7.3 Internal combustion engine

The internal combustion engine revolutionized transportation in the Modern Period. By converting chemical energy from fuel into mechanical power through controlled explosions, these engines transformed society and industry.

Understanding the principles of internal combustion provides insight into technological progress. From four-stroke cycles to fuel injection systems, advancements in engine design improved efficiency, power output, and environmental impact throughout the era.

Principles of internal combustion

• Internal combustion engines revolutionized transportation and industry during the Modern Period, powering vehicles and machinery
• These engines convert chemical energy from fuel into mechanical energy through controlled explosions within enclosed chambers
• Understanding internal combustion principles provides insight into the technological advancements that shaped modern society

Four-stroke cycle

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• Consists of intake, compression, power, and exhaust strokes
• Intake stroke draws fuel-air mixture into cylinder as piston moves downward
• Compression stroke compresses mixture as piston moves upward
• Power stroke ignites compressed mixture, forcing piston downward
• Exhaust stroke expels burned gases as piston moves upward again

Two-stroke cycle

• Completes power cycle in two piston movements (one revolution)
• Combines intake and compression into one stroke
• Merges power and exhaust into second stroke
• Offers higher power-to-weight ratio than four-stroke engines
• Used in smaller engines (chainsaws, motorcycles)

Compression ratio

• Measures volume of combustion chamber at bottom of piston stroke compared to top
• Higher compression ratios increase engine efficiency and power output
• Typical gasoline engines have compression ratios between 8:1 and 12:1
• Diesel engines operate at higher compression ratios (14:1 to 25:1)
• Limited by fuel octane rating to prevent engine knock

Fuel injection vs carburetion

• Fuel injection systems precisely meter fuel directly into engine cylinders or intake ports
• Carburetors mix fuel and air before entering the engine using venturi effect
• Fuel injection offers better fuel economy, emissions control, and performance
• Electronic fuel injection systems use sensors and computer control for optimal fuel delivery
• Carburetors simpler and less expensive, but less efficient and precise

Engine components and design

• Engine design evolved significantly during the Modern Period, improving efficiency and performance
• Component arrangement and materials advanced to meet increasing demands for power and reliability
• Understanding engine components provides insight into the complexity of modern machinery

Cylinder and piston arrangement

• Inline configuration aligns cylinders in a single row (inline-4, inline-6)
• V-configuration arranges cylinders in two banks at an angle (V6, V8)
• Flat or boxer engines have horizontally opposed cylinders
• Radial engines arrange cylinders in a circular pattern around crankshaft
• Number of cylinders affects engine smoothness, power output, and fuel efficiency

Valves and camshafts

• Valves control intake of fuel-air mixture and exhaust of combustion gases
• Camshafts actuate valves using lobes that push on valve stems or rockers
• Overhead valve (OHV) design places valves in cylinder head, camshaft in engine block
• Overhead cam (OHC) design places camshaft(s) directly above valves in cylinder head
• Variable valve timing systems adjust valve operation for improved performance and efficiency

Crankshaft and connecting rods

• Crankshaft converts reciprocating motion of pistons into rotational motion
• Connecting rods link pistons to crankshaft, transferring force from combustion
• Crankshaft design affects engine balance, smoothness, and power delivery
• Counterweights on crankshaft reduce vibration and improve engine balance
• Materials like forged steel or cast iron used for strength and durability

Fuel delivery systems

• Direct injection sprays fuel directly into combustion chamber
• Port fuel injection delivers fuel into intake port before intake valve
• Common rail systems in diesel engines maintain high fuel pressure for precise injection
• Mechanical fuel pumps used in older carbureted engines
• Electronic fuel pumps provide consistent fuel pressure for modern injection systems

Fuel types and efficiency

• Fuel technology advanced rapidly during the Modern Period, impacting engine design and performance
• Efficiency improvements reduced fuel consumption and environmental impact
• Understanding fuel types and efficiency helps explain the evolution of transportation and energy use

Gasoline vs diesel engines

• Gasoline engines use spark ignition to initiate combustion
• Diesel engines use compression ignition, relying on high pressure to ignite fuel
• Gasoline engines operate at lower compression ratios and higher RPMs
• Diesel engines offer higher torque and fuel efficiency but produce more emissions
• Gasoline engines generally smoother and quieter than diesel counterparts

Alternative fuels

• Ethanol produced from corn or sugarcane, often blended with gasoline
• Biodiesel derived from vegetable oils or animal fats, used in diesel engines
• Compressed natural gas (CNG) burns cleaner than gasoline or diesel
• Hydrogen fuel cells generate electricity through chemical reaction, producing only water vapor
• Liquefied petroleum gas (LPG) used in some vehicles, offers lower emissions than gasoline

