internal combustion engines

INTERNAL COMBUSTION ENGINES




Energy: The ability of a physical system to do work on other physical systems. Heat: Heat is energy transferred from one body, region, set of components, or thermodynamic system to another in any way other than as work. OR Energy can be transferred as heat by thermal conduction, thermal radiation, friction and viscosity, and by chemical dissipation. Combustion: Combustion is a chemical reaction in which certain elements of the fuel combine with oxygen releasing a large quantity of energy causing an increase in temperature of gases.


Engine:

An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat Engine: Heat engines are devices used to produce net work from a supply of heat by operating in a cyclic manner. Heat engines differ considerably from one another, but all can be characterised by the following: 1-They receive heat from a high-temperature source (e.g., combustion chamber, solar energy, nuclear reactor). 2-They convert part of this heat to work (usually in the form of a rotating shaft). 3-They reject the remaining waste heat to a low-temperature sink (the atmosphere, rivers, etc.). 4-They operate in a cycle.


Classification of Heat Engine:

Heat Engines

Internal Combustion Engines

Reciprocating Engines e.g. Petrol Engine Diesel Engine

External Combustion Engines

Turbines

Reciprocating Engines

Turbines

e.g. Gas Turbines

e.g. Steam Engines

e.g. Steam Turbines

Stirling Engines


Internal Combustion Engines: -Combustion takes place directly in the working fluid and the expanding force of combustion is converted into mechanical force by means of a suitable mechanism. -The product of combustion of air and fuel is, directly, the motive or working fluid. External Combustion Engines: -Fuel burns outside the working fluid and the products of combustion transfer heat to a second fluid, which then becomes the motive or working fluid.


Reciprocating Engines: -Cycle consists of a succession of non-flow processes. -A given mass of working fluid can be taken through a series of processes in a cylinder fitted with a reciprocating piston. -Used for small power production. Turbines: -Cycle is a series of steady flow processes -Used to develop high power.


Thermal Efficiency: Thermal Efficiency = Net Work Output/Total Heat Input η = Wnet, out/Qin = 1-Qout/Qin The thermal efficiency of a heat engine is always less than unity. The Thermal Efficiencies of Work-Producing Devices: Ordinary spark-ignition automobile engine 25 % Diesel engines and large gas-turbine plants 35 % Steam power plants 40 % Large combined gas-steam power plants 50 %



1700-1860: Steam Engines were used. 1860: -Internal Combustion Engine became practical reality. -J.J.E. Lenoir developed first marketable engine in which coal-gas air mixture was burned at atmospheric pressure. -The double working engine had a cylinder. -On the way from one extreme to the middle of the cylinder, a fuel mixture gets sucked performing work on the piston after the ignition during the other half of the way. -On the other side, the discharge of the burned gas takes place at the same time. -Now the engine works in the opposite direction, using the same principle. Efficiency = 5%


1867: -Nicolaus A. Otto and Eugen Langen introduced an atmospheric engine. -The pressure was raised resulting from combustion of the fuel-air charge early in the outward stroke to accelerate a free piston and rack assembly so its momentum would generate a vacuum in the cylinder. -Atmospheric pressure then pushed the piston inward with the rack engaged through a roller clutch to the output shaft. -5000 units of this type were built and sold. -Efficiency = 11%


LENOIR ENGINE

OTTO & LANGEN ATMOSPHERIC ENGINE


1876: -Nicolaus A. Otto proposed an engine cycle with four piston strokes an intake, then compression before ignition, an expansion or power stroke where work was delivered to the crankshaft and finally an exhaust stroke. Otto and Langen Otto 4-Stroke -Brake Horsepower 2 2 -Weight (lbs) 4000 1250 -Piston Displacement (in3) 4900 310 -Power Strokes/min 28 80 -Shaft Speed (rpm) 90 160 -Overall Eff. (%) 11 14


1880s: -Several engineers successfully developed two-stroke internal combustion engine. 1892: -German Engineer Rudolf Diesel invented Diesel Engine doubling the efficiency over other internal combustion engines. 1957: -German inventor Felix Wankel introduced the rotary internal combustion engine. 1960s: -Emission Standards were introduced. 1990s: -Six stroke engine was invented.



