M.S Ramaiah School of Advanced Studies - Bangalore. Session Objectives

Transcription

1 Automotive Engines Lecture delivered by: Prof. Ashok C.Meti MSRSAS-Bangalore 1 Session Objectives To understand the classification of automotive engines. Study the constructional features and arrangement of various parts of IC engines. Discus the new developments to improve the low-end performance of an engine Understand the lubrication system and cooling system of an IC engine 2 1

2 Topics Introduction to automotive engines 4S, Petrol and Diesel engines Main engine components Cooling system Lubrication system 3 Introduction to Automotive Engines An automotive engine is a complex piece of precision-built machinery. It provides power to drive the vehicle s wheels. In addition, it is also a source of power to other sub-systems like- charging, a/c unit, hydraulic system for power steering, suspension, etc. The engines used in automobiles are also known as internal combustion engines as the burning of air and fuel mixture takes place inside the cylinder. Ex: The mhawk Engine 4 2

3 Engine classification Some engine classifications include: Cylinder arrangement In-line*, V engine, opposed piston / flat engine Type of fuel burned Diesel* Petrol CNG / LPG Dual fuel engine Type of ignition Compression ignition* Spark ignition Number of strokes / cycle 4 stroke cycle* 2 stroke cycle Cooling system type Water cooled engine* Air cooled engine Type of aspiration Naturally aspirated engine Turbo* / super charged engine Number of valve / cylinder 2 valves per cylinder* Multi valve engines Valve location L head engine I head engine ( OHV)* Camshaft location Overhead cam engine Cam in the block engine* Combustion chamber design Shapes: Pancake, wedge, hemispherical, pent roof, precombustion chamber 5 In-line Engines 6 3

4 V- Engines 7 Horizontally Opposed PORSCHE 911 Carrera flat 6, 3.8 Lt. 283 kw (380bhp), DFI 120bar multiple injection (at high load and speed<3500rpm), CR 12.5:1, 7 speed DCT,2W/4W, 0-100kmph in 4.3s, VarioCam+ Valve system, 8 4

5 Four Stroke Petrol Engine Operation 9 Four-stroke cycle: Diesel Engine The four strokes of the engine operation requires 2 rotations of the crankshaft. 1Id 1. Induction Stroke Starting from TDC, the piston moves downwards. The inlet valve also opens at the same time and air is drawn into cylinder with out restriction by a throttle valve. When the piston reaches the BDC, the cylinder capacity is the largest. 10 5

6 2. Compression stroke The inlet and exhaust valves are closed. The piston s upward movement compresses the air to the degree determined dby the compression ratio (16:1 to 24:1). The air, in this process, heats up to C. Near the completion of the compression stroke, the fuelinjection system injects the fuel at high pressure (as much as 2000 bar in modern engines) in to hot compressed air in the CC. When the cylinder reaches the TDC, the cylinder capacity is at its minimum Ignition stroke After the ignition lag (a few degrees of C/s rotation) the ignition stroke begins. The finely atomized and easily combustible diesel fuel spontaneously ignites and burns. As a result, the cylinder charge heats up even more and pressure in the cylinder rises. The mass of the fuel injected (quality based control) determines the amount of energy released. The pressure forces the piston downwards. The C/s drive translates the KE of the piston into torque. 12 6

7 4. Exhaust stroke Just before the piston reaches the BDC, the exhaust valve opens. The hot pressurized gases flow out of the cylinder. The upwards movement of the piston forces the remaining exhaust gas out of the cylinder

8 Piston Assembly The piston converts the potential energy of the combustion gases, into the kinetic energy that turns the crankshaft. The piston is a cylindrical shaped hollow part that moves up and down inside the engine's cylinder. It has grooves around its perimeter near the top where rings are placed. The wrist pin connects the piston to the connecting rod. The connecting rod comes up through the bottom of the piston. The wrist pin is inserted into a hole (b (about half hlf way up) )h that goes through h the side of the piston, where it is attached to the connecting rod. Pistons are usually made of aluminum alloy, because it is light and a good heat conductor. Diesel Engine Piston Petrol Engine Piston 15 Pistons perform several functions. Transmit the driving force of combustion to the crankshaft. This causes the crankshaft to rotate. Also acts as a moveable gas-tight plug that keeps the combustion in the cylinder. Acts as a bearing for the small end of the connecting-rod. The piston head or "crown" is the top surface against which the explosive force is exerted. It may be flat, concave, convex or any one of a great variety of shapes to promote turbulence or help control combustion. 16 8

9 Crank Shaft The crankshaft converts the reciprocating motion of the pistons into a turning (rotary) motion. The crankshaft is usually either alloy steel or cast iron. The crankshaft is connected to the pistons by the connecting-rods. Some parts of the shaft do not move up and down; they rotate in the stationary main bearings. These parts are known as journals. There are usually five journals in a four cylinder engine 17 Engine Block Typical Cummins Engine Block A metal casting containing the cylinders and cooling ducts of an engine. All other sub-systems are bolted to the block. Cast Iron or Aluminum alloys are used to build the blocks. 18 9

