I.C. ENGINES Engine Testing Practical No: 3 (24 Mar, 2014)

Rigs Diesel 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 C h is measured by measuring the time needed to consume a given volume of fuel and knowing the fuel’s density ρ f 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 cm 3 and cm 3.

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 Drum Strip Lever F b Wheel 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 B e.

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 m and 73.5 N.

Equipment Used Mechanical Tachometer Brake power is obtained multiplying the torque B e 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 C h is measured by measuring the time needed to consume a given volume of fuel and knowing the fuel’s density ρ f

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 cm cm 3 and 50.0 cm 3

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

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