Automobile Engines and Electric Vehicles

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Real IC engines do not follow ideal air-standard cycles.

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This section explains the fuel-air cycle and its assumptions, the composition of cylinder gases, the actual cycle and its losses, and compares thermodynamic (air-standard), fuel-air and actual cycles.

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Air-Standard Cycle Assumptions (Recap) • Working fluid is air behaving as an ideal gas with constant specific heats (γ = 1.4); fixed mass in a closed cycle; combustion replaced by heat addition from an external source and exhaust by heat rejection; compression and expansion isentropic; no heat loss, friction or chemical change. • Gives the upper limit of efficiency (Otto: η = 1 − 1/rγ−1); useful for comparing effects of compression ratio, cut-off ratio etc.

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Fuel-Air Cycle and Assumptions in Fuel-Air Analysis • The fuel-air cycle is a closer approximation that accounts for the real working medium.

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Factors considered: • (1) Actual composition of cylinder gases — air, fuel vapour and residual gases before combustion; combustion products after. • (2) Variation of specific heats with temperature — cp and cv increase with temperature (γ decreases), so the peak temperature and pressure reached are lower and efficiency is lower. • (3) Dissociation at high temperature (above ≈ 1500 °C):

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CO2 ⇌ CO + ½O2, H2O ⇌ H2 + ½O2 — absorbs heat, lowering maximum temperature; partial re-association during expansion releases some heat late.

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Dissociation is greatest near the stoichiometric mixture. • (4) Change in number of molecules (molecular expansion/contraction) during combustion. • Assumptions in fuel-air analysis: no chemical change in fuel or air before combustion; after combustion the charge is in chemical equilibrium; compression and expansion are frictionless and adiabatic (isentropic); combustion is instantaneous at TDC (constant volume for SI); fuel is completely vaporised and perfectly mixed; no heat loss to walls; velocities negligible; residual gas fraction known. • Effect of mixture strength: fuel-air cycle efficiency increases as the mixture becomes leaner (lower temperatures, less dissociation, higher γ); maximum power and peak temperature occur with a slightly rich mixture (≈ 10–15% rich). • For the same compression ratio, fuel-air cycle efficiency is substantially lower than air-standard efficiency (e.g., r = 8: air-standard ≈ 56.5%, fuel-air ≈ 40–45%).

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Composition of Cylinder Gases • Before combustion: fresh charge — air + fuel vapour (SI) or air only (CI, fuel injected later) — plus residual gases (burned gases left in the clearance volume from the previous cycle) and any EGR. • Residual gas fraction: typically a few per cent at full load, rising to ≈ 15–20% at light load in throttled SI engines and with low compression ratio.

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Residuals dilute the charge, lower flame temperature and flame speed (less NOx, but slower burning and possible misfire). • After combustion: mainly N2 (≈ 70%+), CO2 and H2O; with lean mixtures excess O2; with rich mixtures CO and H2; plus dissociated species (CO, H2, OH, O, H, NO) at high temperature. • Mixture strength is expressed by air-fuel ratio, equivalence ratio φ = (F/A)actual/(F/A)stoich or λ = 1/φ; stoichiometric A/F for petrol ≈ 14.7, diesel ≈ 14.5.

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Actual Cycle and Its Losses • The actual (indicated) P-V diagram has rounded corners and lower peak pressure than the fuel-air cycle.

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Losses: • Time loss — combustion takes finite time (≈ 40–60° crank angle), so heat is not added at constant volume; spark must be advanced (optimum = MBT timing). • Heat loss to cylinder walls, piston and head during combustion and expansion (≈ 10–12% of fuel energy in the cycle). • Exhaust blow-down loss — exhaust valve opens before BDC, losing some expansion work (but reducing pumping work in the exhaust stroke). • Pumping loss — negative work during intake and exhaust strokes (large at part throttle in SI engines). • Rubbing friction, incomplete combustion, blow-by (gas leakage past rings) and crevice volumes. • Actual indicated efficiency ≈ 80–85% of the fuel-air cycle efficiency (for SI engines).

