Ch-5-W-10-11- turbocharging.ppt

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  • Turbocharging

  • C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra*Week-10Turbocharging function and principle of operationDesign considerationsTurbocharging arrangementsArrangement of exhaust pipes.Exhaust manifold pressure diagramPressure & Pulse turbocharging; Pulse convertors2-stage turbocharging .

    Week-11Centrifugal CompressorsConstruction and operationCompressor map and characteristicsRadial compressorsWaste-gate arrangementTransient response of a turbocharged engineProblems & Limitations of turbo chargingMatching of turbochargers-PrinciplesTurbocharger matching routineNumerical Design problems

    C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra

  • Work Available from Ideal Exhaust Process. The energy consists of the Blow-down energy after reversible adiabatic expansion from condition 1 (where the exhaust valve opens) to ambient pressure at point 2-area 1-2-3; andThe work done by the piston in displacing remaining exhaust gases, area 3-4-5-6 (in the case of 4-stroke engine).*

  • *Working of TurbochargerA centrifugal compressor pulls air through a rotating wheel at its center, accelerating the air to a high velocity, which flows radially outward through a shell-shaped housing. The air velocity is slowed after leaving the wheel, which converts velocity energy into pressure. This type of compressor is a high speed device running at 80,000 to 130,000 rpm.Since the turbocharger uses a majority of the energy of the exhaust gases, the sound of the exhaust is muted to a great extent and the engine runs more silent. Of the fuel energy available for an engine, about 40% is wasted in the exhaust.A turbocharger uses some of this waste energy to drive a turbine. The turbine in turn runs a compressor which is mounted on a common shaft inside a common housing.

  • *Design Considerations-Operating range and characteristicsPressure of the exhaust gas entering the turbine is only slightly higher than atmospheric, and only a very small pressure drop is possible through the turbine. In addition, this non-steady-state pulsed flow varies widely in kinetic energy and enthalpy due to the velocity and temperature differences that occur during blowdown and the following exhaust stroke. A pseudo-steady-state flow is assumed, with

    Because of the limited pressure drop through the turbine, it is necessary for it to operate at speeds upward of 100,000 RPM to generate enough power to drive the compressor. These high speeds, along with the high-temperature corrosive gases within which the turbine operates, create major mechanical and lubrication design challenges.

    Turbochargers should be mounted as close as possible to the cylinder exhaust ports so that turbine inlet pressure, temperature, and kinetic energy can be as high as possible.

  • *Operating range and characteristics..One problem associated with turbocharging is the slow response time experienced when the throttle is opened quickly. It takes several engine cycles before the increased exhaust flow can accelerate the turbine rotor and give the desired pressure boost to the inlet air-fuel mixture. To minimize this turbo lag, lightweight ceramic rotors with small rotational moments of inertia are used that can be accelerated quicker. Ceramic is also an ideal material because of the high temperatures.Gas entry temperatures are about 1000 K on diesel engines, and up to 1200 K on spark ignition engines.Torque output from the turbine must always balance the demand from the compressor, whether running at constant load or accelerating. In automotive applications, torques generally range up to not much more than about 10 Nm.Most turbochargers currently in use on diesel engines operate at compressor pressure ratios of the order of 2 to 2.5 : 1, though the trend is upwards. On spark ignition engines, lower ratios are generally required because detonation has to be avoided. Ratios as high as about 3.5 :1 are not too difficult to achieve and manufacturers are now looking at ratios of up to 4.5 : 1. The latter require compressor rotors of materials stronger than aluminium alloy.

