Internal Combustion Engines (ME-501) - Unit 2 Short Notes

I. THERMODYNAMIC CYCLES

A. Spark Ignition (SI) Engine Cycles

1. Ideal Otto Cycle

• Processes:

  1-2: Isentropic compression

  2-3: Constant volume heat addition

  3-4: Isentropic expansion

  4-1: Constant volume heat rejection

• Assumptions: Air as ideal gas, constant specific heats, no friction, reversible processes, no pressure drops.

• P-V and T-S Diagrams:

  DiagramSEARCH: Otto cycle PV TS diagram

• Air Standard Efficiency:

$$\eta = 1 - \frac{1}{r^{\gamma-1}}$$

where \(r\) = compression ratio, \(\gamma = C_p/C_v\).

• Work Output: \(W = Q_{in} - Q_{out} = C_v(T_3 - T_2) - C_v(T_4 - T_1)\).

2. Otto Cycle Calculations

• Given initial conditions (\(P_1, T_1\)), compression ratio \(r\), heat added \(Q_{in}\):

  • \(T_2 = T_1 r^{\gamma-1}\), \(P_2 = P_1 r^\gamma\)

  • \(T_3 = T_2 + Q_{in}/C_v\)

  • \(P_3 = P_2 (T_3/T_2)\) (constant volume)

  • \(T_4 = T_3 / r^{\gamma-1}\), \(P_4 = P_3 / r^\gamma\)

• Mean Effective Pressure (MEP):

$$MEP = \frac{W}{V_s} = \frac{Q_{in} \left(1 - \frac{1}{r^{\gamma-1}}\right)}{V_1 \left(1 - \frac{1}{r}\right)}$$

where \(V_s = V_1 - V_2\) (swept volume).

3. Actual Otto Cycle Deviations

• Variation of specific heats (\(\gamma\) decreases with temperature).

• Pressure drops in intake/exhaust manifolds.

• Heat transfer to cylinder walls.

• Friction and pumping losses.

[!TIP] In calculations, use absolute temperature (K) and consistent units.

B. Compression Ignition (CI) Engine Cycles

1. Ideal Diesel Cycle

• Processes:

  1-2: Isentropic compression

  2-3: Constant pressure heat addition

  3-4: Isentropic expansion

  4-1: Constant volume heat rejection

• P-V and T-S Diagrams:

  DiagramSEARCH: Diesel cycle PV TS diagram

• Cut-off ratio: \(\alpha = V_3 / V_2\).

2. Diesel Cycle Analysis

• Efficiency:

$$\eta = 1 - \frac{1}{r^{\gamma-1}} \left( \frac{\alpha^\gamma - 1}{\gamma(\alpha - 1)} \right)$$

• For same compression ratio \(r\) and same heat input, Otto cycle is more efficient because heat addition at constant volume yields higher average temperature.

3. Diesel Cycle Calculations

• Given \(r\), \(\alpha\), \(P_1, T_1\):

  • \(T_2 = T_1 r^{\gamma-1}\), \(P_2 = P_1 r^\gamma\)

  • \(T_3 = T_2 + Q_{in}/C_p\) (since constant pressure, \(P_3 = P_2\))

  • \(V_3 = \alpha V_2\), so \(T_3 = T_2 \alpha\) (from ideal gas law)

  • \(T_4 = T_3 / r^{\gamma-1}\)

  • Efficiency from formula above.

C. Dual Cycle (Mixed Cycle)

• Heat addition partly at constant volume (2-3) and partly at constant pressure (3-4).

• More realistic than Otto or Diesel alone.

• Efficiency lies between Otto and Diesel for same \(r\).

D. Cycle Comparisons

II. ENGINE CYCLE ANALYSIS AND PERFORMANCE PARAMETERS

A. Actual vs Ideal Engine Cycles

• Theoretical Valve Timing: Intake opens at TDC, closes at BDC; exhaust opens at BDC, closes at TDC.

• Actual Valve Timing:

  • Intake opens before TDC (lead), closes after BDC (lag).

  • Exhaust opens before BDC, closes after TDC.

  • Overlap period: Both valves open (intake and exhaust).

  DiagramSEARCH: actual valve timing diagram 4 stroke

• Causes of Deviation:

  • Flow losses (pressure drops in ports, valves).

  • Heat transfer to walls.

  • Friction and accessory drives.