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Feature Air-standard cycle Fuel-air cycle Actual cycle Working medium Air only, ideal gas Air + fuel + residuals, real properties Real mixture, changing composition Specific heats Constant Vary with temperature Vary Dissociation Ignored Considered Present Combustion Heat addition (instantaneous) Instantaneous, adiabatic Finite time, with heat loss Losses None None (except property effects) Time, heat, blow-down, pumping, friction, leakage Efficiency Highest Lower Lowest Peak pressure/temperature Highest Lower Lowest, rounded diagram

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This section covers the classification of IC engines, nomenclature, the main parts with their functions, materials and manufacturing processes (casting and forging), and a comparison of four-stroke and two-stroke engines including performance aspects.

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Classification of IC Engines Basis Types Thermodynamic cycle Otto (constant volume), Diesel (constant pressure), dual/mixed, Atkinson/Miller Strokes per cycle Four-stroke, two-stroke Ignition Spark ignition (SI), compression ignition (CI) Fuel Petrol, diesel, CNG, LPG, alcohol, hydrogen, dual-fuel, bi-fuel, multi-fuel Fuel supply Carburetted, port fuel injection, direct injection (GDI, DI diesel), common rail Charging Naturally aspirated, supercharged, turbocharged Cooling Air-cooled, liquid (water)-cooled Cylinder arrangement In-line, V, flat (horizontally opposed/boxer), W, radial, opposed-piston Valve location L-head (side valve), I-head (overhead valve), F-head, T-head Combustion chamber (CI) Direct injection (open chamber), indirect injection (pre-chamber, swirl chamber) Speed / application Low, medium, high speed; automotive, marine, locomotive, stationary, aircraft Nomenclature • Bore D, stroke L (= 2 × crank radius), TDC, BDC, swept volume Vs = (π/4)D²L, clearance volume Vc, compression ratio r = (Vs + Vc)/Vc, engine displacement = Vs × number of cylinders (e.g., 1500 cc). • Mean piston speed Vp = 2LN/60 m/s (typically 8–15 m/s in cars; limited by inertia stresses and friction). • Stroke-to-bore ratio: square (L/D = 1); over-square / short-stroke (L/D < 1 — high-speed petrol engines, lower piston speed, room for bigger valves); under-square / long-stroke (L/D > 1 — diesel and torque-oriented engines). • Specific output (kW per litre), power-to-weight ratio, bmep, torque, bsfc are key performance measures.

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Engine Parts, Functions, Materials and Manufacture Part Function Material Manufacture Cylinder block Houses cylinders, water jackets, crankcase Grey cast iron; aluminium alloy with liners Sand casting; die casting / lost-foam (Al) Cylinder head Closes cylinder; combustion chamber, ports, valves Aluminium alloy (good conductivity) or CI Sand/permanent-mould casting Cylinder liner Replaceable wear surface; dry (no coolant contact) or wet (in contact with coolant) Alloy/Ni-hard cast iron Centrifugal casting, bored and honed Piston Transmits gas force; forms moving wall Al-Si alloy (light, good conductivity; low expansion);

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CI/steel in heavy diesels Gravity die casting; forging for high performance Piston rings Seal gas (compression rings), control oil (oil ring), transfer heat Fine-grain alloy cast iron; steel; chrome/moly coated Cast/turned, split Gudgeon pin Connects piston to small end Case-hardened alloy steel (hollow) Machined, ground Connecting rod Converts reciprocating to rotary motion Medium-carbon/alloy steel (I-section); powder-forged steel Drop forging Crankshaft Converts motion to torque; carries counterweights Forged Ni-Cr/Cr-Mo steel or SG (nodular) cast iron Drop forging or casting; journals induction-harden ed/nitrided, ground Camshaft Operates valves Chilled cast iron, SG iron, forged/assembled steel Casting/forging; lobes hardened Inlet valve / exhaust valve Control gas flow Inlet:

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Si-Cr martensitic steel.

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Exhaust: austenitic (21-4N) steel, Nimonic, sodium-filled hollow stem Upset forging, machined, faced with Stellite Flywheel Stores energy, smooths torque; carries ring gear and clutch face Cast iron or steel Casting, machining Crankcase / oil sump Encloses crank; stores oil Cast Al or pressed steel Casting / pressing Manifolds Distribute intake / collect exhaust Intake:

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Al or glass-filled nylon.