1- Application: Automobile, Truck, Locomotive, Light Aircraft, Marine, Portable Power Systems, Power Generation. 2- Basic Engine Design: Reciprocating and Rotary.


3- Working Cycle: Four-Stroke Cycle: Naturally Aspirated, Supercharged and Turbocharged.


3- Working Cycle: Two-Stroke Cycle: Crankcase Scavenged, Supercharged and Turbocharged.


Air Standard Cycle: -Medium is air -No chemical reaction -Heat is supplied to the air and some heat is rejected from the air during the cycle -Specific heat of air is assumed to be constant -Losses by heat transfer through the cylinder walls are assumed to be zero Real Air-Fuel Engine Cycle: -Open cycle with changing composition -At inlet there is mixture of air and fuel which changes during combustion to a gas mixture of CO2, H2O, N2, CO & HC -Heat losses -Combustion requires a short but finite time to occur and heat addition is not instantaneous at TDC as approximated in an Otto cycle -Temperature and pressure rise before combustion is less than predicted by air-standard cycle because inlet valve does not close even at BDC to improve volumetric efficiency


Otto Cycle:


Otto Cycle (Air Standard-Ideal): 0-1: Intake 1-2: Adiabatic compression 2-3: Constant volume heat addition 3-4: Adiabatic expansion 4-1: Constant volume heat rejection 1-0: Exhaust Otto Cycle (Real Air-Fuel):


Constant Pressure Combustion Diesel Cycle :


Constant Pressure Combustion Diesel Cycle (Air Standard-Ideal): 0-1: Intake 1-2: Isentropic compression 2-3: Constant pressure heat addition 3-4: Isentropic expansion 4-1: Constant volume heat rejection 1-0: Exhaust Constant Pressure Combustion Diesel Cycle(Real Air-Fuel):


Limited Pressure Combustion Diesel Cycle:


Limited Pressure Combustion Diesel Cycle (Air Standard-Ideal): 0-1: Intake 1-2: Isentropic compression 2-2.5: Constant volume heat addition 2.5-3: Constant pressure heat addition 3-4: Isentropic expansion 4-1: Constant volume heat rejection 1-0: Exhaust Limited Pressure Combustion Diesel Cycle (Real Air-Fuel):

0


4- Valve or Port Design and Location: Overhead Valve:


4- Valve or Port Design and Location: Rotary Valve: -High rpm and ultimately high power -Compact and light weight cylinder head


4- Valve or Port Design and Location: Cross-Scavenged Porting: Inlet and exhaust ports on opposite sides of cylinder. Loop-Scavenged Porting: Inlet and exhaust ports on same side of cylinder. Uniflow-Scavenged: Inlet and exhaust ports or valves at different ends of cylinder.


5- Fuel: Gasoline (or petrol): -Mixture of many hydrocarbon components manufactured from crude petroleum. -It would have a molecular structure C8H15 if gasoline is approximated as single-component hydrocarbon fuel. Gasoline LHV = 43.45 MJ/kg (34.2 MJ/lit) Fuel Oil (or diesel oil): Light diesel: Approximated by the chemical formula C12.3H22.2, Less viscous and easier to pump. Heavy diesel: Approximated by the chemical formula C14.6H24.8, Used in larger diesel engines with higher injection pressures. Biodiesel: Obtained from renewable sources such as vegetable oil, animal fat, greases and recycled cooking oil. Diesel LHV = 42.79 MJ/kg (37.3 MJ/lit)


5- Fuel: Natural Gas: -Mixture of methane CH4 (60 to 98%) and other hydrocarbon fuel components -It is stored as compressed natural gas (CNG) at pressures 16 to 25 MPa or liquid natural gas (LNG) at pressures 70 to 210 kPa and -1600C CNG LHV = 47.14 MJ/kg (9.0 MJ/lit) LNG LHV = 48.63 MJ/kg (22.2 MJ/lit) Liquid Petroleum Gas (LPG): -Mixture of butane C4H10 and propane C3H8 -Obtained from crude oil associated with light hydrocarbons and methane rich gas LPG (Propane based) LHV = 46.61 MJ/kg (25.3 MJ/lit) LPG (Butane based) LHV = 45.28 MJ/kg (27.7 MJ/lit)


