Compendium

Internal Combustion Engines (Otto, Diesel, Modern) — Engineering Reference

28 min read

Internal Combustion Engines (Otto, Diesel, Modern) — Engineering Reference

1. At a glance

An internal combustion engine (ICE) converts the chemical energy of a fuel-air mixture into mechanical shaft work by burning the mixture inside a cylinder (or rotary chamber) whose volume is varied by a moving piston (or rotor). The expanding combustion gases push the piston; a connecting rod and crankshaft turn that reciprocating motion into rotation. This is distinguished from external combustion engines (Rankine steam, Stirling) where the working fluid is heated through a wall.

ICEs split on how combustion is initiated:

  • Spark-ignition (SI, Otto cycle, gasoline) — premixed homogeneous fuel-air charge is compressed and ignited by an electric spark at top dead centre (TDC). Compression ratio limited by knock; typically r = 9–12 for naturally aspirated, 8.5–10.5 for turbo. Otto 1876 patent.
  • Compression-ignition (CI, Diesel cycle, diesel oil) — air alone is compressed to high pressure and temperature (r = 14–22), and fuel is injected directly into the hot air near TDC. Ignition delay is short (~1 ms), then mixing-controlled combustion. Diesel 1893 patent.
  • Modern hybrids of the two: GDI (gasoline direct injection), TGDI (turbocharged GDI), HCCI (homogeneous-charge compression ignition), SPCCI (spark-controlled compression ignition, Mazda SkyActiv-X), dual-fuel diesel + natural gas, H₂-ICE.

In 2026, ICEs still power roughly 95 % of the world’s powered vehicles by parc, and every major automotive OEM ships at least one hybrid (HEV, PHEV, or 48 V mild). Marine (cargo, fishing, naval auxiliary), heavy-duty trucking, off-highway (construction, ag, mining), small non-road (lawn, marine outboard, motorcycle), rail (locomotive prime mover), and stand-by/peaking power are dominantly ICE — and likely will be through 2030 and well beyond for the heavy and marine categories.

Where ICE sits in the design stack: it consumes thermodynamics (Otto/Diesel/Atkinson/Miller cycles, dissociation, real-gas combustion), fluid-mechanics (port flow, swirl, tumble, compressible exhaust, turbocharger matching), heat-transfer (piston cooling, head temperature, charge heating, intercooler), chemical-process-fundamentals (combustion kinetics, NOₓ formation Zeldovich, soot formation), materials-ceramics (cast iron, aluminium alloys, Ni-superalloy turbo wheels, ceramic-coated pistons). It feeds classical-control (lambda, knock, idle-speed, boost-pressure control), system-identification (engine mapping), microcontrollers (ECU), and realtime-embedded (crank-angle-resolved interrupts).

2. Why it matters

Three facts keep the ICE dominant and worth engineering, even as battery-electric eats passenger volume:

  1. Energy density of liquid hydrocarbons is unmatched. Gasoline = 44.4 MJ/kg, diesel = 45.5 MJ/kg, kerosene = 43 MJ/kg. Compare Li-ion at battery-pack level: 0.65–0.85 MJ/kg (180–240 Wh/kg). Per-mass, fuel beats batteries by ~55×; per-volume, by ~10×. For long-haul trucking, ocean shipping, agriculture, aviation, military, and remote off-grid, that gap is not closable on a 2030 horizon.

  2. Regulatory tightening is constant but not lethal. Euro 7 (effective 1 Jul 2027 light-duty, 2029 HDV) keeps the Euro 6d NOₓ limit (60 mg/km gasoline, 80 mg/km diesel) but adds brake/tyre PM, on-board emissions monitoring (OBM) for the whole useful-life, and a 10 °C colder test floor (−10 °C cold-start). EPA HD Phase 3 (2027 MY) cuts heavy-duty on-highway NOₓ from 0.20 to 0.035 g/bhp-hr (–82 %) and tightens GHG. The engineering response is hot SCR + heated cat (electric pre-cat), close-coupled dual SCR, gasoline particulate filter (GPF), and aggressive thermal-management strategies.

  3. Decarbonisation does not require killing the ICE. Three drop-in vectors keep liquid-fuel infrastructure useful: (a) biofuels — HVO renewable diesel (NExBTL, neste) drop-in to existing diesel engines, sugarcane/cellulosic ethanol blends, FAME biodiesel up to B20. (b) e-fuels (synthetic hydrocarbons from green H₂ + captured CO₂) — Porsche/HIF Haru Oni pilot, Chile, 2022; net-CO₂-neutral if upstream electricity is renewable. (c) H₂-ICE — Toyota Corolla H2 (Super Taikyu race series 2021–2024), Cummins X15H (announced 2023, production 2025), JCB Hydrogen engine. Combustion is essentially zero-CO₂; NOₓ remains and must be controlled like a lean diesel.

The ICE engineer in 2026 is therefore working on (a) shrinking and turbo-charging gasoline engines, (b) bolting them to electric motors (48 V mild, P0/P1/P2/P3/P4 architectures, full HEV), and (c) keeping diesel viable under Euro 7 / EPA HD Phase 3 by cleaning up cold-start NOₓ and PN.

3. First principles

3.1 Idealised cycles

For air-standard (cold-air, γ = 1.4, c_v const) analysis, three cycles bound the practical engine:

Otto cycle (constant-volume heat addition) — SI engine idealisation.

η_Otto  =  1  −  1 / r^(γ − 1)

where r is the geometric compression ratio (V_BDC / V_TDC). For r = 10, γ = 1.4: η_Otto = 1 − 1/10^0.4 = 0.602. Real engines hit 0.30–0.37 because of heat transfer to walls, finite combustion duration, friction, and pumping work.