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CI, SG iron, stainless steel Casting / moulding / fabrication Engine bearings Support crankshaft and big ends Steel-backed babbitt, Al-Sn, Cu-Pb (tri-metal) Strip, rolled shells Cylinder-head gasket Seals head to block Multi-layer steel (MLS), composite Stamped • Casting is used for complex hollow shapes (blocks, heads, pistons, manifolds, liners); forging gives continuous grain flow and higher fatigue strength for highly stressed parts (connecting rods, crankshafts, valves, gears). • Casting processes in engine manufacture: sand casting (CI blocks and heads), gravity/pressure die casting (Al pistons, blocks), centrifugal casting (liners), lost-foam (some Al blocks/heads), investment casting (turbocharger turbine wheels).

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Four-Stroke vs Two-Stroke Engines Feature Four-stroke Two-stroke Power strokes 1 per 2 crank revolutions 1 per revolution (theoretically 2× power; actually ≈ 1.5–1.7×) Valves / ports Poppet valves and valve train Ports (inlet, transfer, exhaust); reed valves Scavenging Separate exhaust stroke — good Fresh charge pushes out exhaust — some charge lost (short-circuiting) Thermal efficiency / fuel economy Higher Lower Emissions Lower Higher HC (charge loss, oil burning) Lubrication Pressure feed from sump Petroil or separate oil injection (crankcase scavenged) Torque uniformity / flywheel Less uniform — heavier flywheel More uniform — lighter flywheel Weight, size, cost Heavier, more parts Lighter, simpler, cheaper Applications Cars, trucks, most motorcycles Mopeds, chainsaws, outboards, very large marine diesels • Two-stroke scavenging methods: cross-flow (deflector piston), loop / reverse flow (Schnurle), uniflow (exhaust valves in head or opposed pistons — most efficient; large marine diesels).

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Scavenging performance: delivery ratio, scavenging efficiency, trapping efficiency, charging efficiency.

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Most automobile engines have several cylinders.

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This section covers cyclic torque and the flywheel effect, merits and limitations of single- and multi-cylinder engines, arrangement of cylinders, firing order and engine balancing.

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Cyclic Torque and the Flywheel Effect • The turning moment (torque) diagram of an engine fluctuates over the cycle: large positive torque during the power stroke, small or negative torque during suction, compression and exhaust. • Single-cylinder four-stroke: one power impulse per 720° → very large fluctuation → needs a heavy flywheel. • Firing interval (even firing) = 720°/n for four-stroke and 360°/n for two-stroke engines (n = number of cylinders).

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120° (power strokes overlap → smoother);

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90°. • The flywheel stores energy during the power stroke and releases it during idle strokes; required size ∝ fluctuation of energy ΔE = Iω²Cs.

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More cylinders → smoother torque → lighter flywheel, better acceleration. • Torsional vibration dampers (harmonic balancers — rubber or viscous) on the crankshaft nose and dual-mass flywheels reduce torsional vibrations.

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Merits and Limitations of Single- and Multi-Cylinder Engines Aspect Single-cylinder Multi-cylinder Torque Very uneven — heavy flywheel Smooth, overlapping impulses — light flywheel Balance / vibration Poor — difficult to balance Good — forces and couples can cancel Power Limited (large single cylinder has high inertia forces, knock tendency, cooling problems) High power with small cylinders at high speed; better power-to-weight Acceleration and starting Poorer Better Cost, parts, maintenance Simple, cheap, easy to maintain More parts, more complex and costly Friction / size Low friction, compact More friction, larger Uses Motorcycles, small gensets, pumps, tillers Cars, buses, trucks, larger motorcycles Arrangement of Cylinders Arrangement Features Examples In-line (straight) Cylinders in one row; simple, easy maintenance; long for 6+ cylinders 3-, 4-cylinder cars; in-line 6 trucks V-type Two banks at 60° or 90° on a common crankshaft; compact, short and rigid V6, V8, V12 engines Flat / horizontally opposed (boxer) Two banks at 180°; low centre of gravity, good balance, wide Subaru, Porsche, VW Beetle W-type Three or four banks (or two narrow-V banks) VW W12, Bugatti W16 Radial Cylinders arranged radially around crankshaft Aircraft piston engines Opposed-piston Two pistons per cylinder, no cylinder head Some large diesels, military engines Firing Order • Firing order: the sequence in which the cylinders deliver their power strokes. • Considerations: even spacing of power impulses; engine balance and minimum vibration; avoid consecutive firing of adjacent cylinders (reduces crankshaft torsional stress and main-bearing loads and concentration of heat); even distribution of intake charge (avoid 'charge robbing'); uniform cooling; exhaust pulse separation. • Common firing orders:

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3-cylinder 1-2-3; in-line 4-cylinder 1-3-4-2 (or 1-2-4-3);

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5-cylinder 1-2-4-5-3; in-line 6-cylinder 1-5-3-6-2-4 (or 1-4-2-6-3-5);

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1-8-4-3-6-5-7-2 or 1-5-4-8-6-3-7-2 (manufacturer-specific). • Cylinder 1 is usually at the front (timing end).

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Ignition leads and injector wiring must follow the firing order.

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Engine Balancing • Rotating masses (crankpin, big end) are balanced completely by crankshaft counterweights. • Reciprocating masses produce primary forces (m ω²r cos θ — at crank frequency) and secondary forces (m ω²r cos 2θ/n — at twice crank frequency, n = l/r), plus primary and secondary couples in multi-cylinder engines. • Single-cylinder: primary and secondary forces unbalanced; primary partly balanced (≈ 50–75% of reciprocating mass) by counterweights — the rest transferred to a perpendicular direction. • In-line 4-cylinder (flat-plane crank, 180°): primary forces and couples balanced; secondary forces NOT balanced (they add up) → vibration at 2 × engine speed; larger engines use Lanchester balance shafts (two shafts rotating in opposite directions at twice crank speed). • In-line 6-cylinder: primary and secondary forces and couples all balanced — inherently balanced (very smooth). • In-line 3-cylinder: forces balanced but primary couple (rocking) unbalanced — often a balance shaft.

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Flat-4 (boxer): primary and secondary forces balanced; small couples.

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90° V8 (cross-plane): forces balanced; primary couple cancelled by crank counterweights. • Dynamic balancing of crankshaft, flywheel and clutch assembly and matched weights of pistons and connecting rods are done during manufacture/rebuild.

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Valves control the entry of fresh charge and exit of exhaust gases.

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This section covers arrangement of valves, design aspects of intake and exhaust manifolds, inlet and exhaust valves, valve springs, rocker arms, tappets and the valve train, and the valve timing diagram.

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Arrangement of Valves Head type Arrangement Remarks L-head (side valve) Both valves in the block beside the cylinder Simple, low height; poor breathing, low compression ratio — obsolete I-head (overhead valve) Both valves in the cylinder head above piston Compact chamber, good breathing, high CR — universal today F-head Inlet valve in head, exhaust in block Old designs T-head Inlet and exhaust valves on opposite sides in block Obsolete • Camshaft location: cam-in-block OHV (pushrod) — camshaft in block, pushrods and rockers;

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SOHC (single overhead camshaft);

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DOHC (double overhead camshaft — separate intake and exhaust camshafts; usually 4 valves per cylinder).

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OHC reduces reciprocating valve-train mass → higher permissible speed. • Multi-valve heads (3, 4 or 5 valves per cylinder): larger total valve flow area, better volumetric efficiency at high speed, central spark plug (short flame travel), smaller lighter valves. • Variable valve timing (VVT) — cam phasers change timing with speed/load (e.g., VVT-i); variable valve lift (e.g., Honda VTEC, BMW Valvetronic — throttle-less load control); cam-less electro-hydraulic/electromagnetic valves are under development.

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Design Aspects of Intake and Exhaust Manifolds • Intake manifold: equal-length runners and even distribution to all cylinders; smooth bends and adequate cross-section (low pressure loss); tuned runner length to use ram (inertia) and wave (Helmholtz resonance) effects — long runners boost low-speed torque, short runners high-speed power (variable-length intake manifolds); suitable plenum volume; heating ('hot spot') in carburetted engines for fuel vaporisation, cool intake in injected engines for higher density; light materials (Al, glass-filled nylon). • Exhaust manifold: low back pressure; tuned (pulse) lengths — e.g., 4-2-1 headers — so that exhaust pulses help scavenge cylinders and do not interfere with each other; withstand high temperature and thermal cycling (cast iron, SG iron, stainless steel); retain heat for quick catalyst light-off (close-coupled catalysts); integrate turbocharger in turbo engines.