B. Performance Parameters and Definitions

C. Engine Testing and Performance Calculation

1. Morse Test (for multi-cylinder engines)

• Method:

  1. Run all cylinders, measure BP\(_{all}\).

  2. Cut out one cylinder at a time, measure BP\(_i\) for remaining cylinders.

• Assumptions:

  • Friction power of each cylinder is identical.

  • Friction power of cut-out cylinder remains constant when cut.

• Calculations:

$$IP = \frac{n \cdot BP_{all} - \sum_{i=1}^{n} BP_i}{n-1}$$

$$\eta_m = \frac{BP_{all}}{IP}$$

where \(n\) = number of cylinders.

2. Heat Balance Sheet

• Energy Input: \(\dot{Q}_{in} = \dot{m}_f \times CV\) (kJ/min or kJ/s).

• Energy Output Distribution:

  • Brake Power (BP)

  • Heat to cooling water: \(\dot{Q}_w = \dot{m}_w C_{pw} \Delta T_w\)

  • Heat to exhaust gases: \(\dot{Q}_{ex} = \dot{m}_{ex} C_{pex} (T_{ex} - T_{amb})\)

  • Heat to radiation & unaccounted: \(\dot{Q}_{rad} = \dot{Q}_{in} - (BP + \dot{Q}_w + \dot{Q}_{ex})\)

• Preparation: All quantities on per minute or per second basis. Sum of outputs ≈ input (allow 5% error).

3. Performance Calculation from Trial Data

• Given: Torque \(T\), speed \(N\), fuel consumption \(\dot{m}_f\), air consumption \(\dot{m}_a\), cooling water data, exhaust gas data, calorific value \(CV\).

• Steps:

  1. \(BP = \frac{2\pi T N}{60}\)

  2. \(BSFC = \frac{\dot{m}_f}{BP}\)

  3. \(\eta_{bth} = \frac{BP}{\dot{m}_f CV}\)

  4. Heat balance as above.

III. COMBUSTION IN SPARK IGNITION (SI) ENGINES

A. Stages of Combustion (with Pressure-Crank Angle Diagram)

1. Ignition Delay (Lag):

   • Physical phase: Fuel atomization, vaporization, mixing with air.

   • Chemical phase: Pre-flame reactions (low-temperature oxidation).

2. Flame Propagation:

   • Initial stage: Flame kernel growth (0–10° after spark).

   • Main stage: Turbulent flame spread (10–80% of charge).

   • Afterburn: Combustion of remaining charge near walls.

3. Rates:

   • Rate of pressure rise: \(\frac{dp}{d\theta}\) (max during main combustion).

   • Rate of combustion: \(\frac{dQ}{d\theta}\).

B. Factors Affecting Flame Speed

• Turbulence/Swirl/Squish: Increase flame speed (turbulent flame speed \(S_T \gg\) laminar \(S_L\)).

• Compression ratio: Higher \(r\) → higher \(T, P\) → faster flame.

• Fuel-air ratio: Stoichiometric (\(\phi=1\)) gives maximum flame speed.

• Temperature & Pressure: Higher intake \(T, P\) increase flame speed.

C. Abnormal Combustion

1. Detonation/Knock

• Phenomenon: Spontaneous ignition of end gas ahead of flame front, causing high-frequency pressure waves ("pinging").

• Theories:

  • Thermal theory: Hot spots (e.g., carbon deposits) initiate combustion.

  • Pressure wave theory: Pressure waves compress end gas to auto-ignition.

  • Chemical theory: Low-temperature oxidation reactions.

• Effects: Power loss, overheating, piston damage, bearing failure.

2. Variables Affecting Detonation

• High compression ratio.

• Advanced ignition timing.

• Low octane rating fuel.

• High intake temperature/pressure.

• Carbon deposits in combustion chamber.

3. Pre-ignition

• Cause: Fuel ignites before spark (due to hot spots like glowing deposits, spark plug overheating).

• Difference from detonation: Pre-ignition occurs before spark; detonation after spark but abnormal.

• Remedy: Retard ignition timing, use higher octane fuel, clean deposits, select correct spark plug heat range.

4. Knock Comparison: SI vs CI

5. Control of Abnormal Combustion

• Fuel additives (tetraethyl lead, MTBE, aromatics).

• Design changes: swirl/tumble, squish, compact chamber.

• Ignition timing retardation.

• Cooling of intake charge.

D. Combustion Chamber Design for SI Engines

1. Desirable Characteristics

• Compact (short flame travel).

• High turbulence/swirl at TDC.

• Proper squish clearance (0.5–1.5 mm).

• No sharp corners (avoid hotspots).