5- Fuel: Alcohols: -Obtained from corn, grains and organic waste -Methyl alcohol or methanol CH4O and ethyl alcohol or ethanol C2H6O Methanol HHV = 22.7 kJ/g Ethanol HHV = 29.7 kJ/g Hydrogen: -High energy content per unit mass. -Obtained from coal gasification or by electrolysis of water. Hydrogen LHV = 120.21 MJ/kg (0.01079 MJ/lit) Dual Fuel: Natural gas and diesel


6- Method of Mixture Preparation: Carburetion:


6- Method of Mixture Preparation: Fuel injection into the intake ports or intake manifold:


6- Method of Mixture Preparation: Fuel injection into the engine cylinder:


7- Method of Ignition: Spark ignition: In conventional engines where the mixture is uniform and in stratified-charge engines where the mixture is nonuniform. Stratified Charged Engines: -These engines combine the best features of the spark-ignition engine and the diesel engine. -The goal is to operate such an engine at close to the optimum compression ratio for efficiency (in the 12 to 15 range). Characteristics: 1- Fuel is injected directly into the combustion chamber to avoid knock 2-Igniting the fuel as it mixes with air with a spark plug 3-Controlling the engine power by varying the amount of fuel with the air flow unthrottled

Compression Ignition:


8- Combustion Chamber Design: Open Chamber: Wedge, Hemisphere, Bowl-in-piston etc.


8- Combustion Chamber Design: Divided Chamber: Small and large auxiliary chambers; many designs: e.g., swirl chamber, prechambers.


9- Method of Load Control: -Throttling of fuel and air flow together so mixture composition is essentially unchanged -Control of fuel flow alone -Combination of these 10- Method of Cooling: -Water Cooled -Air Cooled -Uncooled




1- Cylinder Block Material: Grey cast iron in larger engines because of its good wear resistance and low cost and aluminum in some smaller SI engine blocks Manufacturing Process: Casting


2- Cylinder Liner (Sleeve) a)-Wet Liner: Direct contact with coolant b)- Dry Liner: Indirect contact with coolant Material: Iron alloys Manufacturing Process: Casting -Block is heated and cold sleeve is pressed into it. -After cooling the cylinder shrink fits around the sleeve. -Boring and honing is done finally.


3- Cylinder Head Material: Cast iron or aluminum Manufacturing Process: Casting


4- Piston Material: Aluminum in small engines and cast iron in larger slower-speed engines Manufacturing Process: Casting


5- Piston Rings a)- Compression Rings: These provide seal between cylinder walls and piston and prevent leakage of burning gases b)- Oil Rings: These regulate oil film thickness on cylinder walls Material: Grey cast iron Manufacturing Process: Casting


6- Connecting Rod (Conrod) Material: Steel or alloy forging and sometimes aluminum in small engines Manufacturing Process: Forging and casting


7- Crankshaft Material: Steel Manufacturing Process: Forging


8- Camshaft Material: Cast iron or forged steel Manufacturing Process: Casting or forging


9- Valves Material: Forged alloy steel Manufacturing Process: Forging Cooling of exhaust valve is enhanced by using a hollow stem partially filled with sodium which through evaporation and condensation carries heat from hot valve head to cooler stem.


10- Oil Pan Material: Mild steel Manufacturing Process: Stamping


11- Gaskets Material: Plain copper sheets or steel sheets Manufacturing Process: Stamping and O-ringing O-ringing is a process of placing a piece of wire around the circumference of the cylinder to bite into the copper

O ringing

Engine Components



1- Air Induction System: Air Measurement Air Filter

Intake Manifold Intake of Atmospheric Air


2- Exhaust System:


3- Fuel Injection System: A)- SI Engines

Carburettor


3- Fuel Injection System: A)- CI Engines

Individual pump system

Pump element


4- Lubrication System:

Pressure-feed lubrication system


5- Engine Cooling System:

Pump circulating cooling system



Automobile (Passenger-carrying road vehicle): A road vehicle, usually with four wheels and powered by an internal-combustion engine, designed to carry a small number of passengers.

Complete Transmission

Clutch

Differential



1- Front-Wheel-Drive Layout: FF (Front-engine, front-wheel-drive layout) Advantages: 1- Increased space for passengers 2- Fewer components means lower weight 3- Improved fuel efficiency due to lower weight

4- Understeer 5- The direct connection between engine and transaxle reduces the mass and mechanical inertia of the drivetrain compared to a rear-wheel-drive vehicles.