Fuel economy considerations

• Engine size and configuration impact fuel consumption
• Aerodynamics of vehicle design affect fuel efficiency at higher speeds
• Tire rolling resistance influences fuel economy, especially at lower speeds
• Weight reduction improves fuel efficiency across all driving conditions
• Driving habits and maintenance practices significantly impact real-world fuel economy

Emissions and environmental impact

• Carbon dioxide (CO2) primary greenhouse gas produced by combustion engines
• Nitrogen oxides (NOx) contribute to smog formation and acid rain
• Particulate matter from diesel engines linked to respiratory health issues
• Catalytic converters reduce harmful emissions by converting pollutants
• Increasingly stringent emissions regulations drive development of cleaner engine technologies

Ignition and combustion process

• Ignition and combustion processes underwent significant refinement during the Modern Period
• Advancements in ignition systems improved engine efficiency and reliability
• Understanding these processes reveals the complexity of controlling energy release in engines

Spark ignition systems

• Distributor-based systems use mechanical timing to distribute spark to cylinders
• Distributorless ignition systems use individual coils for each cylinder or pair of cylinders
• Coil-on-plug systems place ignition coil directly on each spark plug
• Electronic ignition modules control spark timing based on engine conditions
• High-energy ignition systems provide stronger spark for more complete combustion

Compression ignition in diesel

• Relies on high compression ratios to heat air sufficiently to ignite fuel
• Glow plugs used to preheat combustion chamber for cold starts
• Injection timing critical for controlling combustion process and emissions
• Higher compression ratios result in greater thermal efficiency than spark ignition
• Produces characteristic diesel knock sound due to rapid pressure rise

Timing and engine knock

• Spark timing advances or retards to optimize combustion based on engine load and speed
• Knock sensors detect abnormal combustion, allowing ECU to adjust timing
• Pre-ignition occurs when fuel ignites before spark plug fires
• Detonation happens when end gases ignite after normal combustion front
• Octane rating measures fuel's resistance to knock and pre-ignition

Combustion chamber design

• Hemispherical chambers provide efficient combustion and valve placement
• Wedge-shaped chambers offer simplicity and good turbulence for mixing
• Pent-roof designs balance performance and emissions control
• Bowl-in-piston chambers used in direct injection diesel engines
• Squish areas in chamber promote turbulence for better fuel-air mixing

Power output and performance

• Engine power and performance increased dramatically during the Modern Period
• Advancements in design and materials allowed for higher outputs from smaller engines
• Understanding power output concepts helps explain the evolution of vehicle performance

Horsepower vs torque

• Horsepower measures rate of work done by engine
• Torque represents rotational force produced by engine
• Horsepower calculated as (torque × RPM) / 5252
• Peak horsepower typically occurs at higher RPMs than peak torque
• Torque important for acceleration and towing, horsepower for top speed

Engine displacement

• Total volume swept by all pistons in engine cylinders
• Measured in liters, cubic inches, or cubic centimeters
• Larger displacement generally produces more power and torque
• Smaller displacement engines often more fuel-efficient
• Forced induction allows smaller displacement engines to produce high power

Forced induction techniques

• Turbochargers use exhaust gases to drive compressor, increasing intake air pressure
• Superchargers mechanically driven by engine, providing immediate boost
• Intercoolers cool compressed air, increasing density for more power
• Twin-turbo setups use two smaller turbos for quicker response
• Variable geometry turbos adjust vane angle for optimal performance across RPM range

Power-to-weight ratio

• Measures engine power output relative to vehicle weight
• Higher ratio indicates better acceleration and overall performance
• Lightweight materials (aluminum, carbon fiber) improve power-to-weight ratio
• Important factor in racing and high-performance applications
• Electric motors offer high power-to-weight ratios due to instant torque

Cooling and lubrication systems

• Effective cooling and lubrication became crucial as engine power increased in the Modern Period
• These systems ensure engine longevity and maintain optimal performance
• Understanding cooling and lubrication provides insight into engine efficiency and reliability

Air-cooled vs liquid-cooled engines

• Air-cooled engines use fins on cylinder and head to dissipate heat
• Liquid-cooled engines circulate coolant through engine and radiator
• Air-cooled systems simpler, lighter, but less efficient at high power outputs
• Liquid-cooled engines maintain more consistent operating temperatures
• Air-cooled designs common in motorcycles and small engines, liquid-cooling dominates in automobiles

Radiator and coolant circulation

• Radiator transfers heat from coolant to air passing through its fins
• Water pump circulates coolant through engine and radiator
• Thermostat regulates coolant flow to maintain optimal engine temperature
• Coolant mixture typically contains water and ethylene glycol for freeze protection
• Overflow tank accommodates coolant expansion and contraction with temperature changes

Oil types and viscosity

• Mineral oils derived from crude oil, less refined than synthetic oils
• Synthetic oils offer better temperature stability and longevity
• Viscosity ratings (10W-30) indicate oil flow characteristics at low and high temperatures
• Higher viscosity oils provide better protection at high temperatures
• Lower viscosity oils reduce friction and improve fuel economy

