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HENTEK CAT Catalyst & Catalytic Converter Solutions

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Technical Route – Hybrid Electric Vehicle (HEV/PHEV) Aftertreatment

The Hybrid Aftertreatment Challenge

Hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs) present a fundamental challenge for emissions control: the internal combustion engine operates intermittently and at lower average loads than conventional vehicles. Extended electric-only operation allows the exhaust system to cool below catalyst light-off temperature (200–250°C). When the engine restarts, cold-start emissions recur – not just once per trip, but multiple times.

This unique duty cycle renders conventional close-coupled catalysts insufficient. The HEV/PHEV technical route requires active thermal management, electrically heated catalysts (eHC), and rapid light-off strategies to meet Euro 7, EPA Tier 3, and China 7 real-driving emissions (RDE) requirements.

The Hybrid Aftertreatment Pathway

Complete system architecture:
Engine → Electrically Heated Catalyst (eHC) → Close-coupled TWC → Underfloor GPF (GDI) → Tailpipe

Step 1: The Hybrid Cold-Start Problem

  • Conventional vehicles: one cold start per trip, engine keeps catalyst above light-off
  • HEVs/PHEVs: engine may start multiple times:
    • Initial cold start: warms catalyst
    • Electric-only driving: catalyst cools
    • Engine restart: cold catalyst, high emissions
  • Catalyst temperature can drop from 400°C → 100°C in 5–10 minutes of electric driving
  • Engine restart produces 60–80% of cold-start emissions

Step 2: Electrically Heated Catalyst (eHC) – Core Technology

  • Resistive heating element integrated into or upstream of TWC substrate
  • Maintains catalyst above light-off when engine is off
  • Rapidly reheats catalyst 300°C in <10 s when engine restarts

Construction:

  • Metallic foil substrate (FeCrAlloy) with printed resistive tracks
  • Ceramic substrate with embedded conductive grid (emergent)
  • 48V power supply (from hybrid battery)
  • Heater power: 1–4 kW depending on catalyst volume and target temperature

Operating modes:

  • Standby heating (200–400 W): maintains 150–200°C, minimal battery drain
  • Rapid reheat (2–4 kW): 150°C → 300°C in 5–10 s before engine restart
  • Cold-start assist (2–4 kW, 10–30 s): accelerates initial light-off from ambient → 300°C

Energy consumption:

  • Standby: 50–100 Wh per hour (acceptable for 10–20 kWh PHEV battery)
  • Rapid reheat: 5–10 Wh per restart
  • Cold-start assist: 15–30 Wh per trip
  • Total energy: <3% of typical PHEV battery capacity

Step 3: Thermal Management Strategy

Active control:

  • Sensors at eHC outlet and TWC inlet
  • PID-modulated eHC power maintains 300–350°C during engine-off
  • ECU predicts restart (accelerator, SOC, navigation) and pre-heats catalyst

Passive retention:

  • Insulation: ceramic fiber wrap, aerogel blanket
  • Heat storage: phase-change materials, high-specific-heat ceramics
  • Extends cool-down from 5–10 → 15–30 min
  • Close-coupled mounting minimizes heat loss

Engine calibration:

  • Delayed intake valve closing (Miller cycle) raises exhaust temp
  • Increased idle speed: 900–1,200 rpm during cold start
  • Reduced EGR to raise combustion temperature

Step 4: Three-Way Catalyst (TWC) for Hybrids

  • Low-temperature optimized: ceria-zirconia 40–50% of washcoat (vs 20–30%)
  • Lower PGM loading possible (eHC maintains temperature)
  • Faster light-off formulation: Pd-rich top layer, reduced diffusion barriers

Substrate:

  • Thin-wall metallic preferred for eHC integration
  • Lower thermal mass than ceramic: 300°C in 5–10 s
  • Cell density: 400–600 cpsi, wall thickness 2–3 mil

Volume optimization: engine displacement × 0.8–1.0 (vs 1.0–1.5 for conventional)

Step 5: GPF Integration for GDI Hybrids

  • Catalyzed GPF (cGPF / Four-Way Catalyst): TWC washcoat on wall-flow filter
  • Single brick saves space and weight
  • Passive regeneration sufficient (500–700°C)
  • