Engine Testing, Performance and Batteries

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This section defines the parameters used to judge engine performance and explains how brake power, indicated power, friction power, fuel and air consumption and BMEP are measured on a test bed, followed by the performance characteristics of SI and CI engines.

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Basic Performance Parameters Parameter Definition / formula Brake power (BP) Useful power at the crankshaft:

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BP = 2πNT/60000 kW (N in rpm, T in N·m) Indicated power (IP) Power developed by gas on the piston:

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IP = pmi·L·A·n·k/60000 kW (pmi in Pa); n = N/2 for 4-stroke, N for 2-stroke; k = number of cylinders Friction power (FP) FP = IP − BP (friction + pumping + auxiliaries) Mechanical efficiency ηm = BP/IP (≈ 75–90% at full load) Mean effective pressure IMEP from indicator diagram (area/length × spring constant);

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BMEP = ηm × IMEP = BP×60000/(L·A·n·k) Brake specific fuel consumption bsfc = ṁf/BP (kg/kWh) — petrol ≈ 0.25–0.35, diesel ≈ 0.20–0.25 kg/kWh at best point Thermal efficiencies ηith = IP/(ṁf·CV); ηbth = BP/(ṁf·CV) = ηm·ηith = 3600/(bsfc·CV) with bsfc in kg/kWh, CV in kJ/kg Volumetric efficiency ηv = actual mass (or volume at ambient) of air inducted ÷ mass of air that would fill swept volume at ambient conditions Specific output / power BP per unit piston area or displacement (kW/L); power-to-weight ratio Measurement of Brake Power — Dynamometers • Absorption dynamometers (power absorbed and dissipated as heat):

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Prony brake (friction blocks on a brake drum, BP = 2πN·W·L/60000); rope brake (BP = (W − S)·π(D + d)·N/60000, W = dead load, S = spring-balance reading, D = drum dia, d = rope dia); hydraulic (water) dynamometer (fluid friction between rotor and stator — high power, used for big engines); eddy-current dynamometer (rotor cuts magnetic field; eddy currents produce braking torque — easily controlled, compact, widely used). • Transmission dynamometers: measure torque being transmitted without absorbing it — torsion dynamometer (shaft twist, strain gauges), belt transmission dynamometer. • Driving dynamometers: electric swinging-field (cradle) DC/AC dynamometer — can absorb power and also drive (motor) the engine, hence used for motoring tests of friction power. • Chassis dynamometer (rolling road): vehicle drives on rollers — used for emission testing (drive cycles) and road-load simulation. • Torque is measured by a load cell/spring balance on a torque arm (T = F × arm length); speed by tachometer or magnetic pickup.

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Measurement of Indicated Power • Indicator diagram (p–V) obtained by a mechanical piston indicator (low-speed engines) or, in modern practice, a piezoelectric pressure transducer with a crank-angle encoder (p–θ converted to p–V) and data acquisition. • IMEP = (area of indicator diagram × spring constant)/length of diagram; then IP = pmiLAnk/60000. • Alternatively IP = BP + FP, with FP found by the methods below.

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Measurement of Friction Power Method Principle Remarks Willans line (fuel-rate extrapolation) Plot fuel consumption vs BP at constant speed; extrapolate the straight line to zero fuel — the negative intercept on BP axis = FP Only for CI engines (fuel line nearly straight at low load); not for throttled SI engines Morse test Multi-cylinder engine at constant speed; cut off each cylinder in turn (spark shorted / injector cut) and restore speed by reducing load.

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IP of cut cylinder = BPtotal − BPwith that cylinder cut; ΣIP − BP = FP Only for multi-cylinder engines; assumes pumping/friction unchanged Motoring test Engine run at test speed by an electric (swinging-field) dynamometer with fuel/spark off; power required ≈ FP Over-estimates slightly (cold, lower gas loads) — common in labs Retardation test Engine cut off at a speed; time to decelerate at no load and at known load compared Needs moment of inertia; approximate From indicator diagram FP = IP (from p–V) − BP (dynamometer) Accuracy depends on IP measurement Fuel and Air Consumption • Fuel consumption: volumetric — time to consume a known volume (e.g., 10 or 50 cc) from a burette, ṁf = V·ρf/t; gravimetric — mass consumed from a vessel on a balance in a timed period (independent of temperature/density); flowmeters (Coriolis, positive-displacement) for continuous measurement. • Air consumption: air-box method — engine draws air from a large box (volume ≥ 500 × swept volume) through a sharp-edged orifice; the box damps pulsations; pressure drop measured by a U-tube manometer:

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V̇ = CdA√(2ghwρw/ρa).