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Inlet and Exhaust Valves • Poppet (mushroom) valves are universal: head, face (seat angle usually 45°, sometimes 30° for inlet), margin, stem, collet (keeper) groove, tip.

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Others: sleeve valves, rotary valves, reed valves (two-strokes). • Inlet valve is larger than the exhaust valve — incoming charge is driven only by a small pressure difference, and a larger area improves volumetric efficiency; exhaust gas leaves under higher pressure. • Exhaust valve runs hottest (≈ 700–800 °C): made of austenitic heat-resisting steel (21-4N), Nimonic alloys;

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Stellite-faced; sodium-filled hollow stem for cooling; valve rotators for even seat wear.

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Inlet valve: martensitic Si-Cr steel. • Valve seats: hardened inserts (alloy CI, Stellite) — needed for unleaded fuel; valve guides of cast iron or bronze. • Design: valve lift ≈ d/4 (curtain area πdL equals port area); port diameter from continuity: d ≈ D√(Vp/Vg) (Vp = mean piston speed, Vg = permissible gas velocity). • Valve problems: burning (poor seating, lean mixture, insufficient clearance), sticking (deposits), seat recession, spring breakage, valve float.

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Valve Springs, Rocker Arms, Tappets and Valve Train • Valve train (OHV): cam → tappet (follower) → pushrod → rocker arm → valve; valve spring closes the valve.

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OHC: cam acts on a bucket tappet or finger/roller rocker directly.

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Camshaft is driven by gears, chain or toothed belt at half crankshaft speed (four-stroke). • Valve springs: close-coiled helical compression springs (oil-tempered Cr-V/Cr-Si steel, shot-peened) that close the valve quickly and keep the follower on the cam.

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At high speed, insufficient spring force causes valve float/bounce; spring surge (resonance of coils) is prevented by double springs wound in opposite hands, variable-pitch or conical (beehive) springs.

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Alternatives: pneumatic springs (racing), desmodromic valves (mechanically closed). • Rocker arm: lever that transmits cam motion to the valve and reverses direction in OHV engines; rocker ratio (typically ≈ 1.5–1.7) multiplies cam lift; mounted on a rocker shaft or stud; roller-tipped rockers reduce friction. • Tappets (lifters / cam followers): mechanical (solid) tappets need a valve (tappet) clearance to allow thermal expansion — exhaust clearance larger than inlet because the exhaust valve gets hotter (typical cold values ≈ 0.15–0.25 mm inlet, 0.20–0.35 mm exhaust; follow manufacturer data).

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Hydraulic tappets self-adjust with engine oil pressure — zero lash, quiet, no adjustment.

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Roller tappets reduce friction; bucket tappets with shims in DOHC engines. • Clearance too small → valve may not seat → loss of compression and burnt valves; clearance too large → noisy 'tappet noise', reduced lift and duration, wear.

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Valve Timing Diagram • Valves do not open and close exactly at TDC and BDC; timing is chosen to improve breathing at operating speed: • Inlet valve opens before TDC (so it is fully open when suction starts) and closes after BDC (uses the inertia/ram effect of the moving charge to fill the cylinder). • Exhaust valve opens before BDC (blow-down lets pressure fall, reducing exhaust pumping work) and closes after TDC (exhaust gas inertia scavenges residuals). • Valve overlap: period near TDC when both valves are open (= IVO before TDC + EVC after TDC); larger in high-speed/performance engines, smaller in diesels (high CR, piston-valve clearance) and for smooth idling. • Spark timing ≈ 20–40° bTDC (advanced with speed); diesel injection ≈ 10–25° bTDC. • Two-stroke port timing diagram is symmetrical about BDC (exhaust port opens before transfer port and closes after it).