2. Types of Combustion Chambers

• Shallow piston bowl: Simple, but moderate turbulence.

• Hemispherical (Hemi): Large valves, good breathing, high compression, but heavy.

• Wedge: Simple, good turbulence, used in American V8s.

• Pentroof: Modern, multi-valve, high turbulence, compact.

• Swirl/Tumble chambers: Pre-combustion chambers for high turbulence.

3. Shape Effects: Compact shape reduces knock; high turbulence increases flame speed, reduces knock tendency.

E. Ignition Systems

1. Ignition Lag: Decreases with higher intake temperature/pressure, turbulence, and advanced timing.

2. Spark Plug Requirements

• Heat range: Cold plug (fast heat transfer) for high-performance engines; hot plug for low-speed to avoid fouling.

• Gap: 0.6–1.2 mm (larger gap → stronger spark but higher voltage needed).

• Materials: Nickel, platinum, iridium (long life).

3. Battery Ignition System

• Construction: Battery → ignition switch → coil (primary/secondary) → distributor (points, capacitor) → spark plugs.

• Working: Points open/close primary current, inducing high voltage in secondary.

• Advantages: Simple, cheap.

• Disadvantages: Points wear, limited spark energy at high speed, maintenance.

4. Electronic Ignition: Transistor/contactless triggering, longer life, better spark, no maintenance.

IV. COMBUSTION IN COMPRESSION IGNITION (CI) ENGINES

A. Stages of Combustion

1. Ignition Delay Period:

   • Physical phase: Atomization, evaporation, mixing of fuel with air.

   • Chemical phase: Pre-flame reactions (low-temperature oxidation).

2. Rapid Combustion (Uncontrolled): Combustion of fuel accumulated during delay → rapid pressure rise.

3. Controlled Combustion (Diffusion): Fuel burns as it mixes with air (controlled by injection rate).

4. Afterburning: Late combustion near exhaust valve.

B. Factors Affecting Delay Period

• Fuel Properties:

  • Cetane number: Higher cetane → shorter delay.

  • Volatility & viscosity: Higher volatility → shorter delay.

• Engine Conditions:

  • Higher compression ratio → higher \(T, P\) → shorter delay.

  • Higher intake temperature/pressure → shorter delay.

  • Load: Higher load → higher \(T, P\) → shorter delay.

• Injection Parameters:

  • Start of injection timing (advanced → longer delay? Actually, advanced injection gives more time for mixing, but delay period itself may shorten with higher \(T, P\)).

  • Spray pattern & atomization: Better atomization → shorter delay.

C. Fuel Injection Systems

1. Functions:

• Metering: Correct quantity of fuel.

• Timing: Start and duration of injection.

• Atomization: Break fuel into fine droplets.

• Distribution: Proper spray pattern in cylinder.

2. Types of Injection Systems

• Air injection (obsolete): Air carries fuel into cylinder.

• Solid injection:

  • Common rail: High-pressure accumulator, electronically controlled injectors.

  • Unit injector: Pump and nozzle per cylinder, cam-driven.

  • Pump-line-nozzle: Inline or distributor pump, high-pressure lines, nozzle.

3. Fuel Injector (Nozzle)

• Construction: Body, needle valve, spring, orifice.

• Working: High-pressure fuel lifts needle, sprays through orifices.

• Types:

  • Hole type: Multiple holes, common in direct injection.

  • Pintle type: Pintle valve extends, better atomization, used in indirect injection.

  • Throttle type: For specific spray patterns.

D. Combustion Chambers for CI Engines

• Open chamber (direct injection): High compression ratio, efficient, requires high injection pressure.

• Pre-combustion chamber: Auxiliary chamber connected by orifice, easier starting, smoother.

• Swirl chamber: Auxiliary chamber with tangential entry, creates swirl, good mixing.

E. Diesel Knock

• Phenomenon: Violent noise due to sudden pressure rise when combustion starts after long delay.

• Relation to delay period: Longer delay → more fuel accumulated → faster combustion → higher pressure rise → more knock.

• Cetane number: Higher cetane → shorter delay → less knock.

V. FUEL SYSTEMS AND MIXTURE PREPARATION

A. Carburetion in SI Engines

1. Definition: Formation of homogeneous air-fuel mixture for SI engine.

2. Theory of Carburetion

• Based on Bernoulli's principle: Velocity increase → pressure drop.

• Venturi effect: Throat area \(A_t\), pressure drop \(\Delta P = P_0 - P_t\).

• Air flow velocity: \(v_a = \sqrt{\frac{2\Delta P}{\rho_a}}\).