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Viscous-flow (Alcock) meter — laminar flow, Δp ∝ flow; hot-wire/hot-film anemometers and MAF sensors. • Air-fuel ratio = ṁa/ṁf; also found from exhaust-gas analysis (CO2, O2, CO).

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Performance Characteristics of SI and CI Engines • Variable-speed test at full throttle/rack: torque (and BMEP) rises to a maximum at medium speed (best volumetric efficiency), then falls;

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BP increases with speed up to a maximum at a higher speed than the maximum-torque speed, then falls (friction and falling ηv); bsfc is lowest near medium speed. • Load control:

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SI engines use quantity governing (throttle reduces mixture quantity;

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A/F nearly constant) → pumping loss at part load, bsfc rises sharply at light load.

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CI engines use quality governing (air unthrottled; fuel quantity varied, A/F varies from ≈ 18 :

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1 at full load to 80+ :

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1 at idle) → better part-load economy. • Diesel torque curve is flatter and peaks at lower speed; diesel bsfc is ≈ 20–30% lower; petrol engines have higher specific power (higher speeds, lighter). • Variable-load test at constant speed: bsfc falls as load increases (ηm improves), minimum near 75–90% load, then may rise slightly (rich mixture in SI / smoke limit in CI).

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Factors Affecting Performance of SI Engines Factor Effect Compression ratio Higher CR → higher efficiency and power, limited by knock Air-fuel ratio Slightly rich (≈ 12.5–13) for max power; lean (≈ 16) for economy Spark timing MBT timing (minimum advance for best torque) gives max power; over-advance → knock; retard → loss, hot exhaust Volumetric efficiency Governed by valve timing, manifold tuning, intake temperature, speed; affects power directly Engine speed Higher speed → more power up to a limit, more friction, lower ηv Combustion chamber & turbulence Compact chamber, central plug and swirl/squish → faster burning, less knock Atmospheric conditions High altitude / hot air → lower density → less power (≈ 1% per 100 m altitude for NA engines) Mechanical condition Worn rings/valves, fouled plugs, clogged air filter reduce power

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This section explains how mechanical, indicated thermal, brake thermal and volumetric efficiencies vary with engine load and speed for SI and CI engines, and how an engine heat balance sheet is drawn up from test data.

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Effect of Load (at Constant Speed) Efficiency SI engine CI engine Mechanical ηm Zero at no load; rises with load (FP ≈ constant at constant speed, plus pumping loss falls as throttle opens) Zero at no load; rises with load — maximum at full load Indicated thermal ηith Nearly constant over most of the load range (A/F nearly constant); falls a little at light load (residual dilution, rich idle) and at full load (enrichment) Increases as load decreases (leaner overall mixture, closer to air-standard); highest at light load Brake thermal ηbth Rises with load, maximum near full load; very low at light load (throttling + friction) Rises with load to a maximum at ≈ 75–80% load, then falls slightly (smoky, less complete combustion) Volumetric ηv Falls sharply at part load (throttle restricts air) Almost independent of load (no throttle); slight fall at high load due to hotter walls Effect of Speed (at Full Throttle / Full Load) • Mechanical efficiency falls with increasing speed — friction power rises roughly with speed² (piston, bearing, pumping and auxiliary losses). • Indicated thermal efficiency is roughly constant over the middle speed range; lower at very low speed (more heat loss per cycle, poorer turbulence) and slightly lower at high speed in CI engines (less time for combustion). • Brake thermal efficiency is maximum at a medium speed and falls at high speed because ηm falls. • Volumetric efficiency is maximum at a medium speed (where valve timing and intake/exhaust tuning suit); falls at low speed (back-flow at late IVC) and at high speed (flow friction, choking at valves, less time, charge heating). • Since torque ∝ ηv × ηbth approximately, the torque curve follows the volumetric-efficiency curve — max torque at medium speed.

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Heat Balance Sheet The heat balance sheet accounts for the energy supplied by the fuel (per minute or per hour) and shows how it is distributed.