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Event (typical values) Four-stroke petrol engine Four-stroke diesel engine Inlet valve opens (IVO) 10–25° before TDC 10–15° before TDC Inlet valve closes (IVC) 25–60° after BDC 25–40° after BDC Exhaust valve opens (EVO) 40–55° before BDC 35–50° before BDC Exhaust valve closes (EVC) 10–20° after TDC 10–15° after TDC Valve overlap ≈ 20–45° ≈ 20–30°

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Electric vehicles (EVs) use electric motors powered by batteries (or fuel cells) for propulsion.

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This section introduces EV types including hybrids, the EV architecture, high-voltage and low-voltage systems and their components, AC and DC charging, and the main charging connector standards.

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Introduction • Advantages: zero tailpipe emissions, high efficiency (motor ≈ 90–95%; battery-to-wheel ≈ 80–90% vs ≈ 20–35% for IC engines), instant torque from zero speed, quiet and smooth, fewer moving parts and lower maintenance, regenerative braking, low running cost — particularly attractive in Nepal with hydro-electricity and lower import taxes on EVs. • Limitations: driving range and range anxiety, charging time, high battery cost and weight, battery degradation and end-of-life recycling, need for charging infrastructure, reduced range in cold weather and on steep hills. • Energy storage: lithium-ion batteries — NMC (nickel-manganese-cobalt; high energy density, cell ≈ 3.6–3.7 V), LFP (lithium iron phosphate; safer, longer cycle life, cheaper, cell ≈ 3.2 V, lower energy density), NCA; older NiMH (hybrids) and lead-acid (e-rickshaws).

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Cells → modules → pack.

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Types of Electric and Hybrid Vehicles Type Description Examples / remarks BEV (battery electric) Battery + motor only; charged from the grid (plug-in); no engine Most new EVs;

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Safa Tempo, e-buses, e-scooters HEV (hybrid electric) IC engine + motor + small battery charged by engine and regenerative braking;

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NOT plug-in Toyota Prius; micro (start-stop), mild (48 V assist), full hybrids PHEV (plug-in hybrid) Larger battery chargeable from grid; tens of km in pure electric mode, then hybrid Commuting on electricity, long trips on fuel EREV / REEV (range-extended) Electric drive only; small engine drives a generator to recharge battery Series-hybrid principle FCEV (fuel-cell electric) Hydrogen fuel cell generates electricity; small buffer battery Toyota Mirai, Hyundai Nexo • Hybrid architectures: series hybrid — engine drives a generator only; the motor alone drives the wheels (efficient in stop-go city driving); parallel hybrid — engine and motor can both drive the wheels mechanically (efficient on highways); series-parallel / power-split hybrid — a planetary gear set splits engine power between wheels and generator (e.g., Toyota Hybrid System) — combines both advantages. • Mild hybrids cannot drive on electricity alone; full hybrids can at low speed.

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Electric Vehicle Architecture (Block Diagram) • Charging port → on-board charger (OBC) (AC → DC for battery during AC charging) → high-voltage battery pack with battery management system (BMS) → power distribution unit / HV junction box (contactors, fuses, pre-charge circuit) → traction inverter (DC → variable-frequency 3-phase AC;

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IGBT or SiC MOSFET switches) → traction motor → single-speed reduction gear and differential → wheels. • DC-DC converter steps HV down to 12 V to charge the auxiliary battery and supply LV loads (replaces the alternator).

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Vehicle control unit (VCU) coordinates driver inputs, motor torque, regeneration and charging.

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Thermal management system cools/heats battery, motor and inverter (liquid cooling, heat pump). • Traction motors:

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PMSM (permanent-magnet synchronous — most common; high efficiency and power density), induction motor (no rare-earth magnets, rugged), BLDC (two- and three-wheelers), switched reluctance. • Regenerative braking: the motor acts as a generator during deceleration; the inverter returns energy to the battery.

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High-Voltage System and Components • High voltage in EVs means > 60 V DC or > 30 V AC (voltage class B); typical traction systems are ≈ 300–400 V, with newer 800 V platforms for faster charging. • Components: traction battery pack, BMS, traction inverter, traction motor, on-board charger, DC-DC converter, HV junction box/PDU with main contactors and pre-charge resistor (limits inrush current into inverter capacitors), fuses, orange-coloured HV cables, electric A/C compressor, PTC heater or heat pump, manual service disconnect, insulation monitoring device, high-voltage interlock loop (HVIL). • BMS functions: monitor cell voltages, temperatures and current; estimate state of charge (SOC) and state of health (SOH); cell balancing (passive/active); protect against over-charge, over-discharge, over-current, short circuit and over-temperature; control contactors and charging; communicate over CAN. • Safety: only trained technicians work on HV systems; use insulated tools and gloves; remove service disconnect and wait for capacitors to discharge; verify zero voltage before work.

