Transcript Slide 1
Engine Terminology Measuring Engine Performance Lesson 7 March 2008 Definition of Engine Torque Turning or twisting force that causes a body to turn (rotate). Torque = Length x Force Applied Engine torque is a rating of the turning force (torque) at the crankshaft end. Engine torque specifications can be found in shop manuals. Engine Torque Specs Given in a shop manual Torque 450 specification example: ft lb @ 3000 rpm engine would be capable of producing a maximum of 450 ft lb of torque at an operating speed of 3000 revolutions per minute The (N•m) metric unit for engine torque is newton-meters Definition of Horsepower Horsepower is the rate at which torque is produced. One horsepower is equal to 33,000 footpounds of work in one minute. One horsepower is equal to 746 watts, 545 Btu, 1055 joules, or 252 gram-calories. 1 HP is equal to 33,000 ft.lbs. of Work Horsepower Formula Remember laws of mechanics (physics) work = Distance (ft.) Moved x Force (lbs.) Applied Horse power example BHP & IHP BHP – Brake Horsepower usable power at the engine crankshaft IHP – Indicated Horsepower power formed in the combustion chamber There is a third HP rating that is important **WARNING** Horse Power Loss Friction and Load (HP robbers) Can you describe the difference between friction and load? Engine Friction What are the components that cause engine friction? Engine Load What components cause engine load? Does it not take horse power to drive these accessories? FHP (Frictional Horse Power) The power needed to overcome engine friction and load IHP (Indicated Horse Power) _ FHP (Frictional Horse Power) = BHP (Brake Horse Power) Efficiency How efficient is the four stroke cycle engine? 5% loss to engine friction and load 2 % chassis and transaxle weight 3 % tire resistance 2 % loss to aerodynamics 35 % Cooling system 35 % Exhaust system 20 % or less to do work .80 cents of every dollar thrown away Designed Loss of Efficiency Do you remember our discussion about engine friction and load? Now you can see the impact they have on efficiency. 2 Greatest Wastes of Power? Exhaust System 35% Cooling System 35% Thermal Efficiency Thermal efficiency is the measured comparison between horsepower output in relation to the amount of fuel burned to create this power. To look at it differently, thermal efficiency is the measurement of how well the engine uses the energy (heat) produced from combustion (burning fuel charge) to turn the crankshaft. Normal rating is 20-30 %. Keep the Heat In general, less heat rejected to the cooling system or atmosphere results in more heat energy to be converted to mechanical energy Exhaust coatings and wraps Coated piston crowns FHP / NHP /GHP /THP NHP – Net Horsepower – maximum power developed by an engine when all accessories on GHP – Gross Horsepower – maximum power developed with only minimum accessories on THP – Taxable Horsepower – rating of engine size Formula thp = bore squared x number of cylinders x .04 Reducing Friction Low tension piston rings Thinner piston rings Low tension valve springs Lighter valves allow lower tension valve springs Low-friction coatings Main and rod bearings Piston skirts Cam lobes and followers Mechanical Efficiency Mechanical efficiency compares the difference between Brake Horsepower (BHP) and Indicated Horsepower (IHP). If 70-80% mechanical efficiency is normal, then the lost horsepower was caused by our horsepower thieves and Frictional Horsepower. FHP(frictional) = IHP(indicated) – BHP(brake) Example : 30 (IHP) – 25(BHP) = 5 FHP Engine Efficiency Engine efficiency is the ratio of BHP (Brake Horsepower) to the power produced by the burning of a fuel charge (combustion) in the engine cylinders. BHP in relation to Fuel quantity = Engine efficiency As previously seen, only an average of 20% heat energy is available to do work (turning crankshaft). Engine Dynometer • measuring engine performance without driveline frictional losses Chassis Dynometer Measures the horsepower delivered to the rear wheels Indicates the amount of horsepower available to propel the car Accounts for any power consumed by the drive train Dyno Performance Chart Example of Engine Rating 2.0 liter 150 @ 6,400 rpm Engine HP (Dodge.com) 141 @ 5,200 rpm 135 @ 5,200 rpm Lb-Ft