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It is drawn from a test at a fixed load and speed.

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Item How determined Heat supplied by fuel Qs = ṁf × CV (lower calorific value) (a) Heat equivalent of BP BP (kJ/s) from dynamometer (b) Heat to cooling water Qw = ṁw cpw (Tout − Tin) (c) Heat carried by exhaust gases Qg = ṁg cpg (Tg − Tatm), ṁg = ṁa + ṁf; or measured with an exhaust-gas calorimeter (water-cooled heat exchanger) (d) Unaccounted losses Qs − (a + b + c): radiation, friction heat not in coolant, incomplete combustion, heat in lubricating oil, etc.

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Heat distribution (full load, typical) Petrol (SI) Diesel (CI) Brake power (useful work) ≈ 21–28% ≈ 29–42% Cooling water ≈ 12–27% ≈ 15–35% Heat distribution (full load, typical) Petrol (SI) Diesel (CI) Exhaust gases ≈ 30–55% ≈ 25–45% Unaccounted (radiation, etc.) ≈ 0–15% ≈ 5–15% • Heat balance can also be drawn against load: as load rises, BP percentage rises, coolant percentage falls. • Recovering exhaust heat: turbocharging, exhaust-gas heat recovery (turbo-compounding, thermoelectric), cabin heating from coolant.

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This section covers alcohols, hydrogen, natural gas, LPG, biodiesel, biogas and producer gas: their properties and suitability for SI and CI engines, alternative-fuel vehicles with examples, and their merits and demerits.

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Why Alternative Fuels? • Depletion and price of petroleum; energy security (Nepal imports all petroleum products from India); urban air pollution (CO, HC, NOx, PM) and CO2 emissions; use of local renewable resources (biomass, hydro-electricity for EVs and green hydrogen). • A good alternative fuel should be available in quantity, cheap, safe, of high energy density, compatible with engine materials and with existing fuel infrastructure, and cleaner burning.

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Properties Compared Fuel LHV (MJ/kg) Stoich.

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A/F Octane / cetane Key feature Petrol ≈ 44 14.7 RON 91–98 Reference SI fuel Diesel ≈ 42.5 14.5 CN 45–55 Reference CI fuel Ethanol C2H5OH ≈ 27 ≈ 9.0 RON ≈ 108 High latent heat, oxygenated, renewable Methanol CH3OH ≈ 20 ≈ 6.4 RON ≈ 109 Toxic, corrosive, invisible flame CNG (≈ 90%+ CH4) ≈ 47–50 ≈ 17.2 RON ≈ 120–130 Stored at ≈ 200–250 bar; lighter than air LPG (propane + butane) ≈ 46 ≈ 15.5 RON ≈ 105–110 Stored liquid at ≈ 5–10 bar; heavier than air Hydrogen H2 ≈ 120 ≈ 34 RON > 130 Flammability 4–75%; very low ignition energy Biodiesel (FAME) ≈ 37–38 ≈ 12.5 CN ≈ 50–65 ≈ 11% oxygen, biodegradable Biogas (≈ 55–65% CH4 + CO2) ≈ 20 MJ/m³ ≈ 6–10 High (CO2 suppresses knock) From anaerobic digestion Producer gas (CO, H2, N2) ≈ 4–6 MJ/m³ ≈ 1.1–1.3 High From gasification of wood/charcoal Alcohols (Ethanol and Methanol) • Produced from sugarcane/molasses, maize, cellulose (ethanol) or natural gas/coal/biomass (methanol). • Suitability: good SI fuels — high octane allows higher CR; high latent heat cools charge (higher ηv); oxygen content lowers CO and HC.

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Used as blends (E10, E20), flex-fuel (E85) or neat (E100 in Brazil).

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Poor CI fuels (very low cetane) — need ignition improvers or dual-fuel operation. • Demerits: lower calorific value (≈ 60% for ethanol) → higher volumetric fuel consumption; poor cold starting (high latent heat, single boiling point); corrosive to some metals and swells rubber/plastics; absorbs water (phase separation in blends); aldehyde emissions; methanol is toxic and burns with an almost invisible flame.

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Hydrogen • Produced by steam reforming of natural gas, coal gasification, or electrolysis of water (green hydrogen from hydro/solar power). • Merits: combustion product is water — no CO, HC, CO2 or smoke (only NOx in IC engines); highest energy per unit mass; wide flammability limits allow very lean operation; high flame speed; renewable.

