turbo charger

TREND OF ‘VGT’ TURBOS IN I.C. ENGINE

 (A Revolutionary energy saver)

ABSTRACT:

This paper mainly deals with effective use of energy.

Now a days we are running sort fossil fuel, so the energy obtained from fossile fuel should be used effectively. In this paper we introduce the variable geometry turbine to capture the gas from exhaust with compressed air from compressor. With the VGT we can change the blade angle which increases mass flow rate of air in to the engine. The maximum efficiency can be obtained from the turbine keeping the vane angle at 70 degree. The engine efficiency

can be increased by this VGT arrangement.

Intro:

Turbochargers:

Turbochargers are forced induction system. It consists of an air compressor and a turbine which are interconnected. The waste exhaust gas leaving to the atmosphere is directed to the turbine which starts to rotate in a high speed (1500 rpm) along with the compressor; the compressor unit sucks the atmospheric air and sends it to the engine along with fuel which in turn gives high power for each explosion that occurs in the cylinder.

This allows more air and fuel in order to get more power. The boost power 0.45-0.55 bar. We are getting more than 50% air into the engine; therefore power is 50% more than normal practice.

Need for the topic:

The time interval between pressing the accelerator pedal and the rotation of turbine is called turbo lag. In order to reduce this we are going for VGT turbochargers.

What is VGT turbocharger?
It is an innovative variable nozzle turbine. It has variable guide vane which has high variable boost pressure as a result we will get high torque even at low engine speed. The variable guide vane regulates gas flow to turbine so as to maintain optimum efficiency.

Variable design vane methodology:

The VGT fixed at the waste gate is having a capacity of changing the swing blade angle or by moving nozzle side walls. This increases the mass flow and which in increases the amount of air entering the engine along with the fuel. This can be done by varying the vane angle.

The above shown is a typical turbocharger having turbine at its left end and an air compressor at the other end. The increase in the efficiency can be easily represented using the mass flow rate and power output calculations

Calculation of mass flow rate:

Mass flow rate of exhaust gas(Mg)

Mass of air(Ma)= Vs  v N

= 1 x  x (0.1078) x0.12065 x 6 x 0.75 x (0.75) x (2400/70)

= 0.1982 kg/s

Mass flow rate of exhaust gas (Mg)= Ma + Mg

 = 0.1982+0.01101

 Mg= 0.209kg/s

Velocity triangle for radial turbine:

 

1. Inlet triangle 2) Outlet triangle

For radial turbine:

β2=0 , hence C2=CO2

α3=0, hence CO3=0

C2 = Ca3

Co3=C3

Simplified velocity triangle:

 

α = Flow angle entering to the rotor,

 = Outlet blade angle,

Power output W = Mg x Cp (U2 Co2 – U3 CO3)

=Mg Cp (U2)²

C2 = Exhaust gas velocity entering to the rotor,

Vr2 = Radial velocity,

U2 = Rotor tip speed,

U3 = Blade speed.

Power output – (When nozzle angle is at 60 degree)

Mg =0.209 kg/s

Mg =  x b x2 x lth x C2 x Z

0.209 = 0.457 x2 x 102 x 0.7 x 102 x C2 x 24

C2 = 136.1 m/s

From inlet velocity triangle:

Sin  = U2/C2

U2 = sin60 x 136.1

U2 = 117.1 m/s

U2 = 3.14 x 0.06 x N/60

N = 37,520 rpm

Vr2 = C3 = cos x C2

= cos 60 x 136.1

C3 = 68.05 m/s

P = Mg (u2)

= 0.209 x (117.87)²

P = 2.9 Kw

Power output- (when nozzle angle is 70 degree)

Mg =0.209 kg/s

Mg =  x b x2 x lth x C2 x Z

0.209 = 0.457 x2 x 102 x 0.6 x 102 x C2 x 24

C2 = 158.79 m/s

From inlet velocity triangle:

Sin  = U2/C2

U2 = sin70 x 158.79

U2 = 149.21 m/s

U2 = 3.14 x 0.06 x N/60

N = 47,496 rpm

Vr2 = C3 = cos x C2

= cos 70 x 158.79

C3 = 54.31 m/s

P = Mg (u2)

= 0.209 x (149.21)²

P = 4.65 Kw

Computational fluid dynamics:

It is an software, where the analyzing of steam involving fluid flow, heat transfer and associated phenomena such as chemical reactions by means of computer based simulations can be done.

Inlet and outlet boundary conditions when nozzle is at 60 degree:

Inlet mass flow rate of exhaust gas(kg/s)	Outlet exhaust pressure of turbine (bar)
0.209	2.169
0.3	2.03
0.4	1.84
0.5	1.697
0.55	1.47

Inlet and outlet boundary conditions when nozzle is at 70 degree:

Inlet mass flow rate of exhaust gas(kg/s)	Outlet exhaust pressure of turbine (bar)
0.209	2.09
0.3	1.87
0.4	1.57
0.5	1.256
0.55	1.47

Variation of flow velocity, turbine speed, power output according to the mass flow rate, when the angle is at 60 degree:

Mass flow rate of exhaust gas (kg/s)	Flow velocity (m/s)	Turbine speed (rpm)	Power output (Kw)
0.209	136.1	37520	2.9
0.3	195.37	53185	8.58
0.4	260.49	71810	20.35
0.5	325.62	89762	39.76
0.55	350.18	98739	52.92

Variation of flow velocity, turbine speed, power output according to the mass flow rate, when the angle is at 70 degree:

Mass flow rate of exhaust gas (kg/s)	Flow velocity (m/s)	Turbine speed (rpm)	Power output (Kw)
0.209	158.79	47498	4.65
0.3	227.9	98169	13.75
0.4	303.9	90903	32.62
0.5	379.87	113631	63.71
0.55	417.8	124993	84.8

Specifications:

Engine:

Bore = 10.718 cm,

Stroke = 12.065 cm,

Capacity = 6538 cc, 6 cylinders,

Max bhp = 125 Kw @ 2400rpm,

Air fuel ratio = 18:1.

Turbocharger:

Type = Holset turbocharger,

Turbine type = Inward radial flow turbine,

Rotor inlet and outlet diameter = 6 cm & 1.9 cm resp.

Hub diameter = 2.5 cm,

No. of blades = 12,

Flow angle at the exit of rotor = 0 degree

Flow angle at the inlet of rotor = 60 degree

Engines exhaust gas property at 800 k:

Density of the gas: 0.457

Dynamic viscosity of gas: 34.84e-6 W/mK

Specific heat at constant pressure of gas: 1185 J/kgK

Conclusion:

Thus from the information’s above we can clearly prove that the engine power output can be increased from 2.9kW to 4.65kW by changing the nozzle angle 70 degree , this prevents the turbo lag so that we preserve power during the starting of acceleration. This clearly shows that there will be increase in power output on adopting VGT. Hence in this era of finding an alternate source of fuel, VGT will be an promising concept so that the fuel used and engine efficiency can be used in much more efficient manner.