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THERMODYNAMICS

I.C. ENGINE TESTING

I.C. ENGINE TESTING INTRODUCTION: The basic task in the design and development of engines is to reduce the cost and improve the efficiency and power output. In order to achieve the above task, the ‘development engineer’ has to compare the engine developed with other

I.C. ENGINE TESTING INTRODUCTION: ‐ range of speed. Some engines are made to run at fixed speed by means of speed governor, which is its rated speed. The performance of the engine depends on the inter

relationship between the power developed, speed and the specific fuel

I.C. ENGINE TESTING INTRODUCTION: ‐ consumption at each operating condition within the useful range of speed and load.

I.C. ENGINE TESTING (iii) Brake specific fuel consumption at each operating condition within the useful range of operation. (iv) Reliability and durability of the engine for the given range of operation.

I.C. ENGINE TESTING Purpose of Testing an

I.C.

Engine: In general the purpose or significance of testing an

I.C.

engine is to determine the following: (i) To determine rated power output with respect to the fuel consumption in Kg per Kw

hr of brake power output.

I.C. ENGINE TESTING Purpose of Testing an

I.C.

Engine: (iv) To determine the quantity of lubricating oil required per bp Kw hr. (v) To determine the quantity of cooling water required per bp Kw hr. (vi) To determine the overload carrying capacity of the engine. (vii) To prepare the heat balance sheet of the engine.

I.C. ENGINE TESTING Some Important Terms as per

ISI

Standard:

1. Speed

The speed of an engine is the mean speed of its crank shaft in revolutions per minute

(RPM),

except in case of ‘free piston’ engines where the speed is the number of cycles per minute

of the reciprocating components.

2. Steady Load Speed Band: It is the maximum total variation in speed expressed as a %age of the mean speed, which may occur while there is no change in external load conditions.

I.C. ENGINE TESTING Some Important Terms as per

ISI

**Standard:

Brake Power:** It is the total power measured at the driving shaft. 7. Fuel Consumption: The quality of fuel consumed by the engine per unit time of the stated power and under stated operating conditions. 8. Specific Fuel Consumption: It is the quantity of fuel consumed per unit of power per unit of time. It is generally expressed in gms of fuel consumed per kW hr or B.H.P./bp.

I.C. ENGINE TESTING Some Important Terms as per

ISI

**Standard:

Standard Operating Conditions**

The following are the standard operating conditions: (i) Mean Barometric Pressure: It is taken as

mm of mercury (Hg). (ii) Intake Air Temperature

It is taken as

0 k or 27 0

C

I.C. ENGINE TESTING Indicated Mean Effective Pressure

(P

im

It may be defined as, the constant pressure acting over the full length of the stroke and capable of producing the same amount of work, as is actually produced during the complete cycle of the engine. It is generally denoted by

‘P

im

or i.m.e.p. As, the pressure in the cylinder varies throughout the cycles and the variation can be expressed with respect to the volume or crank angle rotation to obtain p

V

or p ‐θ diagrams,

I.C. ENGINE TESTING Indicated Mean Effective Pressure

(P

im

respectively. However, such a continuous variation does not readily lend itself to simple mathematical analysis in the computation of ip. If an average pressure for one cycle can be used, then the computations become far less difficult. Refering figure, as the piston moves back and forth between

TDC

and

BDC,

the process lines on the p

V

diagram indicated the successive states of the working fluid through the cycle.

I.C. ENGINE TESTING Indicated Mean Effective Pressure

(P

im

p

V

diagram for an ideal four

stroke cycle engine

I.C. ENGINE TESTING Indicated Mean Effective Pressure

(P

im

produced with the varying pressures. P im

X(V

1

V

2

Net work of cycle P im

ே௘௧ ௪௢௥௞ ௢௙ ௖௬௖௟௘ ሺ௏ ଵି ௏ ଶ ሻ Also, P im

஺௥௘௔ ௢௙ ௜௡ௗ௜௖௔௧௢௥ ௗ௜௔௚௥௔௠ ௑ ௌ௣௥௜௡௚ ௡௨௠௕௘௥ ௟௘௡௚௧௛ ௢௙ ௧௛௘ ௜௡ௗ௜௖௔௧௢௥ ௗ௜௔௚௥௔௠ = ௔ ௑ ௦ ௟ If, a= area of indicator diagram in cm 2

l= length of the indicator diagram in cm