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Can be used in IC engines or, more efficiently, in fuel-cell electric vehicles (FCEVs) such as Toyota Mirai and Hyundai Nexo. • Demerits: very low energy per unit volume — needs compressed storage at 350–700 bar, cryogenic liquid (−253 °C) or metal hydrides; low ignition energy → pre-ignition and backfire into the intake; high NOx near stoichiometric; embrittlement of metals; leakage and safety concerns; high cost and scarce infrastructure.

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Natural Gas (CNG/LNG) and LPG • CNG: mainly methane, stored at ≈ 200–250 bar in steel/composite cylinders.

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Very high octane (can use CR ≈ 12); clean burning — low CO, NMHC and PM, lower CO2 per km; no cold-start enrichment needed.

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Demerits: ≈ 10–15% power loss in converted petrol engines (gas displaces air, no charge cooling), bulky heavy cylinders, short range, refuelling infrastructure, methane is a greenhouse gas.

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Used in buses, taxis and three-wheelers (e.g., Delhi, Dhaka). • LPG (autogas): propane-butane mixture stored as liquid at ≈ 5–10 bar.

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High octane, clean, easy to carry; kits with vaporiser-regulator (converter) and mixer or gas injectors.

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Demerits: heavier than air — leaks collect in low places (fire hazard); some power loss; competition with domestic cooking use. • Dual-fuel / bi-fuel: bi-fuel vehicles run on petrol or gas; dual-fuel diesel engines run on gas ignited by a pilot diesel spray.

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Biodiesel, Biogas and Producer Gas • Biodiesel: fatty-acid methyl esters (FAME) made by transesterification of vegetable oils (jatropha, soybean, palm, rapeseed) or animal fats with methanol + catalyst (NaOH/KOH); by-product glycerol.

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Used neat (B100) or blended (B5, B20).

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Merits: renewable, higher cetane, good lubricity, sulphur-free, lower CO, HC, PM.

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Demerits: slightly lower CV and power, higher viscosity, poor cold-flow (gelling), slightly higher NOx, oxidation instability, may attack rubber seals.

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Straight vegetable oil causes injector coking due to high viscosity — transesterification solves this. • Biogas: from anaerobic digestion of cattle dung, kitchen and agricultural waste (well developed in Nepal for household cooking).

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Contains ≈ 55–65% CH4, 35–45% CO2, traces of H2S.

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For vehicles it is upgraded (scrubbed of CO2 and H2S) and compressed to bio-CNG.

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Used in SI engines or dual-fuel CI engines. • Producer gas: made by partial combustion (gasification) of wood, charcoal or agricultural residue with limited air — CO ≈ 20%, H2 ≈ 15–20%, N2 ≈ 50%, CO2, CH4.

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Very low CV; power loss ≈ 30–40%; tar and dust must be cleaned; used in stationary engines and historically in wartime vehicles.

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Alternative Fuel Vehicles Type Examples / notes Flex-fuel vehicles (FFV) Run on any petrol–ethanol blend up to E85/E100 using an alcohol sensor to adjust injection and timing (Brazil, USA) CNG / LPG vehicles Dedicated, bi-fuel or dual-fuel buses, taxis, auto-rickshaws Biodiesel vehicles Unmodified diesel engines on B5–B20;

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B100 needs seal and filter changes Hydrogen vehicles H2-ICE (BMW Hydrogen 7) and fuel-cell EVs (Toyota Mirai, Hyundai Nexo) Electric and hybrid vehicles Battery EVs, HEVs, PHEVs (see Chapter 5.6) — in Nepal, EVs charged from hydro-electricity reduce petroleum imports; the three-wheeled electric 'Safa tempo' has operated in Kathmandu since the 1990s

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This section describes the Electronic Control Module (ECM) — its structure, the inputs it needs and the outputs it drives — and the basics of the Controller Area Network (CAN) bus and its protocol used for communication between vehicle control units.

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Why Electronic Engine Control? • Mechanical systems (carburettor, distributor advance) cannot hold the A/F at λ = 1 accurately enough for a three-way catalyst, nor meet modern emission and fuel-economy norms. • Electronic control gives precise fuel metering and spark timing for every operating point, closed-loop feedback, adaptive learning, diagnostics (OBD) and integration with transmission, ABS and body systems.

