I.C. ENGINESEngine Testing

Practical No: 3(24 Mar, 2014)

RigsDiesel Engine

Diesel Engine and Test Bench• Naturally aspirated• 4-stroke• Indirect injection• Water- cooled engine • Bore 190 mm• Stroke 320 mm• Maximum engine speed 450 rpm• Equipped with a centrifugal engine speed regulator

that regulates the injected fuel amount engine speed is kept constant

Rigs SI Engine

SI Engine and Test Bench• Naturally aspirated• 4-stroke• Side valve• Water-cooled• Variable compression ratio,• Single cylinder engine• Exceptionally robust • Bearings and running gear are adequate to withstand severe

knock.• Externally mounted gear pump delivers oil to a splash

lubrication system for the large end bearing, cylinder and cam shaft

SI Engine and Test Bench• Crank shaft main bearings are pressure fed.• Up-draught carburetor fitted with an adjustable main jet to

permit• variation of mixture strength • Ignition is by magneto and the spark timing may be varied • Bore 85.0 mm• Stroke 82.5 mm• Compression ratio can be set (continuously) between 4.0 and

10,0• Maximum engine speed is 2000 rpm, Minimum velocity• depends on engine settings, usually being between 800 and

1000 rpm• Cooling water is supplied by an external electric driven pump

Equipment Used• Hourly fuel consumption Ch is measured by measuring the time

needed to consume a given volume of fuel and knowing the fuel’s density ρf

• Densimeter Fuel Measuring System• The density is measured with a densimeter • Time with a chronometer • The volume of fuel is measured using a graduated pipette There

are two pipettes, with the volumes of 100.0 cm3 and 250.0 cm3.

Equipment Used• Thermocouple• Exhaust temperature is measured by a thermocouple located

at near downstream of the exhaust valve, and the temperature is directly read in an analogue gauge

• De Prony Brake

Equipment Used• De Prony Brake

DrumStripLever

FbWheel

Wooden Break Block

Equipment Used• De Prony Brake• A drum of radius r is attached to the driveshaft. • The drum is embraced by a metal stripe with a series of

wooden brake blocks. • The metal stripe can be tightened by means of a wheel

around the drum, and is attached to a lever of length b, and it has a variable weight F at its extremity.

• The lever can oscillate within certain limits, but when it is steady, the torque of the friction force between the wooden brake blocks and the drum is balanced by the moment of the lever.

• The determination of this moment allows the torque at the drum to be known, and that torque is the engine brake torque Be .

Equipment Used• The entire de Prony Brake has a certain weight,

which, together with the distance of its application point to the axis of the drum, represents a certain torque. If that weight is reported to the application point of the variable weight F, then that virtual weight W should be added to F, and the moment is then given by b (F + W). Therefore

• B = b (F +W)• The values of b and W is constant and = to 1.200 m

and 73.5 N.

Equipment Used• Mechanical Tachometer• Brake power is obtained multiplying the torque Be by

the driveshaft angular speed ω. This speed can be converted to rotations per unit of time.

• The appropriate scale of the tachometer should be chosen, and the rubber end mounted on its axis should be pressed (strongly) against the engine driveshaft.

Equipment Used S.I.Engine• Rotameter Flowmeter • Water flow is regulated by a valve and its flow rate

measured with a rotameter flowmeter • The rotameter has two scales. The scale to use is in

the metal side.

Equipment Used• Analogue Thermometers • The water inlet and outlet temperatures are

measured by analogue thermometers

Equipment Used• Fuel Consumption Gauge • Hourly fuel consumption Ch is measured by

measuring the time needed to consume a given volume of fuel and knowing the fuel’s density ρf

Equipment Used• Chronometer • Time is measured with a dedicated chronometer• Engine speed

Equipment Used• Fuel Consumption Gauge• The volume of fuel is measured using a cylindrical

glass tube fuel consumption gauge with spacers

Equipment Used• Fuel Consumption Gauge• The volume of fuel is measured using a cylindrical

glass tube fuel consumption gauge with spacers. Spacers are machined to a knife edge for part of their circumference and are positioned so that a measured volume of fuel is contained between successive spacers.

• Volume between them is 25.0 cm3

25.0 cm3 and 50.0 cm3

Equipment Used• Engine Speed• Engine speed is calculated • Number of rotations is counted only while the

chronometer is running• The pair (no. of rotations - time) then allows

calculating the average engine speed during the time interval measured.

• The dedicated counter / chronometer has also a Tachometer to allow an easy verification of the engine speed, but it should not be used to provide values for calculations.

Equipment Used• Air consumption meter• The air flow rate is measured by means of an

air consumption meter • This unit consists of a large plenum chamber

upstream of the engine air filter. • The air exits the plenum chamber

intermittently to the engine, but due to the large volume of that chamber, the air is virtually quiescent inside the chamber.

Equipment Used• Air consumption meter• Thus the air enters the chamber at a steady rate,

making it possible to calculate the flow rate by measuring the pressure loss at the chamber’s inlet with a manometer and by knowing the pressure loss coefficient of the inlet.

• The diameter of the inlet to the plenum chamber is 19,9 mm and the inlet pressure loss coefficient is 0.60.

Temperature and Pressure• The air temperature and pressure upstream of

the inlet have to be known. • With these two values, with the diameter D

and the pressure loss coefficient K, and the pressure drop p across the inlet, the air flow rate can be computed:

Equipment Used• Exhaust Temperature Display • Exhaust temperature is measured by a

thermocouple located at near downstream of the exhaust valve, and the temperature is directly read in a digital display

Equipment Used• DC Electrical Generator and Electrical

Resistances• The brake is an electrical DC one with a

nominal output of 3500 W at 220 V and 2000 rpm, and a speed range up to 3600 rpm.

Equipment Used• DC Electrical Generator and Electrical

Resistances• Machine is shunt wound and separately

excited by a DC electrical generator

Equipment Used• DC Electrical Generator and Electrical

Resistances• The electrical output is absorbed in a

separately mounted load unit with ten electrical resistances

Equipment Used• DC Electrical Generator and Electrical

Resistances• The electrical load is controlled by a separate

free standing electrical control cabinet

Equipment Used• Ambient thermometer, barometer, and hygrometer• When testing engines, ambient pressure and

temperature should always be measured, thus allowing corrections to be made. These corrections are meant to present the results in terms of standard atmospheric conditions, and hence to have results

• that are independent of the local conditions. Relative humidity should also be measured, although corrections are not usually made to take it into account.

How to Measure Brake Torque• The brake torque is measured by measuring

the force F necessary to prevent the brake to rotate, keeping it balanced

• The force F is measured with a dynamometer and acts at the end of a lever

• To reach the balance of the brake the wheel that controls the dynamometer needs to be adjusted

How to Measure Brake Torque• Power is obtained from the torque and from the

brake (and therefore engine) speed. • The length of the lever is 265 mm.• Therefore, brake torque and power are:

• with Be in N·m, F in N, Pe in W, and n in rpm.• The electrical brake may enforce resistant torque

to the engine (and allowing to measure it) or motor torque (allowing to start the engine, as well as to measure mechanical losses by the method of engine motoring).