  • C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra*Turbocharger Assembly - details

    C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra

  • *Arrangement of exhaust pipesIn a 4-stroke engine, the exhaust valves (EV) are normally open for a period of 2400 in the 7200 of one power cycle.The important aspect of scavenging takes place during valve overlap period. This requires that there should be definite pressure difference between the charging air pressure and the exhaust back pressure (when more than one exhaust pipes are joined together for the purpose of supercharging).Therefore, the EV must be closed at or, before a time when the pressure inside the cylinder has equalled the pressure in the exhaust manifolds. If the EV is closed a bit late, the exhaust pulses would reverse their direction and enter the cylinder leading to charge dilution.If two exhausts are joined successively in the firing order, the exhausts would overlap considerably and, therefore, the exhaust pressure would always be greater than the charging pressure.The EV is generally open for a period of 2400 out of 7200; therefore, 7200/2400=3. Hence for the above reason, not more than three exhausts are joined together so as to maintain a minimum spacing of 2400 between successive exhausts.

  • C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra*

    C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra

  • C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra*Example for 8-cylinder.Firing order 1-3-5-7-8-6-4-2Duration of EV opening period=2400;Gap between successive opening of EVs in firing order = 7200/8 = 900.Condition-No overlap between the opening periods of the connected exhaust pipes.Can we join three exhausts together?1 2 3 4 5 6 7 8

    Cyl. No`FromTo1024039033051804207270510836060064506904540602630150

    C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra

  • C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra*Arrangement of exhaust pipesFor Various types of engines

    C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra

  • *Types of Turbocharging Processes

    There are two basic approaches: constant pressure and pulse turbocharging.

    In his early attempts, starting in 1909 with a multi-cylinder four-stroke diesel engine, Bchi applied the constant pressure principle, which, however, is now used only on some large industrial engines.

    Types:-Pressure chargersPulse chargersPulse Converters

    Pulse turbocharging, despite the fact that turbine efficiency is reduced by pulsating flow, is virtually universal for automotive applications.

  • CONSTANT PRESSURE TURBOCHARGINGThe exhaust from all the cylinders are made to discharge into a common large chamber at pressure higher than atmospheric pressure.

    Gases from all the cylinders expand in the exhaust valves to an approximately constant pressure in the common manifold and pass from here to the turbine.*Buchis early constant pressure turbocharging (1925)

    Not efficient enough to maintain a reasonable boost pressure, but many engine do operate today with this system.

  • C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra*Principle of Constant pressure turbocharging - single cylinder.The large volume of the exhaust manifold ensures constant pressure (Pp);During exhaust process, the cylinder pressure (Pcyl) drops to almost equal Pp.With a sufficiently high turbocharger , the inlet manifold pressure (Pm) slightly exceeds the exhaust manifold pressure. Thus, during valve overlap period, some fresh air flows through the cylinder.Cylinder pressure diagramExhaust pressure diagram

    C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra

  • Constant pressure charging..Advantages.Because of constant pressure & temperature, the turbine runs on a specific pressure ratio and hence better efficiency. If the turbine runs at full speed, which is the case when the number of cylinders joined together are a multiple of three, and turbine pressure ratio is 3:1 or, more, this method is more efficient than the pulse method.Simple design with simple exhaust pipes.The exhaust piping is very simple for a multi-cylinder engine, therefore, a single, highly efficient turbine can be used.When the pressure ratio of compressor and turbine are high, the recovery of the blow down energy is very efficient. Better fuel consumption than the pulse charging are obtained.The engine speed is not limited by the pressure waves in the exhaust pipes.

  • Constant pressure charging...

    Disadvantages.The exhaust system becomes bulky due to the requirement to keep pressures constant. This requires large diameter pipe. This effect is more marked in the case of small engines.Response is poor to sudden load changes- only a small increase in energy in the constant pressure pipes is available to meet the increased requirement of acceleration at high loads. Scavenging is poor due to back pressure because of the requirement of higher pressure drop across the turbine for higher efficiencies.At part load, the efficiency of the turbine reduces due to lower pressure and temperature of the gases entering the turbine.