Lubrication system components

• Oil pump circulates oil through engine passages and bearings
• Oil filter removes contaminants from circulating oil
• Oil pan serves as reservoir for engine oil
• Pressure relief valve prevents excessive oil pressure at high RPMs
• Oil cooler reduces oil temperature in high-performance applications

Engine management systems

• Engine management systems became increasingly sophisticated during the Modern Period
• These systems optimize engine performance, efficiency, and emissions control
• Understanding engine management reveals the complexity of modern automotive technology

Electronic control units (ECUs)

• Central computer controlling various engine functions
• Processes inputs from multiple sensors to adjust engine parameters
• Controls fuel injection, ignition timing, and other systems
• Stores diagnostic trouble codes for maintenance and repair
• Allows for adaptive learning to optimize performance over time

Sensors and actuators

• Mass airflow sensors measure incoming air volume
• Oxygen sensors monitor exhaust gases for optimal fuel mixture
• Knock sensors detect abnormal combustion
• Throttle position sensors track accelerator pedal movement
• Actuators control various components (fuel injectors, throttle body) based on ECU commands

Fuel mapping and tuning

• Fuel maps stored in ECU determine fuel injection quantity and timing
• 3D maps account for engine load, RPM, and other factors
• Tuning involves adjusting these maps for performance or efficiency
• Closed-loop systems use oxygen sensor feedback to fine-tune fuel delivery
• Open-loop operation occurs during cold starts or full throttle conditions

Onboard diagnostics

• OBD-II standard implemented in 1996 for consistent diagnostic protocols
• Monitors emissions-related systems and components
• Illuminates check engine light when faults detected
• Allows technicians to retrieve diagnostic trouble codes
• Supports real-time data streaming for advanced diagnostics

Advancements in engine technology

• Engine technology progressed rapidly during the Modern Period, improving performance and efficiency
• Innovations addressed challenges of power output, fuel economy, and emissions control
• Understanding these advancements shows the ongoing evolution of internal combustion engines

Hybrid engine systems

• Combine internal combustion engine with electric motor(s)
• Parallel hybrids can run on engine, electric motor, or both
• Series hybrids use engine solely to generate electricity for electric drive
• Plug-in hybrids allow battery charging from external power source
• Regenerative braking captures kinetic energy to recharge batteries

Variable valve timing

• Adjusts valve opening and closing times based on engine conditions
• Improves power output across RPM range
• Enhances fuel efficiency by optimizing intake and exhaust flow
• Reduces emissions by controlling exhaust gas recirculation
• Systems include VTEC (Honda), VVT-i (Toyota), and VANOS (BMW)

Direct fuel injection

• Sprays fuel directly into combustion chamber at high pressure
• Allows for precise control of fuel quantity and timing
• Improves fuel atomization for more complete combustion
• Enables stratified charge operation for lean-burn efficiency
• Reduces fuel consumption and emissions compared to port injection

Turbocharging and supercharging

• Forced induction systems increase engine power output
• Turbochargers use exhaust gas energy to drive compressor
• Superchargers mechanically driven by engine, providing instant boost
• Twin-scroll turbos separate exhaust pulses for improved efficiency
• Electric superchargers offer quick response without parasitic losses

Environmental regulations and future

• Environmental concerns became increasingly important during the Modern Period
• Regulations drove significant changes in engine design and technology
• Understanding these regulations and future trends reveals the ongoing evolution of transportation

Emission standards worldwide

• US EPA establishes federal emissions standards for vehicles
• European Union sets progressively stricter Euro emissions standards
• California Air Resources Board (CARB) often leads with stricter requirements
• Japan and other countries implement similar tiered emissions regulations
• Standards typically target reductions in CO, NOx, hydrocarbons, and particulate matter

Catalytic converters and filters

• Three-way catalytic converters reduce CO, HC, and NOx emissions
• Diesel particulate filters (DPF) trap soot particles from exhaust
• Selective catalytic reduction (SCR) uses urea injection to reduce NOx
• Gasoline particulate filters (GPF) emerging for direct injection engines
• Catalysts use precious metals (platinum, palladium, rhodium) to facilitate reactions

Electric vs combustion engines

• Electric vehicles produce zero tailpipe emissions
• Battery electric vehicles (BEVs) rely solely on stored electrical energy
• Fuel cell vehicles use hydrogen to generate electricity onboard
• Internal combustion engines still dominate due to infrastructure and range
• Hybrid systems bridge gap between conventional and fully electric powertrains

Future of internal combustion

• Continued development of more efficient combustion processes
• Integration of mild hybrid systems to improve efficiency and performance
• Exploration of low-carbon and carbon-neutral synthetic fuels
• Potential for hydrogen combustion engines as alternative to fuel cells
• Gradual phase-out in some markets due to stricter emissions regulations and electrification push