Diesel cycle (constant-pressure heat addition) — CI engine idealisation.

η_Diesel  =  1  −  (1 / r^(γ − 1)) · [(r_c^γ − 1) / (γ · (r_c − 1))]

where r_c = V_3 / V_2 is the cut-off ratio (cylinder volume at end of combustion / volume at start). At equal compression ratio Otto > Diesel, but Diesel runs at much higher r (14–22 vs. 9–12) and so wins overall.

Dual / Sabathe cycle — heat addition partly at constant V (Otto-like) then partly at constant P (Diesel-like). The real engine, especially modern common-rail diesel and HCCI, is closest to Dual.

Atkinson / Miller cycles — the intake valve closes late (Miller, after BDC) or early (Atkinson, before BDC), so the effective compression ratio is smaller than the geometric expansion ratio. The expansion stroke extracts more work from the same combustion event. Cost: lower volumetric efficiency, lower power density. Used in Toyota Prius (Atkinson, since 1997), Mazda SkyActiv-G (Miller, 14:1 geometric, 11:1 effective), Ford 1.5 L EcoBoost Atkinson mode, and most modern HEV gasoline engines because the hybrid motor covers the torque hole at low rpm.

3.2 Mean effective pressure

Brake mean effective pressure (BMEP) is the constant pressure that, if it acted on the piston during the entire power stroke, would produce the same brake (shaft) work the engine actually produces. It normalises torque for displacement and is the cleanest cross-engine comparison:

BMEP  =  (P_b · n_R · 60) / (V_d · N)        [Pa]

with P_b = brake power (W), n_R = revolutions per power stroke (2 for 4-stroke, 1 for 2-stroke), V_d = displacement (m³), N = engine speed (rev/s when consistent, or rev/min if 60 dropped). Typical values:

Engine classBMEP (bar)
NA gasoline, port-injected10–12
NA gasoline, GDI + DOHC + VVT12–14
Turbo GDI passenger, peak22–28
Top racing turbo (F1 1.6 V6t)~38
NA light-duty diesel8–10
Modern light-duty CR diesel turbo22–28
HD on-road diesel (Cummins X15, Volvo D13)28–32
Large 2-stroke marine (MAN B&W S60ME-C)17–21 (long-stroke trade)

3.3 Specific fuel consumption

Brake specific fuel consumption (BSFC) is fuel mass per unit brake work — the inverse of thermal efficiency scaled by fuel heating value:

BSFC  =  ṁ_f / P_b                  [g/(kW·h)  or  lb/(hp·h)]
η_b   =  3600 / (BSFC[g/kWh] · LHV[MJ/kg])

For gasoline LHV ≈ 43.4 MJ/kg, BSFC = 200 g/kWh → η = 0.415 (a peak-island number, only seen at one operating point). Typical numbers:

EnginePeak BSFC (g/kWh)Peak η_b
Modern gasoline NA, port-injected240–2600.32–0.35
Modern GDI Atkinson (Toyota A25A, Prius)218 (claimed 41 %)0.41
Modern turbo GDI Miller (Mazda SkyActiv-X)2190.41
Light-duty CR diesel (modern Euro 6d, VW EA288 evo)195–2050.40–0.42
HD diesel on-road (Cummins X15 Efficiency 2024)175–1850.46–0.48
Large marine 2-stroke (MAN B&W 6S60ME-C, HFO)165–1700.50–0.52

3.4 Mean piston speed and design speed limits

Mean piston speed:

S_p  =  2 · L · N                   [m/s]    (L = stroke in m, N in rev/s)

Practical ceilings, set by inertia stresses in the rod/piston assembly and ring-pack durability:

  • Passenger car gasoline: 14–17 m/s at redline
  • Performance / motorcycle gasoline: 20–24 m/s (e.g. Honda CBR1000RR: ~23 m/s)
  • F1 V6 turbo (15 000 rpm capped): ~18 m/s (stroke is short)
  • Heavy-duty diesel: 11–13 m/s
  • Large marine 2-stroke (very long stroke): 8–9 m/s at ~100 rpm rated

3.5 Air-fuel ratio, λ, equivalence ratio

For gasoline, stoichiometric AFR (mass) ≈ 14.7:1. For diesel, ≈ 14.5:1.

λ  =  AFR_actual / AFR_stoich        (>1 lean, <1 rich)
φ  =  1 / λ                          (>1 rich, <1 lean — combustion textbook)
  • SI three-way catalyst window: 0.99 ≤ λ ≤ 1.01 (extremely tight; managed by upstream universal exhaust gas oxygen (UEGO) sensor and downstream switching sensor)
  • Diesel: λ = 1.3 (full load, smoke-limited) to 6+ (idle)
  • Lean-burn GDI / stratified (early 2000s VW FSI, BMW HPI): λ up to 3 in stratified mode — NOₓ control problem killed it in Europe; LNT or SCR required.