  • PULSE CHARGINGA disadvantage of the constant-pressure charging is that it does not fully utilize the kinetic energy of the gases leaving the exhaust port. This flaw is corrected here.The actual exhaust pressure pulses are made to run the turbine.Gases pulses are led through narrow exhaust pipes by shortest possible route to the turbine; recovering large proportion of energy.As soon as the exhaust valve opens, a pulse of supersonic velocity exhaust gases are forced into the pipes; creating partial vacuum, leading to better scavenging. At the end of the exhaust, the pressure in the exhaust pipes is much below the cylinder pressure, further improving the process of scavenging.Preferably, separate exhaust pipes are used so that exhaust process of various cylinders do not interfere with each other.*Applications:-Best suited for AFVs.Leopard Mk-II (MB872 engine).Merkava (AVDS 1790 C).Challenger (CV12 Roles Royce)

  • *Pulse turbocharging - Principle of Operation..The pressure-time diagram shows that, the exhaust manifold pressure is no longer constant; as compared to the constant-pressure charging.Constant pressure charging

  • *Pulse turbocharging - Principle of Operation...The flow into the turbine is highly unsteady and will be atmospheric for most of the time.When the pressure wave arrives at the turbine entry, the turbine will tend to accelerate and, decelerate when the pressure wave decays (due to power absorption by the compressor).Thus, the pulse system has increased the available energy at the turbine, but has reduced the efficiency of its conversion into compressor work.For this system to work efficiently, the unsteadiness of the flow at the turbine entry must be reduced.

  • *Pulse turbocharging - Principle of Operation....To reduce the flow unsteadiness, narrow exhaust pipes from many cylinders are connected to a common turbine.The pulses from additional cylinders help fill in the voids in the pressure diagram (Pp).

  • Pulse charging...Advantages1. Recovery of exhaust blow down energy is quite high except, in case of highly supercharged engines with one/two cylinders per turbine inlet.Response to sudden loading is better due to rapid acceleration of the turbocharger because of recovery of very large amount of blow down energy in a short time.Smaller space required due to short & small diameter pipes.Better scavenging at part loads due to partial vacuum and reduced pressure in the exhaust pipes.*

  • Pulse charging...DisadvantagesThe recovery of the blow down energy is poor if the pressure ratio of the turbine is high. This is due to higher throttling losses occurring across the valves because of very low pressure in the exhaust pipes between each exhaust cycle.Complicated inlet & exhaust pipe arrangements needed for large number of cylinders.Poor turbine efficiency due to intermittent gas supply.The scavenging process is disturbed if the exhaust pulses tale too long to travel upto the turbine.*

  • PULSE CONVERTER*Pulse turbocharging has been found to be superior to pressure system on the majority of today's diesel engines.Generally it is used on all but highly rated engines designed for constant speed or, loads or, marine applications.Pulse turbocharging is usually most effective when groups of three cylinders are connected to a turbine entry. However, when only one or, two cylinders are connected, the average turbine efficiency and expansion ratio tend to fall due to the wide spacing of the exhaust pulses.The Pulse Convertor has been developed to overcome some of these disadvantages on certain engines as a compromise between the pulse and constant pressure system.

  • PULSE CONVERTER*124635CONSTANT PRESSURE TURBINEVENTURI JUNCTION BOX ( Maintains constant pressureVENTURI JUNCTIONPulse converter Increases speed of Gases for better ScavengingCombines advantages of both; pulse and pressure charging.Turbocharger turbine is a constant pressure machine and requires steady flow Conditions for maximum efficiency (Pulse charging provides partial admission Operation). However at low level of available exhaust energy especially at part load, pulse charging required for efficient utilization of energy and better scavenging.


  • Compound EnginesC-5-W-10-11-Turbocharging - Prof (Col) GC Mishra*When turbine is not running at its optimum speed due to part load therefore, producing less quantity of exhaust gases, the compressor does not give the desired boost of air delivery. In fact then, it acts as a liability.To overcome this problem, the turbine is so coupled to the engine through appropriate gearing, the deficient power to run the turbine is provided from the engine crank shaft; similar in principle, to a conventional mechanical supercharger. This raises the boost pressure and hence the power output at low speed.A free wheeling device may be used to engage or, disengage the drive from the engine to the turbine.Attractive power output and torque characteristics; but, not commercially successful primarily due to its complexity

    C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra

  • *The estimated Performance Curve for the Compound engine.Turbine efficiency, t=0.8; compressor efficiency including transmission losses, c X mech=0.75Gas-Generator Power PlantThe graph shows that at a pressure ratio of 7.6:1, the engine power output alone balances the requirement of the compressor.At this condition it is possible to envisage an alternative engine, mechanically driving a compressor with no net crank shaft power output.The turbine would not be connected to the compressor, but its power o/p will be harnessed directly, replacing the engine as the power source.

