Internal Combustion Engine Testing Kanit Wattanavichien

What is I.C. Engine Internal combustion engines (ICE) the internal combustion engine is characterised by: “The working fluid composition changes during its passage through the engine. Energy is released by combustion and the added heat is, in part, converted into work.” strictly speaking, this description includes not only reciprocating engines, but gas turbines as well. In this chapter we will consider only: ‘reciprocating internal combustion engines’ or R.I.C.E

Basic operation of a four stroke engine: Compression Stroke Power Exhaust A I R Combustion Products Intake Air Fuel Injector

Direct Injection quiescent chamber Direct Injection multi-hole nozzle swirl in chamber Direct Injection single-hole nozzle swirl in chamber Indirect injection swirl pre-chamber

Engine Geometry Vd = Compression ratio rc = Vc – Vd Vc

Engine Indicating Diagram & Valve Timing Digram Valve overlaps

Engine P-V Diagram

Cl Engine Indicating & P-v Diagram

Engine Testing Part A Part B Part C Engine Inspection Energy Balance on an Engine and Engine Performance Part C Cylinder Pressure Measurement

Torque is measured off the output shaft using a dynamometer. Torque and Power Torque is measured off the output shaft using a dynamometer. b Force F Stator Rotor N Load cell The torque exerted by the engine is T:

Torque is measured off the output shaft using a dynamometer. Torque and Power Torque is measured off the output shaft using a dynamometer. Load cell Force F Stator Rotor b N The torque exerted by the engine is T: The power delivered by the engine turning at a speed N and absorbed by the dynamometer is: Note: w is the shaft angular velocity in units rad/s

Typical Torque and Power Curve

Torque is a measure of an engine’s ability to do work and power is the rate at which work is done The term brake power, , is used to specify that the power is measured at the output shaft, this is the usable power delivered by the engine to the load. The brake power is less than the power generated by the gas in the cylinders due to mechanical friction and parasitic loads (oil pump, air conditioner compressor, etc… The power produced in the cylinder is termed the indicated power, .

Indicated Work per Cycle Given the cylinder pressure data over the operating cycle of the engine one can calculate the work done by the gas on the piston. This data is typically given as P vs V The indicated work per cycle is given by WA > 0 WB < 0 Compression W<0 Power W>0 Exhaust W<0 Intake W>0

Gross indicated work per cycle – net work delivered to the piston over the compression and expansion strokes only: Wi,g =area A + area C (>0) Pump work – net work delivered to the gas over the intake and exhaust strokes: Wp =area B + area C (<0) Net indicated work per cycle – work delivered over all strokes: Wi,n = Wi,g – Wp = (area A + area C) – (area B – area C) = area A – area B

Indicated Power Indicated power: where N – crankshaft speed in rev/s nR – number of crank revolutions per cycle = 2 for 4-stroke = 1 for 2-stroke Power can be increased by increasing: the engine size, Vd compression ratio, rc engine speed, N

Indicated Work at Part Throttle At WOT the pressure at the intake valve is just below atmospheric pressure, However at part throttle the pressure is much lower than atmospheric Pint Therefore at part throttle the pump work (area B+C) can be significant compared to gross indicated work (area A+C)

Indicated Work with Supercharging Engines with superchargers or turbochargers can have intake pressures greater than the exhaust pressure, giving a positive pump work Pint Wi,n = area A + area B Supercharges increase the net indicated work but is a parasitic load since they are driven by the crankshaft

Mechanical Efficiency Some of the power generated in the cylinder is used to overcome engine friction and to pump gas into and out of the engine. The term friction power, , is used to collectively describe these power losses, such that: Friction power can be measured by motoring the engine. The mechanical efficiency is defined as:

Mechanical Efficiency (2) Mechanical efficiency depends on throttle position, engine design and engine speed. Typical values for car engines at WOT are: 90% @2000 RPM and 75% @ max speed. Throttling increases pumping work and thus decreases the brake power so the mechanical efficiency drops and approaches zero at idle. Power varies with speed but torque is “independent” of engine speed

Power and Torque versus Engine Speed Rated brake power There is a maximum in the brake power versus engine speed called the rated brake power (RBP). At higher speeds brake power decreases as friction power becomes significant compared to the indicated power 1 kW = 1.341 hp There is a maximum in the torque versus speed called maximum brake torque (MBT). Brake torque drops off: at lower speeds do to heat losses at higher speeds it becomes more difficult to ingest a full charge of air. Max brake torque

Indicated Mean Effective Pressure (IMEP) imep is a fictitious constant pressure that would produce the same work per cycle if it acted on the piston during the power stroke. imep does not depend on engine speed, just like torque imep is a better parameter than torque to compare engines for design and output because it is independent of engine speed, N, and engine size, Vd. Brake mean effective pressure (bmep) is defined as:

The maximum bmep of good engine designs is well established: Four stroke engines: SI engines: 850-1050 kPa* CI engines: 700 -900 kPa Turbocharged SI engines: 1250 -1700 kPa Turbocharged CI engines: 1000 - 1200 kPa Two stroke engines: Standard CI engines comparable bmep to four stroke Large slow CI engines: 1600 kPa *Values are at maximum brake torque at WOT Note, at the rated (maximum) brake power the bmep is 10 - 15% less Can use above maximum bmep in design calculations to estimate engine displacement required to provide a given torque or power at a specified speed.

Maximum BMEP The maximum bmep is obtained at WOT at a particular engine speed Closing the throttle decreases the bmep For a given displacement, a higher maximum bmep means more torque For a given torque, a higher maximum bmep means smaller engine Higher maximum bmep means higher stresses and temperatures in the engine hence shorter engine life, or bulkier engine. For the same bmep 2-strokes have almost twice the power of 4-stroke

Typical 1998 Passenger Car Engine Characteristics Vehicle Engine type Displ. (L) Max Power (HP@rpm) Max Torque (lb-ft@rpm) BMEP at Max BT (bar) Rated BP Mazda Protégé LX L4 1.839 122@6000 117@4000 10.8 9.9 Honda Accord EX 2.254 150@5700 152@4900 11.4 10.4 Millenia S Turbo 2.255 210@5300 210@3500 15.9 15.7 BMW 328i L6 2.793 190@5300 206@3950 12.6 11.5 Ferrari F355 GTS V8 3.496 375@8250 268@6000 13.1 11.6 456 GT V12 5.474 436@6250 398@4500 12.4 Lamborghini Diablo VT 5.707 492@7000 427@5200 12.7 11.0

Just some part of energy from Fuel are available at engine shaft.

Energy Distribution