4. Configuration space

AxisOptions
Cylinders1, 2, 3, 4, 5, 6, 8, 10, 12, 16
Cycle4-stroke (dominant), 2-stroke (large marine, lawn/handheld, outboard until ~2010)
ArrangementInline (I3, I4, I6), V (V6, V8, V10, V12), Boxer/flat (Subaru flat-4, Porsche flat-6), W (Bugatti, VW), Rotary/Wankel (Mazda RX-7/RX-8, Mazda MX-30 R-EV range extender 2023)
ValvetrainSide-valve (historical), OHV pushrod (US V8, e.g. GM LS, Chrysler Hemi), SOHC, DOHC, VVT (cam-phasing), VVL (cam-lobe switching, Honda VTEC, BMW Valvetronic, Fiat MultiAir hydraulic)
InductionNaturally aspirated, turbocharged (single, twin, sequential, twin-scroll, VGT), supercharged (Roots, twin-screw, centrifugal), electric supercharger (Audi SQ7 e-charger), turbo+super (Volvo T6 Polestar)
Fuel systemCarburettor (pre-1995 mass market; still small engines + classics), PFI port injection (~3–5 bar), GDI direct injection (~200 bar gasoline), common-rail diesel (1500–2700 bar)
CoolingWater/glycol (98 % of road), forced air (Porsche 911 to 1998, motorcycles, lawn), oil-cooled (some bike/race), hybrid (BMW R 1250 GS partial-water)
IgnitionSpark (coil-on-plug, magneto for small engines), compression, dual-fuel pilot

5. Spark-ignition details

Port fuel injection (PFI) — injectors spray into intake port upstream of intake valve. Fuel vaporises in the port. Clean combustion (no fuel-rich pockets), very low particulate matter (PM), good cold-start. Lower peak BMEP than GDI (no charge-cooling). Standard on most NA passenger gasoline through ~2010, still used on entry-level engines (Toyota 2GR-FE) and dual-injection systems (Toyota D-4S — both PFI and GDI on each cylinder, since 2005 Lexus IS350).

Gasoline direct injection (GDI) — injectors deliver fuel into combustion chamber at 100–350 bar. Cooling effect of in-cylinder vaporisation raises the knock-limited compression ratio by 1–1.5; permits higher BMEP and Miller-style late-intake-close strategies. Penalty: soot formation from locally rich pockets, leading to high particle number (PN) emissions. Gasoline Particulate Filter (GPF) is required on Euro 6d (1 Sep 2018+) and Euro 7 light-duty GDIs. Coupled passively to TWC; regenerates by passive oxidation under lean conditions.

Turbocharged GDI (“TGDI” or “downsizing”) — a 2.0 L T-GDI replaces a 3.5 L V6 NA, lowering pumping loss at part-load and shifting operating points toward the BSFC island. Industry workhorse 2010–2025: GM Ecotec LTG/LTH 2.0 T (Cadillac CTS, Camaro), Ford 2.3 EcoBoost (Mustang, Focus RS), VW EA888 evo4 2.0 TSI, BMW B48 2.0 T, Mercedes M254 2.0 T, Hyundai Theta II/Smartstream G2.5 T-GDi. Penalty: low-speed pre-ignition (LSPI), turbo lag, transient PN.

Atkinson / Miller GDI — modern HEV gasoline. Toyota’s M20A-FXS (Camry HEV 2018) and A25A-FXS (RAV4 HEV) — 2.5 L, 14:1, peak η ≈ 41 %. Mazda SkyActiv-G 2.0/2.5 — 14:1 geometric, peak η ≈ 40 %. Mazda SkyActiv-X — SPCCI, 16:1, ~43 % claimed peak BTE.

Homogeneous-Charge Compression Ignition (HCCI) — premixed lean charge that auto-ignites everywhere simultaneously when compressed. Very high efficiency, very low NOₓ (low temp), but narrow operating window (load, speed). Solo HCCI never made production passenger. SPCCI (spark-controlled CCI) — Mazda 2019 — uses a small spark-initiated stratified flame near the plug to trigger compression ignition of the surrounding lean charge. Production-validated.

Knock and LSPI — knock is end-gas auto-ignition before the flame front arrives; mitigated by retarding spark, cooled EGR, water/methanol injection (BMW M4 GTS 2016), higher-octane fuel. LSPI (Low-Speed Pre-Ignition) is a separate failure mode in turbo-GDI: oil/fuel droplets in the chamber auto-ignite a cycle or two before scheduled spark, producing huge cylinder pressures that can crack pistons or rods. Mitigation: low-Ca/Mg oil additives (API SP / ILSAC GF-6, dexos1 Gen 3), updated ECU pre-ignition detection (filtered ion-current or knock-sensor energy).

6. Compression-ignition (Diesel) details

Common-rail direct injection (CRDi) — high-pressure (1500–2700 bar) fuel rail feeds solenoid- or piezo-actuated injectors mounted in the head. Rail pressure decoupled from engine speed, so injection timing and pressure are independent variables. Per-cycle injection schedule typically has 5–9 events: 1–2 pilot pulses (quiet combustion, lower noise + NOₓ), main (bulk fuel), 1–3 post (raises exhaust T for SCR light-off, GPF regen). Industry leaders: Bosch, Denso, Delphi/Phinia, Continental Vitesco. Piezo injectors: 100 µs minimum pulse, 5+ pulses/cycle at 4000 rpm.

Variable Geometry Turbocharger (VGT) — pivoting nozzle vanes upstream of turbine wheel vary effective A/R. Matched boost across the rpm range; eliminates classical turbo lag. Honeywell GTB/GTD series (Garrett), BorgWarner. Critical for Euro 6d/HD2027.

Cooled EGR — recirculated exhaust (low-pressure or high-pressure routing) into the intake lowers peak combustion temperature, attacking Zeldovich (thermal) NOₓ formation directly. Cooled by glycol HX; rates up to 25–40 % on light-duty diesel, 30 % on HD. Trade: PM increases.

Diesel Oxidation Catalyst (DOC) — Pt/Pd on alumina/ceria washcoat on cordierite or metallic honeycomb. Oxidises CO, HC, and NO → NO₂ (the NO₂ is fuel for the downstream SCR). Light-off ~180 °C.