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Low-Voltage System and Components • A 12 V (sometimes 48 V) auxiliary battery (lead-acid or lithium) powers the VCU and ECUs, lighting, wipers, power windows, infotainment, airbags and safety systems, and the contactor coils that connect the HV battery — a flat 12 V battery can prevent an EV from starting. • It is charged by the DC-DC converter from the HV battery (no alternator).

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Communication among ECUs uses CAN bus; body control module, instrument cluster, sensors and switches are on the LV network.

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Electric Vehicle Charging System Charging Power / time (approx.) Features AC slow charging (Level 1, household socket, 230 V) ≈ 2–3.3 kW;

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8–20+ h Portable charger (Mode 2) with in-cable protection AC Level 2 (wall box / public AC station) 7.4 kW single-phase;

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11–22 kW three-phase; ≈ 4–8 h Vehicle's on-board charger converts AC to DC — its rating limits power DC fast charging (Level 3) 25–50 kW (fast);

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150–350 kW (ultra-fast);

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20–80% in ≈ 20–60 min Off-board charger converts AC to DC and feeds battery directly, bypassing the OBC • Charging modes (IEC 61851):

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Mode 1 — ordinary socket without protection (not recommended);

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Mode 2 — household socket with in-cable control and protection device;

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Mode 3 — dedicated AC EVSE with control pilot;

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Mode 4 — DC fast charging. • Lithium-ion charging follows constant current (CC) then constant voltage (CV); power tapers above ≈ 80% SOC to protect cells.

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Slow charging is gentler on battery life; frequent fast charging raises battery temperature and ageing. • Other methods: battery swapping (common for two- and three-wheelers), wireless inductive charging, vehicle-to-grid (V2G) and vehicle-to-home (V2H) with bidirectional chargers.

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Types of Charging Connectors Connector Type Region / features Type 1 (SAE J1772) AC, single-phase;

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5 pins North America, Japan; up to ≈ 7.4 kW typical.

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CCS1 adds two DC pins for fast charging Type 2 (IEC 62196-2, 'Mennekes') AC, single- and three-phase;

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7 pins Europe standard; up to 22 kW (43 kW); widely used in India/Nepal.

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CCS2 (Combo 2) = Type 2 + two DC pins for fast charging up to ≈ 350 kW CHAdeMO DC fast charging only; separate large connector Japanese standard (Nissan Leaf, Mitsubishi);

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CAN communication; supports bidirectional V2G/V2H; ≈ 50 kW common, higher in later versions GB/T (GB/T 20234) Separate AC and DC connectors Chinese national standard; used by Chinese-made EVs (many in Nepal);

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DC up to ≈ 250 A NACS (SAE J3400) Combined AC/DC compact connector Tesla standard, adopted widely in North America

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This section covers advanced engine concepts: low heat rejection (adiabatic) engines, homogeneous charge compression ignition (HCCI), the rotary (Wankel) engine, the six-stroke engine concept and recent developments in IC engines.

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Low Heat Rejection (LHR) Engines • Also called adiabatic or insulated engines: combustion-chamber surfaces (piston crown, cylinder head, liner, valves) are coated with ceramic thermal barrier coatings — partially/yttria-stabilised zirconia (PSZ/YSZ), silicon nitride, alumina — to reduce heat loss to the coolant. • Aims/advantages: more of the fuel energy retained for work and in the exhaust (for turbo-compounding), higher thermal efficiency, smaller or no cooling system (lighter, fewer parts), shorter ignition delay (hot walls) → less diesel knock, multi-fuel capability, lower HC, CO and smoke. • Problems: higher NOx (higher temperature), lower volumetric efficiency (hot intake air), lubricating-oil breakdown at high liner temperature, thermal shock and spalling of coatings, tribological problems, knock tendency in SI engines.