10 Cylinder sleeves or liners They are inserts that fit into the cylinder block They act as cylinder walls for the piston to reciprocate Many vehicles use aluminum or CI cylinder blocks with cast iron, wet sleeves 19 Engine Head The cylinder head is the metal part of the engine that encloses and covers the cylinders. Bolted on to the top of the block, the cylinder head contains combustion chambers (petrol engine), water jackets and valves (in overhead-valve engines). The head gasket seals the passages within the head-block connection, and seals the cylinders as well. Typical Diesel Engine Heads M.S Ramaiah Typical School Petrol Engine of Advanced HeadStudies - Bangalore 20 10

11 Diesel combustion chambers Indirect Injection: In indirect injection, the fuel is injected into a separate chamber that is connected to the main chamber above the piston by a narrow passage-way. When the piston rises toward top-dead-center, the air is forced through the connecting passage at thigh hvelocity into the small chamber, called a swirl ilchamber. The high velocity air rotates at high velocity in the chamber as fuel is injected. A glow plug inserted into the chamber helps during cold starting. This type of system relies on the high velocity air swirl to mix the air so the fuel injection system can operate at lower pressures and be less expensive. After the fuel ignites, the combusting mixture pushes back out through the passage-way where the rise in pressure does work on the piston. 21 Direct Injection: In the direct injection diesel engine, the fuel is sprayed into the combustion chamber directly above the piston. The piston usually has a recess or bowl that is designed to confine the air into a region that matches the fuel spray trajectory. This type of system relies primarily on the momentum of the fuel spray to mix the fuel and air. The indirect injection (IDI) engine is less efficient than the direct injection (DI) engine. This is because the high velocity air motion in the combustion chamber causes high heat transfer rates resulting in greater loss of fuel energy

12 Valve Train The valve train consists of the valves and a mechanism that opens and closes them. The opening and closing system is made up of a camshaft and rocker arms. The camshaft has lobes on it that move the valves up and down. Diesel Engine Cam shaft Poppet valves 23 Common valve mechanisms Overhead cam engine with OHV Valve in block or L-head Cam-in-block / I head (pushrod valve M/sm 24 12

13 Valve Timing Diagram Petrol Engine (Advanced inlet gives more top end power at the expense of low end power, and vice-versa) 25 Valve Timing Diagram Diesel Engine SOC- start of combustion IO- Inlet open IC- Inlet close IP- Injection point EO-Exhaust open EC-Exhaust close 26 13

14 Flywheels A flywheel is bolted to the crankshaft flange The flywheel is also fitted with a ring ggear to which the starter pinion meshes while cranking the engine using starter. The clutch cover with the clutch disc are bolted to the flywheel. In certain diesel engines used on light vehicle, the flywheel will be replaced with a DMF for smoother, vibration free operation. 27 Engine Cooling System 28 14

15 Cooling System: Introduction In a typical gasoline engine, about 33% of the total heat input is lost to the coolant. The cooling system is responsible for dissipating this heat to the atmosphere The cooling system used in engines can be Liquid cooled system used in engines used in cars and trucks Air cooled system used in smaller engines like twowheelers Heat loss in an engine 29 Functions of cooling system Cooling system has several functions: Removing excess heat from engine The combustion of the fuel produces tremendous amount of heat Combustion flame temperatures can reach approx 2500 degree Centigrade- enough to melt the metal parts Part of this is removed by the cooling system fluid to protect the metal parts from damage Maintaining a constant operating temperature Engine operating temperature is the temperature the engine coolant reaches under normal running conditions Typically, an engine s operating temperature is in the range of degree Centigrade This temperature ensures that all part clearances are correct after expansions. Also ensures proper combustion, emission output levels and engine performance Increase the temperature of a cold engine quickly An engine must warm up rapidly to prevent poor combustion,,p part wear, oil contamination, reduced fuel economy, increased emissions and other problems. Too much of clearances Oil in a cold engine can be thick- increased wear Improper vaporization of fuel improper combustion Provide a means for warming the passenger compartment A cooling system commonly circulates coolant to the vehicle s heater. The engine coolant is warm, its heat can be used to warm the passenger compartment

16 Liquid cooling system Circulates coolant (a solution of water and cooling fluid) through water jackets. The coolant then collects excess heat and carries it out of the engine Liquid cooling: more precise control of the engine temperature Less temperature variations in side the engine Better temperature control leading to reduced ehaust emissions Improved heater operation for warming the passenger space Engine water jackets 31 Coolants Ethylene glycol based engine coolant concentrate 40 to 70 percent concentration in water Effective during both winter and summer in automotive vehicle cooling systems to provide protection against freezing, boiling and corrosion. A typical coolant fluid used in cooling system consists essentially of: ethylene glycol corrosion inhibitors, a foam suppressor, sufficient water to dissolve the additives Can be poured at temperatures as low as zero degrees degrees C