  • Gas-Generator Power Plant*The engine and compressor combination alone would form a self-supporting gas generator that is, generate a high energy exhaust gas flow. The turbine converts this to useful power output.This gives rise to the concept of free-piston engine i.e., so called because the device which produces the useful power is piston-less i.e., the turbine.Not commercially viable.

  • 2-Stage Turbocharging(for upto 18-25 bar bmep)*For engines requiring very high boost pressure not attainable by single stage turbocharging.Two turbines or, two compressors on a single shaft or, use two-stage turbocharging.Two turbochargers of different sizes in series High pressure (HP) stage operating on pulse system-To avoid back pressure and have better responseLow Pressure (LP) stages operating on constant pressure system-for better efficiency.

  • 2-Stage Turbocharging(for upto 18-25 bar bmep)C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra*

    C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra

  • 2-Stage Turbocharging

    *AdvantagesVery high boost pressure in a wide operating range at low cost by using two standard turbochargers.Better efficiency due to high boost pressure. Gain can be further improved by employing after-charge cooler.Due to wide operating range, matching is more flexible but, complex.Better transient response.Combines the advantages of both the constant pressure and pulse charging systems.Disadvantages.Space requirement is more.Bulky.Matching is complex and problematic.

  • *CompressorsCentrifugal or, axial compressors preferred over reciprocating compressors:-To handle a relatively large volume of air.Deliver at large boost pressure (4-6 atmosphere).Highest possible efficiency.Better mechanical coupling with the high speed turbine.Centrifugal compressors axial compressors

  • *Axial or radial flow?Axial flow turbines and compressors, although capable of operating at pressure ratios up to about 12 :1, suffer the disadvantage that,As size is reduced, so also is the available annular space for accommodating the blades, and clearances between blade tips and casing become increasingly a greater proportion of the total cross-sectional area of flow. Consequently, manufacture to very close tolerances is necessary. Additionally, boundary layer flow becomes increasingly significant, tending to choke the flow increasingly as passage sizes are reduced. Furthermore, the number of components needed is very large and, because of the extremely high temperatures, costly materials have to be used.

    Turbochargers with radial compressors and turbines are;Much lighter, simpler, more compact and less costly. However, as the size increases, heat transfer from the turbine rotor becomes a problem. More significantly, it is difficult to cast satisfactorily large one-piece rotors of materials affording high strength at elevated temperatures.

  • *Centrifugal CompressorsStationary inlet casing (sometimes provided with an air filter & noise reducing bafflesRotating impellerStationary diffuser of the vane less or vaned (preceded by a vane less gap) type, and The collector or, volute

  • *Centrifugal CompressorsJet engine cross section showing the centrifugal compressor and other partsCut-away of a centrifugal pump

  • For simplicity, suffixes have been omitted in Figs , but normally lines of constant speed parameter N/T01 and efficiency are plotted on a graph with the co-ordinates,

    P02/P01 and mass flow parameter (T01)/P01,

    where,N is the speed of the compressor rotor in rev/min, is the mass flow rate, and P and T respectively are the pressures and temperatures that would exist in the gases if their flows were suddenly brought to rest under isentropic conditions.