Diesel Particulate Filter (DPF) — cordierite (passenger) or SiC (HD, higher T capability) wall-flow monolith with alternate channels plugged. Gas forced through porous walls; soot deposits on wall surface. Filtration efficiency >99 % by mass, >95 % by number. Regenerated by raising exhaust T to ~600 °C via post-injection (active regen, every 500–1000 km on light-duty) or passively above 250 °C via NO₂-soot oxidation in CRT systems. Ash (engine-oil-derived Ca, Zn, P, S) accumulates non-regenerably — service-replace at ~200 000 km on passenger, ~500 000 km on HD (or longer with low-SAPS oils).

Selective Catalytic Reduction (SCR) — 32.5 % aqueous urea (AdBlue/DEF) injected upstream of a Cu- or Fe-zeolite (Chabazite, SAPO-34, SSZ-13) catalyst. Urea decomposes thermally to NH₃ + isocyanic acid → NH₃; ammonia + NOₓ → N₂ + H₂O. Conversion efficiency >90 % when SCR bed is >200 °C. Modern light-duty Euro 6d/Euro 7 architecture: close-coupled SCR-on-DPF (SCRF or SDPF) + underfloor SCR + ammonia slip catalyst (ASC). HD Phase 3 (US, 2027): often two SCRs, the first electrically pre-heated for cold-start.

Lean NOₓ Trap (LNT, NSC) — Ba/K NOₓ-storage component on Pt that adsorbs NOₓ during lean operation and releases/reduces it during periodic rich pulses. Used on small light-duty diesels lacking room for SCR (early VW MQB 1.6 TDI, BMW B47 N47). Sulfur-poisons. Mostly superseded by SCR.

Cetane Number — diesel ignition-quality metric, EN 590 minimum 51 in EU, ASTM D975 No. 2-D minimum 40 US. Higher CN → shorter ignition delay → quieter, lower NOₓ, easier cold-start.

Notable production diesels:

  • Light-duty: VW EA288 evo (2.0 TDI, Euro 6d), BMW B47 (2.0 TDI), Mercedes OM654 (2.0 CDI, twin-stage turbo, peak η ≈ 0.43), Mazda SkyActiv-D 2.2 (14:1 compression — uniquely low for a diesel, runs leaner combustion, lower NOₓ).
  • Heavy-duty on-road: Cummins X15 (15.0 L I6, peak ~605 hp, 2050 lb-ft, peak η ≈ 0.48 in X15 Efficiency), Volvo D13TC (13.0 L I6 with turbo-compounding), Detroit DD15 (14.8 L I6, Daimler), Paccar MX-13, Scania DC16 V8 (16.4 L, 770 hp).
  • Large 2-stroke marine: MAN Energy Solutions B&W S/G-ME-C/GI (uniflow-scavenged, electronically controlled exhaust valve and injectors). Example 6S60ME-C8.5: bore 600 mm, stroke 2400 mm, 6 cyl, 16 220 kW @ 105 rpm, BSFC 167 g/kWh, BTE ≈ 0.52 on HFO. Wärtsilä-Sulzer RT-flex similar class. Most are dual-fuel HFO/MDO/LNG (with diesel-cycle pilot ignition on LNG); methane-slip is the new regulatory target (IMO TIER III + EU CII).

7. Worked examples

7.1 Example A — Otto cycle gasoline engine, ideal + real BMEP

A 2.0 L inline-four, naturally aspirated, port-injected gasoline engine at 6000 rpm. r = 10, γ = 1.4.

Ideal Otto thermal efficiency:

η_Otto  =  1 − 1 / r^(γ − 1)
        =  1 − 1 / 10^0.4
        =  1 − 0.398
        =  0.602    (60.2 %)

Real engine at the same operating point: η_b ≈ 0.32 (well below ideal, due to heat loss to walls, incomplete and finite-duration combustion, friction, pumping work, exhaust blowdown loss).

Brake power at BMEP = 12 bar:

P_b  =  BMEP · V_d · N / (n_R · 60)
     =  12 × 10⁵ Pa · 2.0 × 10⁻³ m³ · 6000 rpm / (2 · 60)
     =  1.2 × 10⁶ · 2 × 10⁻³ · 50
     =  120 000 W  =  120 kW   (wait — check n_R)

Re-doing with 4-stroke n_R = 2: P_b = (P_me · V_d · N) / (2 · 60) for N in rev/min, P_me in Pa, V_d in m³:

P_b  =  (12 × 10⁵ · 2 × 10⁻³ · 6000) / (2 · 60)
     =  120 000 W  =  120 kW    [actually 60 kW is correct when BMEP is in bar and a 0.5 used for 4-stroke; let's recompute crisply]

Crisp formula for 4-stroke in mixed units:

P [kW]  =  BMEP [bar] · V_d [L] · N [rpm] / 1200
        =  12 · 2.0 · 6000 / 1200
        =  120 kW

That is a strong NA 2.0 L (≈ 60 hp/L). A practical road-going NA 2.0 L is typically 110–140 kW peak; 120 kW is plausible.

Fuel consumption at peak-η operating point (BSFC = 240 g/kWh):

ṁ_f  =  BSFC · P_b  =  240 g/kWh · 120 kW  =  28.8 kg/h

Volumetric (gasoline ρ ≈ 0.745 kg/L): 28.8 / 0.745 ≈ 38.7 L/h at full power.

7.2 Example B — Diesel common-rail injection schedule

Light-duty CR diesel, 2.0 L I4, rated 140 kW. Bosch CP4.2 pump, piezo injectors with 7-hole 130 µm nozzle.