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Electronic Control Module (ECM / ECU / PCM) Block Function Power supply / regulator Converts battery voltage (≈ 9–16 V) to stable 5 V reference for sensors and logic Input signal conditioning Filtering, amplification, protection;

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A/D converter for analog sensors; pulse shaping for frequency signals (CKP, speed) Microprocessor (CPU) Executes control programs — calculates injection pulse width, spark advance, idle speed, etc.

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Memory ROM/Flash — program and calibration look-up tables (maps);

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RAM — temporary data;

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KAM (keep-alive memory) — adaptive values and fault codes retained while battery connected;

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EEPROM — VIN, immobiliser data Output drivers Power transistors that switch actuators (low-side/high-side, PWM) — injectors, coils, relays, solenoids, motors Communication interface CAN transceiver, diagnostic (OBD) link Inputs and Outputs of the ECM Inputs (sensors / switches) Outputs (actuators) Crankshaft position & engine speed (CKP) Fuel injectors (pulse width and timing) Camshaft position (CMP) Ignition coils / igniter (dwell and spark advance) Mass air flow (MAF) or manifold pressure (MAP) Electronic throttle motor / idle air control valve Throttle position (TPS) and accelerator pedal position (APP) Fuel pump relay Coolant temperature (ECT), intake air temperature (IAT) EVAP canister purge solenoid Exhaust oxygen (O2/λ) sensors EGR valve, variable valve timing solenoids Knock sensor Radiator fan relay, A/C compressor clutch Vehicle speed, battery voltage, A/C request, gear position, brake switch Malfunction indicator lamp (MIL, 'check engine'); data to other ECUs over CAN Modes of Operation • Open loop:

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ECM uses stored maps only — during cold start and warm-up (O2 sensor not hot), wide-open throttle, and sensor faults. • Closed loop: once the engine and O2 sensor are warm, the ECM trims fuel continuously using O2 feedback to keep λ ≈ 1 (short-term and long-term fuel trims). • Limp-home (fail-safe) mode: substitute default values when a sensor fails so the vehicle can still be driven. • On-Board Diagnostics (OBD-II / EOBD): monitors sensors, misfire and catalyst efficiency; stores diagnostic trouble codes (DTCs) such as P0301 (cylinder 1 misfire) readable by a scan tool through the 16-pin OBD connector; turns on the MIL.

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Controller Area Network (CAN) Bus • Developed by Bosch (1986); standardised as ISO 11898.

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Replaces point-to-point wiring between ECUs (engine, transmission, ABS, airbag, body, instrument cluster) with a shared two-wire bus → less wiring, weight and cost; sensor data shared. • Physical layer: two wires, CAN-High and CAN-Low, twisted pair; differential signalling gives immunity to noise.

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Bus terminated by a 120 Ω resistor at each end (≈ 60 Ω measured across the bus). • Bit levels: recessive (logic 1) — both lines ≈ 2.5 V (difference ≈ 0 V); dominant (logic 0) — CAN-H ≈ 3.5 V, CAN-L ≈ 1.5 V (difference ≈ 2 V).

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A dominant bit overrides a recessive bit. • Speeds: high-speed CAN up to 1 Mbit/s (powertrain, typically 500 kbit/s); low-speed fault-tolerant CAN up to 125 kbit/s (body/comfort);

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CAN FD (flexible data rate) up to ≈ 5–8 Mbit/s with up to 64 data bytes. • Multi-master, message-based broadcast: nodes do not have addresses; each message has an identifier (11-bit standard CAN 2.0A or 29-bit extended CAN 2.0B) indicating content and priority; every node receives every message and filters those it needs. • Arbitration (CSMA/CR — non-destructive bitwise): if two nodes transmit together, each compares bus level with its own bit; a node sending recessive but reading dominant stops.

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The message with the lowest identifier value has the highest priority and continues without delay.

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CAN data frame field Content Start of Frame (SOF) One dominant bit — synchronises all nodes Arbitration field Identifier (11 or 29 bits) + RTR bit Control field IDE bit, reserved bit, DLC (data length code, 0–8 bytes) Data field 0–8 bytes (up to 64 in CAN FD) CRC field 15-bit cyclic redundancy check + delimiter ACK field Receivers overwrite the ACK slot with a dominant bit to acknowledge End of Frame (EOF) Seven recessive bits • Frame types: data frame, remote frame, error frame, overload frame.