    Suffixes 01 and 02 indicate inlet and delivery condition in the compressor and 03 and 04 in the turbine.Typical performance map for a compressor without a vaned diffuser. *

  • *Compressor surge and stallTwo compressor phenomena liable to be confused are surge and stall. SurgeSurge is initiated if the energy imparted to the gas by the compressor falls below that needed to overcome the adverse pressure gradient between inlet and outlet: the flow suddenly collapses, as a result of which the output pressure drops to a level at which it can then be re-established. This process is repeated cyclically.It is marked by a complete break-down of the continuous steady flow through the compressor. When the flow through the compressor is less than certain limiting value, a surge/pulsation begins and the air surges to and from through the compressor instead of giving a steady flow in one direction.As the flow further reduces, there is a tendency on the part of the compressor speed to shoot up and coupled with it, the turbine speed also shoots up leading to mechanical failure in extreme cases. The pressure ratio may also go up which is not desirable.These occurrences can damage the rotor seals, rotor bearings, the compressor driver and cycle operation. Most turbomachines are designed to easily withstand occasional surging. However, if the machine is forced to surge repeatedly for a long period of time, or if it is poorly designed, repeated surges can result in a catastrophic failure.Of particular interest, is that while turbomachines may be very durable, the cycles/ processes that they are used within can be far less robust.

  • *StallStall increases the resistance to flow, and therefore may or may not help to initiate surge. It occurs when the streamline flow through the compressor breaks away from boundary layers over the surfaces of components such as the radial blades, or diffuser walls or vanes. Breakaway occurs when the velocity, and therefore energy, of the streamline flow becomes inadequate either to sweep the boundary layers along with it or to maintain the Bernoulli depression at a level high enough to hold the streamlines down on the surface.The latter condition can arise if the angle of attack between the flow and, for example, a diffuser vane, increases beyond a critical level. Stall may or may not become a cyclic phenomenon: if it does, it is termed rotating stall.

  • *EffectsCompressor axially-symmetric stalls, or compressor surges, are immediately identifiable because They produce one or more extremely loud bangs from the engine. Jets of flame emanating from the engine are common during this type of compressor stall. An increased exhaust gas temperature, An increase in rotor speed due to the large reduction in work done by the stalled compressor and,In the case of multi-engine aircraft -- yawing in the direction of the affected engine due to the loss of thrust. Severe stresses occur within the engine and aircraft particularly from the intense aerodynamic buffeting within the compressor.Sukhoi T-50 PAK FAsuffering a compressor stallResponse and recoveryThe appropriate response to compressor stalls varies according the engine type and situation, but usually consists of immediately and steadily decreasing thrust on the affected engine. While modern engines with advanced control units can avoid many causes of stall, jet aircraft pilots must continue to take this into account when dropping airspeed or increasing throttle.

  • C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra*The Surge-line shown in Figure is the curve that passes through the lowest flow points of each of the speed lines. As a test map, these points would be the lowest flow points possible to record a stable reading within the test facility/rig.

    C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra

  • *ChokingAt constant speeds as the mass flow rate of the air increases, the boost pressure decreases. This is because, if the mass flow rate is very high, the compressor chokes with excess air.The pressure ratio drops to unity at point C when the valve in the delivery line is fully open and all the power is fully absorbed in overcoming the internal frictional resistance.CThe speed lines of gas turbine centrifugal compressors typically exhibit choke. This is a situation where the pressure ratio of a speed line drops rapidly (vertically) with little or no change in flow. In most cases the reason for this is that close to Mach 1 velocities have been reached somewhere within the impeller and/or diffuser generating a rapid increase in losses. Higher pressure ratio turbocharger centrifugal compressors exhibit this same phenomenon.

    Real choke phenomena is a function of compressibility as measured by the local Mach number within an area restriction within the centrifugal pressure stage.