Per-cycle fuel mass at full load, 4000 rpm:

ṁ_f      ≈  BSFC · P_b  =  200 g/kWh · 140 kW  =  28 000 g/h  =  7.78 g/s
cycles/s  =  N / (n_R · 60)  =  4000 / 120  =  33.3 /s/cyl  →  133.3 cycles/s for 4 cyl
m_f /cycle/cyl  =  7.78 / 133.3  ≈  0.0584 g  =  58.4 mg

A real full-load main pulse delivers ~50–60 mg; idle delivers ~1 mg. Rail pressure at full load: ~1800–2000 bar. Injection duration for 58 mg through a 130 µm 7-hole nozzle at 1800 bar: ~1.2 ms (≈ 29° crank @ 4000 rpm).

Spray cone: half-angle ~12°, full penetration 30–50 mm before wall impingement. Sauter mean diameter (SMD) at 1800 bar: ~6–9 µm — fine enough for fast evaporation in the ~30 µm hot-air boundary near TDC.

Pulse schedule example (full-load):

  1. Pilot 1 — 1.0 mg @ −18° aTDC
  2. Pilot 2 — 1.2 mg @ −8° aTDC
  3. Main — 50 mg @ −2° aTDC, 1.0 ms duration
  4. Post 1 (close-coupled) — 4 mg @ +12° aTDC, for soot oxidation in cylinder
  5. Post 2 (far) — 3 mg @ +60° aTDC, for DOC/DPF thermal management

Peak cylinder pressure: ~180–200 bar (lower than F1 turbo, but at sustained crank torque). EGR rate: 15–25 % cooled high-pressure EGR.

7.3 Example C — Modern hybrid 1.5 L T-GDI Miller, with 48 V mild hybrid

A 1.5 L inline-3 turbocharged GDI Miller-cycle engine, paired with a P0 belt-starter-generator (BSG) on a 48 V DC bus driving a small Class-C SUV (e.g. analogous to Ford 1.5 EcoBoost / Hyundai Smartstream G1.5 T-GDI + MHEV).

  • Geometric compression ratio: 12.0
  • Effective compression ratio (late IVC, Miller): ~9.5
  • Peak BMEP: 22 bar at 1500–3500 rpm (turbocharged); peak torque 250 N·m
  • Peak power: ~120 kW at 5500 rpm
  • Peak BTE at the BSFC island: 0.41, BSFC = 196 g/kWh
  • 48 V BSG: 10 kW continuous boost / regen, 50 N·m at the crank pulley

Cycle-average performance over WLTP for a 1450 kg Class-C SUV:

  • Engine-on fraction: ~78 % of cycle time (the BSG cannot move the vehicle alone)
  • Average engine load: 18 % of rated power
  • Average engine η: ~0.30 (well below peak; BSG-assisted load-shift recovers some)
  • Tank-to-wheels fuel economy: 5.0 L/100 km mixed (WLTP combined), 110 g CO₂/km
  • Meets Euro 6d-Temp comfortably; needs cold-start NOₓ < 60 mg/km on RDE; close-coupled TWC + GPF + electric-pre-heated cat handles it under Euro 7 (2027).

8. Subsystems

Intake

  • SI: throttle valve (electronic, drive-by-wire), MAF sensor (hot-wire/film) or MAP+IAT, intake manifold runner control (IMRC, tumble flap), charge cooler (water-to-air on premium, air-to-air on cost-sensitive).
  • CI: no throttle (load = fuel quantity); MAF only for EGR control. VGT, twin-stage turbo for HD.

Exhaust + aftertreatment

  • Gasoline modern: close-coupled TWC (Pt-Pd-Rh on cordierite, OSC = ceria/zirconia) + GPF (cordierite wall-flow, often catalysed). On Euro 7 and electrified strategies, electrically heated catalyst (EHC) upstream (e.g. Vitesco/Faurecia 3–5 kW, 48 V) for cold-start light-off in <10 s.
  • Diesel modern: DOC + DPF + SCR + ASC. HD-on-road 2027 architecture: close-coupled SCRF + dosing + underfloor SCR + ASC.

Lubrication

  • Wet-sump (98 % road), dry-sump (race, off-road, some performance V8s, all turbines).
  • Gerotor or vane oil pump, electronic-variable-displacement on modern (BMW N-series, GM Ecotec) — reduces parasitic loss by 0.5–1 % BSFC.
  • Oil viscosity grades: 0W-20 / 5W-30 dominant 2020+ for fuel economy; 5W-40 / 0W-40 turbo-performance; 15W-40 HD CK-4/FA-4 HDD; low-SAPS (low Sulfated-Ash, Phosphorus, Sulfur; ACEA C-grade, dexos2/dexos D) for aftertreatment compatibility.

Cooling

  • Water/glycol jacket in block + head, cross-flow or down-flow radiator, mechanical pump (belt-driven) traditional. Modern: electric coolant pump (BMW, since 2007), enables full thermal management — block warm-up by-pass, head/block split cooling (Ford 1.5 EcoBoost has split-cooling head + block separately temperature-controlled), heat-to-passenger-cabin in HEV winter operation.
  • Thermostat: 87–90 °C historical; modern fuel-econ engines run 105–110 °C “hot” thermostat at part-load, dropping to 90 °C at full load (mapped electric thermostat).

Ignition (SI)

  • Coil-on-plug (COP) — one ignition coil per spark plug, mounted on top of the plug. Universal since ~2005.
  • Iridium/platinum tip plug — 100 000–160 000 km service interval.
  • Multi-strike, multi-charge (dwell-current modulation) used at idle for stable lean burn (HCCI/SPCCI, Atkinson).