3. Simple Carburetor

• Components: Float chamber (maintains fuel level), venturi, fuel jet, throttle valve.

• Working: Air flows through venturi → pressure drop at fuel jet → fuel sucked from float chamber.

• Float chamber venting: Ventilated to atmosphere to maintain atmospheric pressure in float chamber; otherwise, fuel flow would be affected by altitude changes.

4. Limitations of Simple Carburetor

• No compensation for engine speed/load.

• Poor mixture at part load.

• No altitude compensation.

• Backfire risk.

5. Carburetor Circuits

• Float circuit: Maintains fuel level.

• Idle circuit: Low throttle operation.

• Main circuit: Normal operation.

• Power circuit: Acceleration enrichment.

• Choke: Cold start enrichment.

6. Carburetor Calculations

• Air flow rate (compressible flow through venturi):

$$\dot{m}_a = C_d A_t P_0 \sqrt{\frac{2\gamma}{R(\gamma-1)}\left[\left(\frac{P_t}{P_0}\right)^{2/\gamma} - \left(\frac{P_t}{P_0}\right)^{(\gamma+1)/\gamma}\right]}$$

where \(P_t = P_0 - \Delta P\), \(C_d\) = discharge coefficient.

• Fuel flow rate:

$$\dot{m}_f = C_f A_f \sqrt{2\rho_f (P_t - P_{fuel} - \rho_f g h)}$$

\(h\) = fuel head (vertical distance from fuel surface to jet).

• Air-Fuel Ratio: \(A/F = \dot{m}_a / \dot{m}_f\).

• With nozzle lip considered: Effective pressure at fuel orifice reduced by dynamic pressure of air:

$$\dot{m}_f = C_f A_f \sqrt{2\rho_f (P_t - P_{fuel} - \rho_f g h - \frac{1}{2}\rho_a v_a^2)}$$

7. Mixture Types

• Rich: \(A/F < 14.7:1\) (gasoline), more fuel, cooler, incomplete combustion.

• Stoichiometric: \(A/F \approx 14.7:1\), ideal for catalytic converter.

• Lean: \(A/F > 14.7:1\), less fuel, hotter, better economy but risk of mis-fire.

B. Multi-Point Fuel Injection (MPFI)

• System: Injector per cylinder, located near intake valve; electronic control (ECU) based on sensors.

• Merits over carburetor:

  • Accurate metering per cylinder.

  • Better fuel economy & emissions.

  • No throttle losses (in some systems).

  • Better cold-start performance.

• Demerits: Higher cost, complexity, maintenance.

VI. FUELS AND ALTERNATIVE FUELS

A. Chemical Composition of Fuels

B. Fuel Ratings

1. Octane Number (SI Engines)

• Definition: Percentage by volume of iso-octane in mixture with n-heptane that matches knocking tendency of test fuel.

• RON (Research Octane Number): Mild test conditions.

• MON (Motor Octane Number): Severe test conditions (higher engine speed, temperature).

• Anti-knock Index (AKI): \((\text{RON} + \text{MON})/2\).

2. Cetane Number (CI Engines)

• Definition: Percentage by volume of cetane (hexadecane) in mixture with heptamethylnonane that matches ignition delay of test fuel.

• Higher cetane → shorter ignition delay → smoother combustion.

• Measured in standard CFR engine.

C. Desirable Fuel Characteristics

D. Alternative Fuels (Frequent)

1. Gaseous Fuels

• CNG (Compressed Natural Gas): Mainly methane, high octane (~120), clean, low CO₂, but low energy density, requires high-pressure cylinders.

• LPG (Liquefied Petroleum Gas): Propane/butane, high octane, clean, stored as liquid under pressure.

• Biogas: Methane from biomass, similar to CNG but may contain CO₂, H₂S.

2. Hydrogen

• Properties: Wide flammability limits (4–75%), high flame speed, low density, high auto-ignition temperature.

• Usage in SI: Can be used with modifications (higher compression, hardened valves).

• Usage in CI: Dual-fuel (pilot diesel ignition), or hydrogen-diesel co-combustion.

3. Biofuels

• Ethanol: From biomass, high octane, oxygenated, reduces CO, but hydrophilic, lower energy density, corrosion.

• Biodiesel: From vegetable oils/animal fats, similar to diesel, lower emissions (except NOx), can cause filter plugging.

4. Summary for SI and CI

E. Fuel Additives (Dopes)

1. Purpose:

• Improve combustion (octane/cetane boosters).