  • *The surge limit is shown clearly on the left, and the limit on the right is that set by choking of the flow. Between the two are the loops of constant Efficiency. The horizontal arcs represent constant-speed conditions. A limitation is the onset of local supersonic gas flows in the compressor.Another is that, as pressure ratio increases, the useful range of operation tends to become progressively narrower

    Operating range and characteristics.Typical performance map for a compressor without a vaned diffuser. (pressure ratio plotted against mass flow parameter); where N is the rotational speed of the rotor and T and P the absolute temperature and pressure)

  • Superimposed on the compressor map in Fig are engine-operating (air requirement) lines at both constant speed and constant load. At constant load the lines rise steeply as engine speed is increased. The air requirement for constant speed, on the other hand, rises much more slowly, because it increases only with the rate of increase of fuelling, instead of with engine speed.Operating range and characteristics.....*

  • CHARGE COOLING*Turbocharging increases the temperature, and therefore reduces the density of the charge. It does so in three ways. By the addition of the energy of compression. Turbulence in the flow through the compressor also adds heat, doing so increasingly as compressor efficiency falls off. Some heat is transferred from the turbine to the compressor.After-cooling helps to compensate for the consequent loss of density.Until recently, air-to-water after-cooling was generally favoured, because of its compactness. Now, however, the situation has changed, an example of an outstandingly good design and a compact installation being the air-to-air charge cooler on the Ford Mondeo 1.8-litre turbo diesel engine shown in Fig

  • CHARGE COOLING..*Cooling the charge after compression brings the following benefits. By virtue of the increase in density of the gas delivered, a higher power output, potentially between about 20 and 25%, is obtainable. Lower temperatures in the cylinders reduce the thermal loading on both the engine and the turbine and, because friction losses are not significantly higher, bmep is increased, and specific fuel consumption is improved by between 3 and 5% (though, because charge cooling is greatest when the mass air flow is low, these benefits are obtained mainly at low engine speeds). With a cooler charge, the output of NOx will be reduced. Also, the engine operating lines at constant speed swing over to run more nearly parallel to the surge line, and the constant load lines move away from the surge line on the compressor map.Consequently, all the operating lines tend to fall in the areas of high efficiency, Fig. on next slide, and matching may be easier.

  • *After-cooled engine running lines (full) superimposed on the running lines without inter-cooling (dotted). It can be seen that the engine can be matched more easily to the compressor, by moving the after-cooled lines to the left, mainly because the maximum load line is more nearly parallel to the surge lineCHARGE COOLING


  • *Limitations of turbocharger and superchargerCost and complexityDetonationSpaceTurbo lag

  • TORQUE/SPEED & RESPONSE LAG ; TURBOCHARGERS1. Turbocharging provides most power increase at high engine speed , resulting into an engine which does not pull well at low speed.

    Furthermore, at light engine load the turbocharger speed drops, and it must rise again before the engine can accept full load; leading to a lag in responding to the sudden demands for increased power.

    If at the design stage smaller nozzles are fitted in the turbine housing, the gas flow is impeded & the pressure drop increased. So more power is taken from the gases, the turbocharger is moved faster, giving more boost at all engine speeds.

    - In the mid-speed range power may now be satisfactory,

    - But at high engine speed, the engine may be over-boosted or,

    the turbocharger over-speeded to destruction.

    4. Waste gate control valve provides a solution.

  • WASTEGATE CONTROL Waste gate control valve is opened automatically as boost pressure rises too high, allowing some of the exhaust to bypass the turbine.

    This is one of the several techniques for modifying the intrinsic power / speed curve of turbocharged engines to make it more suited to automotive use.

  • STRESS PROBLEMS IN PRESSURE CHARGED ENGINESTo achieve compactness, most MBT engines are fiercely boosted, well beyond the usual limits of commercial vehicles. This leads to:-- Mechanical stressing within the engine, blowing it apart;- Thermal stressing, burning/ melting it.

    The design of the engine must ensure,- Better detailed design from cylinder head to cylinder joints,- Better layout of the internal cooling circuits,- Better materials in valves and piston crown,- Oil cooling of the pistons,- Charge cooling.

    3.But, ultimately the last option open is to reduce the compression ratio.