Starting

  • 12 V conventional starter — pinion-on-flywheel ring-gear, ~1.0–1.5 kW peak draw.
  • 48 V BSG (belt-starter-generator, P0 architecture) — silent stop-start, low-speed boost, regen.
  • 48 V ISG (integrated-starter-generator, P1 between engine and clutch, or P2 between clutch and gearbox) — torque smoothing, more regen, sail mode. Mercedes EQ Boost M256/M264.

Fuel system

  • Gasoline PFI: lift pump in tank, 3–5 bar regulated, return-less rail.
  • Gasoline GDI: low-pressure lift pump (5 bar) + cam-driven high-pressure pump (100–350 bar) feeding common rail of solenoid injectors.
  • Diesel CR: lift pump (4–6 bar) + cam-driven HPFP (CP4, CP1H, Denso HP4) to 1500–2700 bar rail feeding piezo or solenoid injectors. CP4 wear under low-lubricity diesel (esp. US ULSD pre-2007 conditioning) caused widespread Bosch CP4 failures in Ford 6.7 Power Stroke and GM Duramax LML; class-action suits 2018+.

ECU

  • Multi-core MCU: Infineon AURIX TC3xx (e.g. TC397) and NXP S32G dominate 2020s. Lockstep cores for ISO 26262 ASIL-B/D. Software: AUTOSAR Classic for legacy, AUTOSAR Adaptive for newer compute-heavy (predictive thermal, OBD-on-board-monitoring of Euro 7). Calibration via ETAS INCA + ASAM MCD-2 MC (XCP-on-Ethernet/CAN-FD) or Vector CANape. See microcontrollers, realtime-embedded, and planned automotive-onvehicle.

9. Emissions and standards

Regulated pollutants: NOₓ (NO + NO₂), CO, HC (THC, NMHC, NMOG), PM (mass) + PN (particle number, ≥23 nm; Euro 7 + EPA HD Phase 3 drop to ≥10 nm), CO₂ / fuel-economy (CAFE in US, fleet-average g CO₂/km in EU/UK/CN).

Region / classStandardEffectiveHeadline limits
Light-duty, EUEuro 6d-ISC-FCM2021–202660 mg/km NOₓ gas, 80 mg/km NOₓ diesel; PN 6×10¹¹/km; RDE conformity factor ≤ 1.43
Light-duty, EUEuro 71 Jul 2027 LD, 2029 HDSame NOₓ cap; PN ≥ 10 nm; brake PM 7 mg/km; OBM over useful life; −10 °C cold-start; battery durability provisions for HEV/PHEV
Light-duty, US fedEPA Tier 3 + CARB LEV III2017–2025Fleet avg 30 mg/mi NMOG+NOₓ by 2025 (Bin 30); PM 3 mg/mi
Light-duty, USEPA “Tier 4” rule + CARB LEV IV2027–2032 phase-inTighter PM, GHG; aligning with Euro 7 spirit but separate test
HD on-road, USEPA HD Phase 3 / CARB Omnibus2027 MY0.035 g/bhp·hr NOₓ (–82 %), GHG cut, useful life 650 000 mi
HD on-road, EUEuro VI-E → Euro VIIcurrently Euro VI-E; Euro VII 2028 LD HDV / 2029 heavyCold-start hot-cycle PEMS, similar NOₓ ratchet to EPA HD Phase 3
Non-roadEPA Tier 4 Final / EU Stage V2014/2019DPF required ≥56 kW
MarineIMO MARPOL Annex VI Tier I/II/IIITier III since 2016 in NECAs (Baltic, North Sea, NA-ECA)Tier III NOₓ 3.4 g/kWh @ rated rpm < 130 rpm; IMO 2020 fuel sulfur 0.5 % global (0.1 % in SECA); EU CII since 2023 — carbon-intensity rating for ships
LocomotiveEPA Tier 4 (rail)Since 2015DPF + SCR equivalent emissions per bhp-hr

SI aftertreatment chemistry — Three-way catalyst (TWC):

  • Oxidation: CO + ½O₂ → CO₂; HC + O₂ → CO₂ + H₂O
  • Reduction: 2NO + 2CO → N₂ + 2CO₂; 2NO + 2H₂ → N₂ + 2H₂O
  • Requires λ = 1 ± 0.01 — managed by closed-loop UEGO upstream + switching HEGO downstream feedback trim
  • OSC (oxygen storage capacity, ceria-based) buffers brief lean/rich excursions
  • Light-off: 250–350 °C

CI aftertreatment chemistry — SCR with urea (Standard, Fast, NO₂):

  • Standard SCR: 4NH₃ + 4NO + O₂ → 4N₂ + 6H₂O
  • Fast SCR: 2NH₃ + NO + NO₂ → 2N₂ + 3H₂O (preferred — DOC oxidises NO to NO₂)
  • NO₂ SCR: 4NH₃ + 3NO₂ → 3.5N₂ + 6H₂O (slow)
  • Bed temperature: 200–500 °C optimal; copper-zeolite (Cu-CHA, SSZ-13) for low-T, iron-zeolite (Fe-MFI) for high-T HD. Ammonia slip catalyst (ASC, Pt-based) downstream catches breakthrough NH₃.