• Reduce emissions (detergents, smoke suppressants).

• Protect engine (corrosion inhibitors, antioxidants).

• Improve storage stability (anti-oxidants, metal deactivators).

2. Requirements of Good Additive:

• Effective at low concentration.

• Compatible with fuel and engine materials.

• Stable under storage and operating conditions.

• Non-corrosive, non-toxic.

3. Types:

• Antioxidants: Prevent gum formation (e.g., phenolic compounds).

• Anti-knock agents: Increase octane (e.g., tetraethyl lead [banned], MTBE, ETBE, aromatics).

• Detergents: Keep injectors/valves clean (e.g., polyisobutene amine).

• Cetane improvers: Alkyl nitrates (e.g., 2-ethylhexyl nitrate).

4. Knock Inhibitors:

• Lead-based (historical): Tetraethyl lead (TEL).

• Oxygenates: MTBE, ETBE, alcohols.

• Aromatics: Benzene, toluene (limited due to emissions).

VII. SUPERCHARGING AND TURBOCHARGING

A. Need for Supercharging

• Increase power output without increasing engine size.

• Improve torque at low speeds.

• Compensate for altitude loss (aircraft engines).

• Enhance acceleration.

B. Effect on Engine Performance

C. Methods of Supercharging

1. Positive Displacement Superchargers

• Roots: Two meshing lobes, positive displacement, boost at low rpm, inefficient at high speed.

• Vane: Rotor with sliding vanes, smoother but wear issues.

• Twin-screw: Two meshing screws, high efficiency, compact.

2. Dynamic Superchargers (Centrifugal)

• Impeller accelerates air, diffuser converts velocity to pressure.

• Boost increases with rpm (lag at low speed).

3. Turbocharging

• Need: Utilize exhaust gas energy, improve efficiency.

• Methods:

  • Constant pressure: All exhaust gases combined into single turbine (simple, but pulse energy lost).

  • Pulse turbocharging: Exhaust pulses from individual cylinders directed to turbine (utilizes pulse energy, more efficient).

• Merits: No parasitic loss (uses waste energy), high efficiency.

• Demerits: Turbo lag, high exhaust backpressure, heat, complexity.

D. Thermodynamic Cycle of Supercharged Engine

• Intake pressure > atmospheric → higher mass of air per cycle.

• Net work increases, but compression work may increase if supercharger is driven mechanically.

• For turbocharged, exhaust energy recovery improves overall efficiency.

E. Limitations of Supercharging

• SI Engines:

  • Knock limit: Maximum pressure/temperature before knock.

  • Mechanical limits: Piston, connecting rod strength.

• CI Engines:

  • Pressure limits: Fuel injection system must handle higher pressures.

  • Smoke limit: Air availability may become insufficient at high loads.

VIII. ENGINE COOLING SYSTEMS

A. Need for Cooling

• Prevent overheating and seizure.

• Maintain efficient operation (optimal temperature ~80–100°C).

• Reduce detonation tendency in SI engines.

• Ensure proper lubrication (oil viscosity).

B. Types of Cooling Systems

1. Air Cooling: Fins on cylinder/head, airflow from vehicle motion or fan. Simple, no coolant, but uneven cooling.

2. Liquid Cooling: Coolant (water/antifreeze) circulated through jackets, radiator dissipates heat.

3. Forced Cooling System (most common):

   DiagramSEARCH: engine forced liquid cooling system diagram

   • Components: Water pump, thermostat, radiator, fan, coolant passages.

   • Working: Pump circulates hot coolant to radiator → cooled by air → returns to engine. Thermostat regulates flow to maintain operating temperature.

C. Cooling System Components

• Radiator: Heat exchanger (tubes + fins).

• Cooling Fins: Increase surface area on air-cooled engines.

• Water Pump: Centrifugal type, driven by belt.

• Thermostat: Wax-pellet type, opens at ~80°C.

• Fan: Mechanical or electric, draws air through radiator.

D. Coolants

• Anti-freeze Solutions:

  • Ethylene glycol (toxic) or propylene glycol (less toxic).

  • Lower freezing point, raise boiling point, inhibit corrosion.

• Additives: Corrosion inhibitors (phosphates, silicates), anti-foaming agents.

• Selection & Maintenance:

  • Concentration 30–50% glycol in water.

  • Periodic flushing, check for leaks, test freeze point.

IX. ENGINE LUBRICATION SYSTEMS

A. Functions of Lubrication

• Reduce friction and wear.

• Seal piston rings against cylinder wall.