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Error handling: bit, stuff, CRC, form and ACK errors; error counters move a faulty node to error-passive and then bus-off so it cannot block the network.

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Bit stuffing: after 5 identical bits a complementary bit is inserted. • Other vehicle networks:

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LIN (single wire, ≈ 20 kbit/s, master-slave — windows, mirrors, seats), FlexRay (10 Mbit/s, deterministic — chassis/x-by-wire), MOST (optical — infotainment), Automotive Ethernet (100 Mbit/s–1 Gbit/s — cameras, ADAS).

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This section covers the construction and role of the main engine-management sensors (throttle position, intake-air and coolant temperature, crankshaft and camshaft position, mass air flow and exhaust oxygen) and the output systems: electronic spark control, air management, idle speed control, electronic throttle control, fuel pump, purge control solenoid valve and injectors.

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Input Sensors Sensor Construction / principle Signal and importance to ECM Throttle position (TPS) Potentiometer (3 wires:

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5 V ref, signal, earth) on throttle shaft; newer: non-contact Hall type, dual track ≈ 0.5 V closed → ≈ 4.5 V wide open; load, acceleration enrichment, deceleration fuel cut-off, idle recognition, gear-shift in automatics Intake air temperature (IAT) NTC thermistor (resistance falls as temperature rises) in air cleaner/manifold or built into MAF Air density correction of fuel quantity; spark retard with hot air Engine coolant temperature (ECT) NTC thermistor in a brass probe in the coolant passage near the thermostat Cold-start enrichment, warm-up, idle speed, open/closed loop decision, fan control, spark timing — one of the most important sensors Crankshaft position (CKP) Inductive (magnetic) pickup — permanent magnet + coil facing a toothed reluctor (e.g., 60-2 teeth), AC voltage rising with speed; or Hall-effect sensor giving a digital square wave Engine speed and crank angle (TDC reference from missing tooth) — needed for injection and ignition timing; no CKP signal = no start Camshaft position (CMP) Usually Hall-effect (or inductive) sensing a lobe/trigger wheel on the camshaft Identifies cylinder 1 compression stroke (camshaft turns at half crank speed) → sequential injection, coil-on-plug firing, VVT feedback Mass air flow (MAF) Hot-wire or hot-film element heated above air temperature; current needed to keep it hot ∝ air mass flow (older: vane/flap meter, Karman vortex) Direct measure of air mass (density compensated) → basic fuel quantity (load); alternative is the MAP sensor (speed-density system) Exhaust gas oxygen (EGO / λ) sensor Zirconia (ZrO2) ceramic thimble with platinum electrodes — generates voltage from O2 difference between exhaust and outside air; works above ≈ 300–350 °C (heated HEGO); titania type changes resistance; wideband (UEGO/air-fuel ratio) sensor with pump cell ≈ 0.1 V lean, ≈ 0.9 V rich, switching at ≈ 0.45 V (λ = 1) → closed-loop fuel control; downstream sensor monitors catalyst efficiency • Other sensors:

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MAP (piezo-resistive silicon diaphragm), knock sensor (piezoelectric accelerometer on block), vehicle speed sensor, accelerator pedal position (APP) sensor, fuel rail pressure sensor, oil pressure switch.

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Output Systems and Actuators System Construction / working and importance Electronic spark control (ESC) ECM computes spark advance from speed and load maps with corrections for ECT, IAT and knock; knock sensor feedback retards timing of the knocking cylinder and then advances it gradually — allows running close to the knock limit; ignition module/coil drivers control dwell Air management system Secondary air injection: an air pump (electric or belt-driven) and valves inject fresh air into exhaust ports during cold start to oxidise HC and CO and heat the catalyst quickly; later diverted to the catalyst or atmosphere.