  • *Design ConsiderationsPrinciples of turbocharger matchingContinuity of mass flow.Turbine work = Compressor work.Turbine speed = Compressor speedTCEngine0123

  • *Design Considerations1. Continuity of mass flow.TCEngine0123

  • *2. Compressor work.TCEngine0123

  • 3. Turbine work.TEngine23

  • 4. Temperature after compression.TCEngine0123

  • 5. Heat Supplied. To find T2TCEngine0123

  • 6. Compressor work=Turbine work

  • TURBOCHARGER MATCHING ROUTINEGiven: f, v, i, Vs, N, CV, , , Cpc/Cpt, t, P0, T0, K, RCompressor map ant turbine map

    Guess P1 Therefore, rc=p1/po.

    Guess c (70-75% for turbochargers. Then find,

    Find .

    Find Xc

  • *TURBOCHARGER MATCHING ROUTINE..5.Plot rc and Xc on compressor map; find cIf cc, make a better guess and repeat. Else, proceed.

    6.Find T2

    7.Find and thus rt


    In fact, this is not required. From rt, we find Xt from the turbine map.

    Find p3

    Compare p3 with p0.If p3>p0, increase p1 and repeat.If p3

  • *Exercise-1A turbocharger has the characteristic shown in the figure and is used to turbocharge a 4-stroke diesel engine of swept volume 10.3 litres. At low speed of 1000 rpm, the rack is fully open and fuel injection is 0.95 gram per cycle. Estimate the boost pressure (it is thought to be about 1.7 bar) and the Air-Fuel ratio.The following data is given:-CV = 42000 kJ/kg.Heat loss to radiation and to coolant = 23% of heat supplied.Cpc= 1.05 kJ/kg.KRatio of Cp in compressor to turbine = 0.9Turbine efficiency = 0.7Inlet air = 1 bar, 293 K.K ((-1)/)= 0.286; R = 287 J/kg.KIndicated thermal efficiency of the engine = 0.42Volumetric efficiency = 0.9

  • *Compressor MapWith superimposed with Engine operating lines

  • *Turbine Map

  • *Tutorial-1Figure shows the compressor map and the turbine characteristic (marked A) to be used on a turbocharged 4-stroke diesel engine. The following data is given:-CV = 42000 kJ/kg.Heat loss to radiation and to coolant = 23% of heat supplied.Cpc= 1.05 kJ/kg.KRatio of Cp in turbine to compressor = 0.9Turbine efficiency = 0.7Inlet air = 1 bar, 293 K.K ((-1)/)= 0.286; R = 287 J/kg.KIndicated thermal efficiency of the engine = 0.42Volumetric efficiency = 0.9Swept volume = 10.3 litre = .0103 m3.Fuel injected per cycle = 0.952 g at full rack. =0.714 g at rack =0.476 g at rack =0.238 g at rackCalculate the matching conditions at full, , 1/2 and rack and at speeds 2100, 1500, and at 1000 rpm.

  • C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra*Compressor MapWith superimposed with Engine operating lines

    C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra

  • *Turbine Map

  • *Tutorial-2A 4-stroke 12-cylinder diesel engine with bore = 7.2 cm, stroke = 9.4 cm and operates at 2500 rpm. The Volumetric efficiency = 1.18 and inlet conditions are 1 bar, 293 K. The compressor map and the turbine (curve-B) characteristic are shown in the figure. A waste gate is fitted to limit the boost pressure to 2.4 bar. Indicated thermal efficiency of the engine is 0.44, Heat loss to radiation and to coolant = 22% of fuel energy.CV = 42500 kJ/kg;Turbine efficiency = 0.72Cpa = 1.01 kJ/kg.K; Cpg = 1.21 kJ/kg.K;a=1.4; g=1.3R = 287 J/kg.KExhaust gas pressure (p2) = 2 bar Engine fuel supply rate= 0.6 kg/min

    Show that Pressure of the exhaust gases (p2) is 2 bar.Determine the waste gate flow rate, air-fuel ratio and the brake mean effective pressure. Take friction mean effective pressure=1.8 bar

  • C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra*Compressor Map

    C-5-W-10-11-Turbocharging - Prof (Col) GC Mishra

  • *Turbine Map