• Cool moving parts (carry heat away).

• Clean (carry contaminants to filter).

• Prevent corrosion.

B. Properties of Lubricating Oil

• Viscosity: Appropriate for temperature range (SAE grades).

• Pour point: Lowest temperature for flow.

• Flash point: Minimum temperature for ignition (safety).

• Carbon residue: Tendency to form deposits.

• Acidity: Low acid number to prevent corrosion.

• Demulsibility: Ability to separate from water.

C. Types of Lubrication Systems

1. Splash Lubrication: Moving parts (e.g., connecting rod) dip in oil and splash around. Used in small engines.

2. Pressure Feed (Forced):

   • Oil pump supplies pressurized oil to main bearings, camshaft, etc.

   • Full-flow filter filters all oil.

   • DiagramSEARCH: engine pressure lubrication system diagram

3. Mist Lubrication: Oil mixed with air, used in 2-stroke engines (oil injected into intake).

4. Dry Sump vs Wet Sump:

   • Wet sump: Oil stored in pan, pump picks up oil. Simple but oil sloshes.

   • Dry sump: External tank, scavenge pumps, no oil in sump. Better for high-performance, reduces foaming.

D. Lubrication System Sketch

X. EMISSIONS AND CONTROL SYSTEMS

A. Exhaust Gas Recirculation (EGR)

• Purpose: Reduce NOx emissions by lowering combustion temperature.

• Construction & Working:

  • Internal EGR: Exhaust gases routed back via valve in intake manifold.

  • External EGR: Separate cooler and valve, more control.

  • Working: Inert exhaust gases displace air → lower oxygen → lower peak temperature → less NOx.

• Advantages: Effective NOx reduction, relatively simple.

• Limitations: Increases soot (especially in CI), reduces efficiency, requires cooling to avoid intake heating, may cause drivability issues.

B. Scavenging in 2-Stroke Engines

• Need: Efficiently remove exhaust gases and fill cylinder with fresh charge (no separate intake stroke).

• Types:

  DiagramSEARCH: 2 stroke engine scavenging types cross loop uniflow

  • Cross scavenging: Transfer and exhaust ports on opposite sides, baffles direct flow. Simple but some short-circuiting.

  • Loop scavenging: Transfer ports angled, creates looped flow, better scavenging.

  • Uniflow scavenging: Exhaust valve at top, inlet at bottom, unidirectional flow (most efficient, used in large marine engines).

• Scavenging Efficiency: Ratio of fresh charge retained to total cylinder volume.

XI. ADVANCED ENGINE CONCEPTS AND MISCELLANEOUS

A. 2-Stroke vs 4-Stroke Engines

B. Wankel Engine

• Construction: Triangular rotor in epitrochoid chamber, no pistons.

• Working: Rotor's motion creates expanding/contracting volumes; intake, compression, power, exhaust in separate zones.

• Advantages: Compact, smooth (no reciprocating mass), high rpm, high power/weight.

• Disadvantages: Poor fuel economy (large surface/volume ratio, heat loss), high emissions, apex seal wear, poor low-speed torque.

• DiagramSEARCH: Wankel rotary engine diagram

C. Cylinder Arrangement

• In-line: All cylinders in a row. Simple, good for 4-6 cylinders.

• V-type: Two banks angled (e.g., 60°, 90°). Shorter, rigid, used in 6+ cylinders.

• Opposed (Flat): Horizontally opposed cylinders. Low center of gravity, smooth (e.g., Subaru, Porsche).

• Radial: Cylinders arranged radially around crankshaft. Used in aircraft (good cooling, smooth).

D. Microprocessor-Based Control Systems

• Advantages:

  • Precise control of fuel injection, ignition timing, emissions.

  • Adaptive to conditions (altitude, temperature).

  • Onboard diagnostics (OBD).

  • Improved fuel economy and performance.

• Disadvantages:

  • High cost and complexity.

  • Susceptible to electromagnetic interference.

  • Requires skilled maintenance.

  • Dependency on sensors (failure leads to poor performance).

\boxed{\eta_{Otto} = 1 - \frac{1}{r^{\gamma-1}}}

\boxed{\eta_{Diesel} = 1 - \frac{1}{r^{\gamma-1}} \left( \frac{\alpha^\gamma - 1}{\gamma(\alpha - 1)} \right)}

\boxed{IP_{Morse} = \frac{n \cdot BP_{all} - \sum BP_i}{n-1}}

\boxed{MEP = \frac{Work\ per\ cycle}{Swept\ volume}}