17 Cooling system components Conventional coolant flow type 33 Water pump: A centrifugal pump forces coolant through the engine block, cylinder head, intake manifold, hoses and radiator It is often driven by engine crankshaft through belt Radiator Transfers coolant heat to the outside air Normally mounted in the front of the engine Consists: Radiator core Radiator tanks Radiator filler neck Transmission oil cooler Radiator drain cock Scorpio water pump 34 17

18 Radiator Types Availability of space generally dictates the choice of the radiator. Both cross flow and down flow radiators are used 35 Radiator Pressure Cap Closed system 36 18

19 Thermostat Senses engine temperature and controls the coolant flow through the radiator. It reduces the coolant flow when engine is cold and increases as the W ll t t th t t ti engines gets warmer Wax pellet type is commonly used. When heated, the pellet expands and pushes the valve open. As the pellet and the thermostat cool, the spring tension overcomes pellet expansion and dthe valve closes The rating of the thermostat is its operating temperature which is normally degree Centigrade Wax pellet type thermostat operation 37 Engine Lubrication System 38 19

20 Lubrication system functions Important functions of lubricating systems. The system: Reduces friction and wear and tear between moving parts Helps transfer heat away from engine parts Cleans the inside of the engine by removing contaminants (metal, dirt, plastic, rubber and other particles) Cuts power loss and increases fuel economy Absorbs shocks between moving parts to quiet engine operation and increase engine life 39 Engine Oil Classifications: American Petroleum Institute (API) API established a classification system for the designation of gasoline and diesel engine oils, which reflects the quality, performance, and suitability of the oils for various engines. These classifications arearrangedintotwo different groups, For automotive gasoline engine service For commercial diesel engine service. The former is listed in "S" or "Service" categories (*presently SA through SM) The later is listed in "C" or "Commercial" categories (*presently CA through CI-4 PLUS). # Energy conserving reduce friction, Friction modifiers and other additives. 1.5% / 2.7% 40 20

21 SAE Classification A higher viscosity oil is very thick and resists flow and vise versa SAE has established an oil viscosity classification system. It is a numeric rating in which higher the number, higher the viscosity. Single-viscosity oil: Rated and designated for a limited range of operating temperatures. Its viscosity is not stable as multiviscosity oil Multiviscosity oil: Will exhibit operating characteristics of a thin oil light oil when cold and a thicker, heavier oil when hot. Although single-viscosity oils are available, most engine oils are multiviscosity oils.ex: SAE 10W-30 To specify engine oil, both the API service designation and the SAE viscosity grade are required. 41 Components of Lubricating Systems Main components of a typical lubricating systems: Oil pump Oil pump pick-up Oil pan or sump Pressure relief valve Oil filter Engine oil passage or galleries Oil pressure indicator Dipstick Oil cooler 42 21

22 Typical heavy duty diesel engine lubrication circuit 43 Oil pump: Most commonly used oil pumps: Rotor type Gear type Both are positive displacement type pumps. The output volume is proportional to the speed of the pump. Pump is directly or indirectly driven by the cam shaft or a gear at the front of the crankshaft

23 Engine oil galleries: The oil galleries consist of interconnecting passages that have been drilled completely through the engine block during manufacturing. The oil is routed through these passages to various parts of the engine. The crankshaft also contains oil passages to route the oil from the main bearing to the connecting rod bearing surfaces. 45 Oil filters All the oil that leaves the pump is directed to the oil filter (Full-flow filter). This is to ensure that very small particles of dirt and metal carried by the oil will not reach the close-fitting engine parts. From filter, oil flows into engine s main oil gallery. Full-flow filtration system 46 23

24 Example: Commercial vehicle engine The combustion technology with 4 valve per cylinder and optimised fuel injection system helps in achieving the stringent BS III emissions without any after treatment and not even EGR system. The superior combustion technology enables to meet the futuristic emission norms of BSIV also without any aftertreatment like SCR or Catalytic convertors. Emissions Specifications 6.12TCA Euro III, capability for Euro IV Configuration 6, Inline 6, Inline Valves / Cylinder TCE Euro III, capability for Euro IV Displacement Lts Bore x Stroke mm 105 x x 137 Combustion system Direct Injection Direct Injection Injection system Mechanical Common Rail Power Output hp rpm (960 - Peak Torque kgf-m rpm Weight (Dry) kg Dimensions mm Length Width Height Summary The classification of IC engines based on various parameters, and engine applications have been explained. The constructional details of the main parts of an engine like piston assembly, block, head and valve mechanisms including the recent developments have been discussed. The lubrication system and cooling systems of an IC engine has been explained 48 24