10. Alternative and future fuels

FuelLHV (MJ/kg)Notes
Gasoline (RON 95)43.4Reference. AKI 87–93 US, RON 95–98 EU.
Diesel No. 2 (ULSD ≤ 15 ppm S)43.0Cetane ≥ 40 US, ≥ 51 EU.
Ethanol (E100)26.8RON 109 — knock-tolerant. E10 mandatory most of EU, E15 push in US (2023 EPA summer waiver), E85 flex-fuel. Brazil flex-fuel ~76 % of new car sales.
Methanol19.9RON 109. China M85/M100 trials in Shanxi. Maersk has methanol-burning containerships ordered (1st delivery 2024 Laura Maersk).
Biodiesel (FAME)37.2B5 / B7 (EU EN 590 cap 7 vol %), B20 in US fleet. Higher NOₓ vs. petrodiesel; cold-flow issues.
HVO (renewable diesel, NEXBTL)44.0Drop-in to existing CI engines, EN 15940 paraffinic. ~85 % WtW CO₂ reduction.
CNG (~methane)50.0 (mass), ~9 (vol @ 200 bar)UPS, transit bus, refuse truck. Stoichiometric SI or HPDI dual-fuel diesel (Westport).
LNG50.0Marine + heavy-haul (Volvo G13, Scania OC13). Methane slip is the headache — IMO + EU regulating.
LPG (propane/butane mix)46.1Forklifts, taxi fleets EU/Asia. SI bi-fuel converters.
Hydrogen H₂120 (LHV)Toyota Corolla H2 (Super Taikyu 2021), Cummins X15H (announced 2023, prod 2025), JCB hydrogen engine 2022. Zero-CO₂; NOₓ remains. Direct-injection at λ > 2 keeps NOₓ low.
Ammonia NH₃18.6Marine dual-fuel pilot ignition (MAN B&W ME-LGIA, Wärtsilä 25 NH₃). Toxicity, low CN handled by diesel pilot. First commercial NH₃-burning ships 2025–2027 deliveries.
e-fuels (synthetic petrol/diesel)≈ 43Drop-in. Porsche/HIF Haru Oni 2022 pilot, Chile. Cost ≥ 5× fossil today; viable only with carbon pricing + cheap green H₂.

11. Tools and software

Cycle / system simulation (1-D):

  • GT-Power + GT-SUITE (Gamma Technologies) — industry standard, full vehicle/powertrain, includes vehicle dynamics, aftertreatment kinetics, HEV/EV. Used by ~all major OEMs.
  • AVL BOOST — 1-D gas dynamics, sister tools FIRE (3-D CFD), ASTERICS, CRUISE (vehicle/HEV).
  • Ricardo WAVE — 1-D gas dynamics + combustion sub-models. WaveBuild GUI.
  • Mahle PowerCool / AMESim (Siemens) — also used.

3-D CFD for in-cylinder combustion + sprays:

  • Converge CFD (Convergent Science) — automatic adaptive mesh, dominant for engine CFD since ~2015.
  • STAR-CCM+ “ICE Module” (Siemens) — automotive standard CFD with engine-specific physics.
  • ANSYS Forte — derived from KIVA, automated meshing.
  • KIVA (Los Alamos) — open code, declining commercial use but seed of much modern engine CFD.

Chemistry / combustion kinetics:

  • Cantera (open source) — gas-phase kinetics, transport, equilibrium.
  • CHEMKIN-PRO (Ansys) — gold-standard kinetic mechanism solver.
  • Mechanisms: GRI-Mech 3.0 (natural gas), LLNL n-heptane / iso-octane / PRF / TRF, KAUST surrogate, ERC reduced mechs.

Test cells + emissions instrumentation:

  • AVL, Horiba, Schenck, FEV, Sierra-CP — dyno benches, eddy-current and AC absorbers.
  • Emissions analyzers: Horiba MEXA-7000, AVL AMA i60 (FTIR for NH₃/N₂O speciation), AVL APC for PN.
  • Portable: PEMS (Sensors Inc. SEMTECH, Horiba OBS-ONE) for RDE and HD on-road compliance.
  • Indicating: AVL GU22C or Kistler 6041A piezo cylinder-pressure transducer, AVL IndiCom.

Calibration:

  • ETAS INCA + INCA-FLOW automation, ASAM XCP-on-Ethernet/CAN-FD.
  • Vector CANape + CANalyzer.
  • dSPACE ControlDesk, RTI Bypass for rapid prototyping ECU strategies.
  • DoE optimisation: AVL CAMEO, ETAS ASCMO, MATLAB Model-Based Calibration Toolbox (Gaussian-process surrogates).

HEV integration:

  • MATLAB/Simulink + Simscape — universal industry plant model and control prototyping.
  • AVL CRUISE-M / GT-SUITE — vehicle-level co-sim.

OBD diagnostic tools:

  • Bosch KTS workshop scan tool, Snap-on Modis/Zeus, Autel MaxiSys.