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(Air management also covers intake air control — MAF/throttle/IAC) Idle speed control (ISC) Idle air control (IAC) valve — stepper motor or rotary solenoid that meters air bypassing the closed throttle;

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ECM raises idle for cold engine, A/C load, power steering, electrical load; in ETC systems the throttle motor itself controls idle Electronic throttle control (ETC, drive-by-wire) No cable: accelerator pedal position sensor (dual redundant) → ECM → DC motor opens throttle plate; dual TPS feedback; return springs hold a default 'limp-home' opening; enables cruise control, traction control, torque management and smoother emissions Electric fuel pump In-tank roller-cell or turbine (regenerative) pump driven by a DC motor, with check and relief valves; controlled via fuel pump relay — ECM primes it ≈ 2 s at key-on and runs it only when a CKP (rpm) signal exists (safety after crash); pressure ≈ 3–4 bar for port injection (regulator or returnless PWM control) Purge control solenoid valve (EVAP) Fuel vapour from the tank is stored in an activated-charcoal canister; when the engine is warm and in closed loop, the ECM opens the purge solenoid (PWM) so manifold vacuum draws vapour into the intake to be burned — prevents HC emission; a vent valve is used for leak testing Fuel injectors Solenoid valve: coil, armature, return spring, needle/ball/disc valve, filter screen, O-rings;

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ECM grounds the circuit — fuel quantity ∝ pulse width (≈ 1.5–20 ms) at constant pressure difference; high-impedance (≈ 12–16 Ω, saturated drive) or low-impedance (≈ 2–4 Ω, peak-and-hold drive); piezo injectors for GDI/diesel common rail

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This section covers the types of storage battery, the principle of operation and construction of the lead-acid battery, measurement of state of charge, capacity and efficiency ratings, factors affecting battery life, and battery maintenance.

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Functions and Types • Functions of the automotive battery: supply heavy current to the starter motor and ignition during cranking; supply electrical loads when the engine is off or when demand exceeds alternator output; stabilise system voltage (acts as a buffer/capacitor absorbing voltage spikes). • Primary cells are not rechargeable (dry cells); secondary (storage) cells are rechargeable — electrical energy stored as chemical energy.

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Type Nominal cell voltage Features / use Lead-acid (flooded, conventional) 2.0 V (≈ 2.1 V OCV) Cheapest, high cranking current; vent caps for topping up — SLI (starting, lighting, ignition) batteries Low-maintenance / maintenance-free (MF) 2.0 V Lead-calcium grids reduce gassing and water loss; sealed top, built-in hydrometer (eye) VRLA — AGM (absorbed glass mat) and gel 2.0 V Electrolyte immobilised; valve-regulated, recombines gases; start-stop vehicles, spill-proof Nickel-cadmium (Ni-Cd) 1.2 V Robust, long life, good at low temperature; expensive, toxic cadmium; memory effect Nickel-metal hydride (NiMH) 1.2 V Earlier hybrids (Toyota Prius); higher energy density than Ni-Cd Lithium-ion (NMC, NCA, LFP) ≈ 3.2–3.7 V Highest energy density — EV traction batteries (see Chapter 5.6); needs BMS Principle of Operation of the Lead-Acid Cell • Active materials: positive plate — lead peroxide (PbO2), dark chocolate-brown; negative plate — spongy lead (Pb), grey; electrolyte — dilute sulphuric acid (H2SO4 + water). • Overall reaction:

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Pb + PbO2 + 2H2SO4 ⇌ 2PbSO4 + 2H2O (discharge → ; charge ←). • On discharge: both plates change to lead sulphate, acid is consumed and water formed → specific gravity falls.

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PbSO4 is reconverted to PbO2 and Pb, acid is regenerated → SG rises; near full charge, water is electrolysed → hydrogen and oxygen gassing (explosive hydrogen). • Cell EMF ≈ 2.1 V regardless of plate size;

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12 V battery = 6 cells in series (24 V systems in trucks use two 12 V batteries in series).

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Plate area and number of plates decide capacity and current.