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Degrees: partially, moderately and fully insulated.

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Homogeneous Charge Compression Ignition (HCCI) • A premixed, homogeneous, lean (or highly diluted) fuel-air mixture (as in SI engines) is auto-ignited by compression (as in CI engines) — no spark and no injection-controlled diffusion flame; combustion occurs almost simultaneously throughout the charge (volumetric combustion). • Advantages: diesel-like high efficiency (high compression ratio, unthrottled, lean), very low NOx (low combustion temperature) and very low soot/PM (no rich zones), fuel flexibility. • Challenges: controlling the ignition timing (no direct trigger — depends on temperature, pressure, composition and EGR); narrow operating range — misfire at low load, excessive pressure-rise rate/knock at high load; high HC and CO emissions; cold starting. • Control methods: variable valve timing (trapping hot residuals / internal EGR), external EGR, intake-air heating, variable compression ratio, dual fuels.

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PCCI, RCCI (reactivity-controlled, dual-fuel), GCI, and SPCCI — spark-controlled compression ignition used in Mazda's Skyactiv-X.

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Rotary (Wankel) Engine • Invented by Felix Wankel (first run 1957, NSU); used in Mazda RX-7 and RX-8 and as a range extender.

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A triangular (Reuleaux-shaped) rotor turns eccentrically inside an epitrochoidal housing, forming three working chambers. • Each rotor face goes through intake, compression, power and exhaust in one rotor revolution; the eccentric (output) shaft turns three times per rotor revolution → one power impulse per output-shaft revolution for each rotor.

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Gas exchange through ports — no valves, camshaft or connecting rods. • Advantages: compact and light (high power-to-weight), few moving parts, no reciprocating masses — smooth and fully balanced, high rpm capability. • Disadvantages: apex-seal wear and leakage, elongated combustion chamber with high surface-to-volume ratio (heat loss, unburnt HC), higher fuel and oil consumption, higher emissions, poor low-speed torque.

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Six-Stroke Engine Concept • Adds two extra strokes to the four-stroke cycle, mainly to recover waste heat and improve efficiency. • Crower six-stroke (Bruce Crower, 2006): after the normal exhaust stroke, water is injected into the hot cylinder; it flashes into steam and drives a second power (steam) stroke, followed by a steam exhaust stroke — recovers heat, cools the engine internally (smaller cooling system) and improves fuel economy. • Other concepts:

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Bajulaz six-stroke (separate air preheating chamber), Velozeta six-stroke (fresh air injected for the extra strokes — cooling and scavenging), Beare Head (opposed-piston head). • Status: experimental — advantages of higher efficiency and lower emissions are offset by complexity, extra water tank and freezing/corrosion problems.

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Recent Developments in IC Engines Development Purpose / example Downsizing with turbocharging Small 3- or 4-cylinder turbo engines (e.g., 1.0 L) with high specific output and better economy Gasoline direct injection (GDI) Precise fuelling, charge cooling, higher compression ratio, stratified lean operation Common-rail diesel with piezo injectors Multiple injections (pilot, main, post), very high pressures, low noise and emissions Variable valve timing and lift VVT-i, VTEC, Valvetronic — better torque curve, throttle-less load control Cylinder deactivation Shut down some cylinders at light load to reduce pumping loss Variable compression ratio Multi-link mechanism (e.g., Nissan VC-Turbo) to optimise efficiency and power Atkinson/Miller cycle High-expansion cycle in hybrids for efficiency Start-stop and 48 V mild hybrids Stop engine at idle; electric assist and regeneration Advanced turbocharging Variable-geometry, twin-scroll, electric-assisted (e-turbo) turbochargers Emission control Cooled EGR, SCR with urea, DPF and gasoline particulate filters (GPF), close-coupled catalysts;

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Euro 6/7, BS-VI norms Advanced combustion HCCI/SPCCI, lean burn, pre-chamber (turbulent-jet) ignition, water injection Alternative fuels CNG, LPG, ethanol flex-fuel, biodiesel, hydrogen IC engines, synthetic e-fuels Friction and thermal management Low-friction coatings (DLC), low-viscosity oils, split cooling, electric water/oil pumps; camless valve trains (e.g., Freevalve)