. 8.7: Turbine Performance Maps

Turbine vs. Compressor Flow RatesTurbine vs. Compressor Flow Rates

The turbine/compressor mass flow rate ration can be written as,

where the mass flow rate out of the engine (mt) is equal to the mass flow rates of fuel (mf) and air (mc) into the engine.

AF

m

m

c

t 1

Selecting a Turbocharger for an Selecting a Turbocharger for an EngineEngine

The pressure ratio across the compressor must first be defined as,

where the “boost” pressure is the pressure rise across the compressor.

12

1 1p

p

p

p boostpc

Selecting a Turbocharger for an Selecting a Turbocharger for an EngineEngine

The corresponding temperature ratio across the compressor can be estimated as,

where ec is the compressor efficiency.

c

pc

eT

T 11

286.0

1

2

Steps for Sizing a TurboSteps for Sizing a Turbo

1) Select an achievable desired power output for the engine in question (pbme<1250 kPa).

2) Calculate the required fuel mass flow rate using a realistic BSFC value (0.20<BSFC<0.25 kg/kWh).

3) Determine the mass air flow rate (25<A/F<32 for CI engines).

Steps for Sizing a TurboSteps for Sizing a Turbo

4) Select a compressor, and the point on the compressor map where the engine will operate at rated speed and power. Previous relationships can be utilized as an aid to finding this point,

This equation must be solved iteratively by assuming a value for ec, and then solving for pc.

aee

a

pcc

cpc

ND

m

e

e

03.01286.0

Steps for Sizing a TurboSteps for Sizing a Turbo

5) Next, the compressor map is entered at values of ma and pc, and ec is determined. If the ec from the solved equation does not match the ec on the compressor map, then the latter ec is used to solve for a new pc, and the process is repeated.

6) Select a turbine and the operating point on the turbine map.

• Remember, the compressor and turbine must operate at the same speed.

• The turbine flow must match the compressor flow times (1+F/A).

• Turbine must supply enough power to drive the compressor and to overcome bearing friction.

Turbocharger Mechanical Turbocharger Mechanical EfficiencyEfficiency

The turbocharger mechanical efficiency (em) can be estimated as,

where Cpc is the specific heat of ambient air at constant pressure while Cpt is the specific heat of heated air at constant pressure.

)(

)(

43

12

TTCm

TTCm

P

Pe

ptc

pcc

t

cm

Turbocharger Mechanical Turbocharger Mechanical EfficiencyEfficiency

The previous equation can be reformulated as,

1

31T

TeeeA

Fmtcavailable

urt

pc

pt

pcrequired pC

C

1

1286.0

k

ku

1

Comment on ProcessComment on ProcessTurbine efficiencies are typically 0.98.Values for Cpc, Cpt and k’ must be

obtained from a table where, the latter two are temperature dependent and should be selected in accordance with the exhaust temperature (T3).

available must be greater than required or the turbine will not drive the compressor fast enough to develop the desired boost.

T3-T2 (temperature rise) across the engine is largely a function of F/A ratio – typically between 480 and 580 C.

Fig. 8.8: Characteristic Fig. 8.8: Characteristic Values of Values of

DesiredOperating

Range

ExampleExampleA turbocharger is to be fitted to a

10 L diesel engine, which is to run at 2400 rpm rate speed and provide a brake power of 180 kW. The density of ambient air is 1.16 kg/m3, the desired A/F ratio of the turbocharged engine is 30:1, and it is estimated the engine can achieve a BSFC of 0.25 kg/kWh.

SolutionSolution

SolutioSolutionn

SolutionSolution

Table 8.1: Engine FamilyTable 8.1: Engine Family

OperationOperationTurbocharger lag occurs when fuel delivery

is rapidly increased. There is a brief period of time when the turbocharger fails to extract enough energy to supply enough air (to match the proper A/F ratio) – resulting in transient black smoke (unburned fuel).

Variable geometry Variable geometry turbochargersturbochargers

• Turbochargers are well matched to piston engine requirements only over a narrow range of rpm.