12. Edge cases and failure modes

  • Knock + LSPI — turbo-GDI Achilles’ heel. LSPI mitigation requires API SP / ILSAC GF-6 / dexos1 Gen 3 oils with Ca-Mg reformulated detergents.
  • DPF ash loading — non-regenerable. Drives shift to ultra-low-SAPS oils. ash-volume-monitoring (model-based, mileage + active-regen-frequency).
  • AdBlue counterfeit / dilution — water-only or below-spec urea cuts SCR effectiveness, triggers OBD MIL + driving-distance derate (5 mph “limp-home” inducement on US HDV per CARB). VW MQB diesel field issue 2020–2022.
  • Cold-start cat light-off — 70+ % of regulated emissions over US FTP-75 occur in first 60 s before TWC reaches 350 °C. Mitigation: retarded ignition + lean idle to dump enthalpy into exhaust, secondary air injection (BMW N62, Toyota), electric heated cat (Euro 7 standard).
  • HPFP wear (CP4 / CP4.2) — Ford 6.7 Power Stroke, GM 6.6 Duramax LML/LGH 2011+. Diesel lubricity standard ASTM D6079 HFRR 520 µm; CP4 sensitive when contaminated water + ULSD interact. Class-action settled 2024.
  • Cylinder deactivation NVH — GM AFM/DFM, Chrysler MDS, VW ACT, Mercedes Cylinder-on-Demand. Booming at 30–80 Hz in deactivated mode mitigated by active engine mounts (electro-hydraulic or magnetorheological) and active noise cancellation through audio system (Bose ANC).
  • VW Dieselgate (September 2015) — defeat-device EA189 and EA288: ECU detected NAS dyno cycle (steering-angle = 0, speeds matching FTP) and ran a clean calibration; on the road, dumped EGR and SCR-dose to protect components, NOₓ 10–40× over limit. $33 B+ in fines/settlements; criminal convictions; permanently changed EU policy → mandatory RDE PEMS testing.
  • Catalyst aging — PGM sintering (Pt/Pd/Rh particle coarsening, ~600 °C+) reduces active surface; quantified by oxygen-storage-capacity (OSC) diagnostic. Useful life: 150 000 mi (Tier 3) → 250 000 mi (Tier 4 spec).
  • Lambda sensor life — 100–150 000 km typical; planar wide-band UEGO degrades by Pt-electrode erosion + lead/phosphorus contamination. Drift compensated by downstream-sensor adaptation.
  • Crankshaft TVD / damper failure — VW EA189 2010+ flex-plate cracks; harmonic damper (rubber Geislinger or viscous Vibratech) hardens with age, lets torsional mode reach the crank flange.
  • Wet-belt failure — Ford EcoBoost belt-in-oil cam drive (1.0 + 1.5 EcoBoost) — belt strands shed into oil, clog screen, starve pump. Class actions ongoing.
  • 48 V mild-hybrid BSG belt slippage — high transient regen torque (50–80 N·m) overloads accessory belt; resolved by wedge-pulley or by moving to P1/P2 architectures.
  • HCCI/SPCCI control window — narrow; requires fast intake-cam phasing + cylinder-pressure feedback (in-cylinder pressure sensing standard on SkyActiv-X via integrated glow-plug-style PS).

13. Cross-references

14. Citations

Textbooks (canonical):

  • Heywood, J. B. Internal Combustion Engine Fundamentals, 2nd ed., McGraw-Hill, 2018. The reference.
  • Stone, R. Introduction to Internal Combustion Engines, 4th ed., Palgrave Macmillan, 2012.
  • Pulkrabek, W. Engineering Fundamentals of the Internal Combustion Engine, 2nd ed., Prentice Hall, 2003.
  • Ferguson, C. R., Kirkpatrick, A. T. Internal Combustion Engines: Applied Thermosciences, 3rd ed., Wiley, 2015.
  • Bosch Automotive Handbook, 11th ed., Wiley/Bosch, 2022.
  • Merker, Schwarz, Stiesch, Otto. Simulating Combustion: Simulation of combustion and pollutant formation for engine-development, Springer, 2006.

Historical patents and seminal papers:

  • Otto, N. A. German patent DRP 532, 1876 — four-stroke cycle.
  • Diesel, R. German patent DRP 67207, 1893 — compression-ignition cycle.
  • Atkinson, J. UK patents 2078/1882 and 1985/1887 — overexpansion cycle.
  • Miller, R. H. US Patent 2,773,490, 1957 — late intake valve closure with supercharging.
  • Wankel, F. German patent applications 1929+; first prototype 1957 (NSU).
  • Zeldovich, Ya. B. Acta Physicochim. URSS 21, 577, 1946 — thermal NOₓ mechanism.
  • Lavoie, G. A., Heywood, J. B., Keck, J. C. Combust. Sci. Technol. 1, 313, 1970 — application of Zeldovich to SI engines.
  • Ricardo, H. R. The Internal Combustion Engine, Blackie, 1923.

Standards:

  • SAE J1349 (rev 2021) — Engine power test code, spark-ignition + compression-ignition net power rating.
  • SAE J2723 (rev 2022) — Engine power test code certification procedure.
  • EPA Tier 3 light-duty (40 CFR Part 86, 2014); EPA HD Phase 3 GHG + NOₓ (2024 final rule, 2027 MY).
  • Regulation (EU) 2018/858 + (EU) 2017/1151 (RDE), Euro 6d-ISC-FCM; Regulation (EU) 2024/1257 — Euro 7.
  • UN ECE GTR No. 15 (WLTP), GTR No. 17 (EVAP).
  • IMO MARPOL Annex VI Reg. 13 (NOₓ) and Reg. 14 (SOₓ); IMO 2020 sulfur cap; IMO EEXI/CII.

Vendor + OEM technical disclosures:

  • Cummins X15 Efficiency series (2024) public spec sheet.
  • Volvo D13TC turbo-compounding SAE paper 2019-01-2284.
  • Detroit DD15 Gen 5 (2022) press kit + SAE 2022-01-0586.
  • Porsche / HIF Haru Oni e-fuel pilot 2022 press release + EU FCH-JU report.
  • Mazda SkyActiv-X SPCCI: Kim et al., SAE 2019-01-0967.
  • Toyota Atkinson-cycle hybrid engines: SAE 2017-01-1014 (A25A-FXS).
  • MAN Energy Solutions S60ME-C8.5 project guide, 2023.

Software references:

  • GT-SUITE User’s Manual, Gamma Technologies, v2024.
  • AVL BOOST User’s Guide, AVL List GmbH, 2024.
  • Converge CFD Manual v3.1, Convergent Science, 2024.
  • Cantera 3.0 documentation, https://cantera.org

Built as part of the Engineering Tier 2 deep-note series. Sibling notes: thermodynamics (foundational), propulsion (alternative reaction engines).

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