1- Front-Wheel-Drive Layout: FF (Front-engine, front-wheel-drive layout) Advantages: 6- As the steered wheels are taking power directly from the engine, FF cars are generally considered superior to FR (frontengine, rear-wheel-drive layout) cars in conditions such as snow, mud, or wet tarmac. Disadvantages: 1- Powerful cars and racing cars rarely use the FF layout because weight transference under acceleration reduces the weight on the front wheels and reduces their traction, limiting the torque which can be utilized. 2- Uneven weight distribution 3- Increased turning circle 4- The FF layout restricts the size of the engine that can be placed in modern engine compartments.


2- Rear-Wheel-Drive Layout: FR (Front-engine, rear-wheel-drive layout) Advantages: 1- Even weight distribution 2- During heavy acceleration, weight is placed on the rear, or driving wheels, which improves traction

3- Smaller steering radius 4- Serviceability is easy


2- Rear-Wheel-Drive Layout: FR (Front-engine, rear-wheel-drive layout) Advantages: 5- Can accommodate more powerful engines as a result of the longitudinal orientation of the drivetrain, such as the Inline-6, 90° big-bore V8, V10 and V12 making the FR a common configuration for luxury and sports cars Disadvantages: 1- Oversteer under heavy acceleration 2- On snow, ice and sand, rear-wheel drive loses its traction advantage to front- or all-wheel-drive vehicles, which have greater weight on the driven wheels. 3- Decreased interior space 4- Increased weight 5- Higher initial purchase cost


3- Four-Wheel-Drive Layout (4WD): Advantages: 1- Traction is nearly doubled compared to a two-wheeldrive layout

Disadvantages: 1- 4WD systems require more machinery and complex transmission components, and so increase the manufacturing cost of the vehicle



1- SI Engines: Four Stroke Small Single Cylinder: a)- Home: Lawn mowers, chain saws etc b)- Portable power generation c)- Outboard motorboat engine d)- Motorcycles  Most important characteristics: Light weight, small bulk

and low cost Less important characteristics: Fuel consumption, engine vibration and engine durability


1- SI Engines:

Four Stroke Small Multicylinder: Automotive practice  Being small in size and light in weight it is advantageous to increase the number of cylinders per engine to meet the requirements of increased power.  Multicylinder engines achieve a better state of balance than single cylinder.  Four cylinder in-line up to about 2.5 liter displacement is most common


1- SI Engines:

Four Stroke V arrangement: Automotive practice  V-6, V-8 and V-12 arrangement are commonly used to provide compact, smooth, low vibration SI engine Turbocharged: Automotive practice:  To increase the maximum power that can be obtained from a given displacement engine


1- SI Engines: Two Stroke Small Single Cylinder: Outboard motorboat engines, motorcycles and chain saws etc.  Used where low cost and weight/power ratio are required features use factor is low Wankel Rotary Engine: Mazda car  Advantages: Compact, high speed (high power/weight and power/volume ratios), inherent balancing and smoothness  Disadvantages: High heat transfer, sealing and leakage problems


2- CI Engines: Two Stroke Very Large Engines: Marine and stationary power generation Example: -Large Sulzer (Wartsila Corporaiton, Finland) turbocharged marine diesel engine. Bore: 840 mm, Stroke: 2900 mm, Rated power: 1.9 MW per cylinder at 78 rev/min, 4 to 12 cylinder -Emma Maersk (Ship owned by Danish company Maersk) powered by world’s largest two-stroke turbocharged slow speed diesel engine, Wartsila RT-flex96C. 13.5 m high, 27.3 m long, weighs over 2300 tons, 14 cylinder, 81 MW at 14000 lit heavy fuel oil/hr. Air capacity is an important constraint therefore turbocharging is used extensively


Permanently moored in 2004 and scraped in 2010


2- CI Engines: Four Stroke Medium Engines: Trucks and buses  Turbocharged, direct injection Four Stroke Small Engines: Automobile  High speed, indirect-injection  Indirect-injection diesel engines require higher compression ratios than direct-injection to start when cold