• New types of turbochargers includes those with pivoting inlet guide vanes, simpler variable inlet

• These turbochargers can extend the range of useful boost, and reduce the low-speed drivability deficiencies of normal turbos. The increased boost can also be translated

Variable geometry Variable geometry turbochargersturbochargers• The main draw back of turbocharged diesel engine is the poor throttle

response in achieving the required acceleration causing irritation to the driver who has to keep in pace with the prevailing traffic flow.

• This is because of the phenomenon called the `turbo lag' or the time lag for the turbocharger to provide the needed pressure boost to the intake air when the driver steps on the accelerator pedal in search of more power. At this time, the turbine is spinning at lower speed and takes a while to spool up so as to supply the needed air for better acceleration.

• The variable geometry turbocharger helps to address this problem. These turbines have movable vanes with adjustable entry angles that respond to turbine speed to provide a more matching level of pressure boost even to a slow spinning turbine without producing too much of a boost at higher speeds.

• Variable-geometry turbocharger is becoming quite popular in European diesel passenger cars, but not yet in petrol driven cars, because the high exhaust temperature characteristics of petrol car makes the design of movable turbine blades a difficult proposition.

• The maximum temperature of the exhaust of a diesel is about 800{+0} C, while the minimum temperature of the gasoline exhaust is about 950{+0} C. Also the wider operating speed range of the petrol car requires the variable geometry vanes to be incorporated in the compressor stage instead of the turbine stage.

VARIABLE GEOMETRY VARIABLE GEOMETRY TURBINETURBINE

TwinCharger SystemTwinCharger System Mechanical superchargers are good for low end output but short

of efficiency at high rev, while exhaust turbochargers works strongly at high rev but reluctantly at low rev.

At low rev, the supercharger provides most of the boost pressure. The pressure it built up also speeds up the turbocharger so that the latter can run into operating range more quickly.

At 1500 rpm, both chargers contribute about the same boost pressure, with a total of 2.5 bar. (If the turbocharger work alone, it can only provide 1.3 bar at the same rev.)

Then the turbocharger – which is optimized for high-rev power – started taking the lead. The higher the rev, the less efficient the Root-type supercharger becomes (due to its extra friction). Therefore a by-pass valve depressurize the supercharger gradually.

By 3500 rpm, the turbocharger can contribute all the boost pressure, thus the supercharger can be disconnected by an electromagnetic clutch to prevent from eating energy.

A grey cast iron bearing housing provides locations for a fully-floating bearing system for the shaft, turbine and compressor which can rotate at speeds up to 170,000 rev/min. Shell moulding is used to provide positional accuracy of critical features of the housing such as the shaft bearing and seal locations.

The turbine wheel is made from a high nickel superalloy investment casting. This method produces accurate turbine blade sections and forms. Larger units are cast individually. For smaller sizes the foundry will cast multiple wheels using a tree configuration.

Journal bearings are manufactured from specially developed bronze or brass bearing alloys. The manufacturing process is designed to create geometric tolerances and surface finishes to suit very high speed operation.

Compressor impellers are produced using a variant of the aluminium investment casting process. A rubber former is made to replicate the impeller around which a casting mould is created. The rubber former can then be extracted from the mould into which the metal is poured. Accurate blade sections and profiles are important in achieving compressor performance. Back face profile machining optimises impeller stress conditions. Boring to tight tolerance and burnishing assist balancing and fatigue resistance. The impeller is located on the shaft assembly using a threaded nut.

The turbine is rarely subjected to constant exhaust pressure. In pulse turbocharged commercial diesel engines, twin-entry turbines allow exhaust gas pulsations to be optimised, because a higher turbine pressure ratio is reached in a shorter time. Thus, through the increasing pressure ratio, the efficiency rises, improving the all-important time interval when a high, more efficient mass flow is passing through the turbine. As a result of this improved exhaust gas energy utilisation, the engine's boost pressure characteristics and, hence, torque behaviour is improved, particularly at low engine speeds.

To prevent the various cylinders from interfering with each other during the charge exchange cycles, three cylinders are connected into one exhaust gas manifold. Twin-entry turbines then allow the exhaust gas flow to be fed separately through the turbine.