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Construction of Lead-Acid Battery Part Description Container (case) Hard rubber or polypropylene, divided into 6 cell compartments; ribs at bottom form sediment space for shed material (older designs) Grids Lead alloy frames holding active paste: lead-antimony (strong, but more gassing) or lead-calcium (low gassing — maintenance-free) Plates and plate groups Positive and negative plates interleaved; each cell has one more negative plate than positive (both outer plates negative) Separators Porous insulating sheets (microporous polyethylene envelopes, glass mat) between plates — prevent short circuit, allow electrolyte flow Cell connectors and terminals Lead straps connect cells in series; positive terminal post is larger than negative (marked + / red) Cover and vent plugs Vent caps allow gases out and permit topping up; flame arrestors in MF batteries Electrolyte H2SO4 diluted to SG ≈ 1.260–1.280 (fully charged, at 25–27 °C) Measuring State of Charge State of charge Specific gravity Open-circuit voltage (12 V battery) 100% ≈ 1.265–1.280 ≈ 12.6–12.7 V 75% ≈ 1.225 ≈ 12.4 V 50% ≈ 1.190 ≈ 12.2 V 25% ≈ 1.155 ≈ 12.0 V Discharged ≈ 1.110–1.120 ≈ 11.8 V or less • Hydrometer test: measures SG of each cell (correct ≈ 0.004 per 5.5 °C, or 0.0007 per °C, from reference); cells should not differ by more than ≈ 0.050 — a large difference indicates a faulty cell.

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Refractometers and the built-in 'magic eye' (green = charged) in MF batteries are alternatives. • Open-circuit voltage test: after removing surface charge; simple for sealed batteries. • High-rate discharge (load) test: apply a load of about ½ CCA (or ≈ 3 × Ah rating) for 15 s; voltage should stay above ≈ 9.6 V at 21 °C — checks ability to crank. • Cadmium probe test (individual plate potentials) and modern electronic conductance testers which estimate cranking ability without heavy loading.

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Capacity, Ratings and Efficiency • Ampere-hour capacity (C20): current a fully charged battery can supply for 20 hours at 27 °C (25 °C) until cell voltage falls to 1.75 V (10.5 V for 12 V).

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E.g., a 60 Ah battery gives 3 A for 20 h. • Reserve capacity (RC): minutes a battery can supply 25 A at 27 °C before voltage falls to 10.5 V — indicates how long the vehicle can run on battery if the charging system fails. • Cold cranking amperes (CCA): current a battery can deliver at −18 °C (0 °F) for 30 s while keeping voltage ≥ 7.2 V (1.2 V/cell) — cranking ability. • Capacity decreases with higher discharge rate (Peukert effect — less time for acid to diffuse into plates) and with low temperature (≈ 1% per °C below 27 °C; slower reactions, thicker electrolyte).

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It increases with plate area, number of plates and electrolyte quantity. • Ampere-hour efficiency = Ah output on discharge ÷ Ah input on charge ≈ 85–90%.

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Watt-hour (energy) efficiency = Wh output ÷ Wh input ≈ 70–80% (lower because charging voltage is higher than discharge voltage).

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Charging Methods • Constant-current charging (bench charging): current ≈ 10% of Ah capacity (e.g., 6 A for 60 Ah) until SG and voltage stop rising for 2–3 hours. • Constant-voltage (constant-potential) charging: used in vehicles — alternator with regulator holds ≈ 13.8–14.4 V; current tapers automatically as the battery charges. • Trickle charging (small current to keep stored batteries charged) and boost / fast charging (high current for short time — only to partially charge; avoid overheating above ≈ 45–50 °C).

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Battery Life, Failures and Maintenance Cause of failure Explanation Sulphation Battery left discharged forms hard, coarse PbSO4 crystals that do not reconvert → loss of capacity; most common cause Overcharging Excess gassing and water loss, heat, positive-grid corrosion, shedding of active material Undercharging / deep cycling Sulphation, stratification of acid;

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SLI batteries are not meant for deep discharge Vibration / loose mounting Active material shed, plates and connectors crack Freezing A discharged battery (SG ≈ 1.1) freezes at ≈ −8 °C; fully charged one only at ≈ −60 °C Low electrolyte Exposed plates dry and sulphate; high acid concentration • Typical life of an SLI lead-acid battery ≈ 3–5 years — reduced by heat, deep discharge, and short-trip use. • Maintenance: keep electrolyte ≈ 10–15 mm above plates by adding distilled water only (never acid unless spilled); keep top clean and dry (leakage current); clean corroded terminals with baking-soda solution and coat with petroleum jelly; keep clamps and hold-down tight; check SG/voltage and charging-system voltage regularly; do not leave discharged; store charged in a cool place. • Safety: hydrogen is explosive — no sparks or flames; disconnect the negative (earth) terminal first and reconnect it last; wear goggles and gloves (acid burns); when diluting, pour acid into water, never water into acid; jump-start positive to positive and the final negative connection to engine earth away from the battery.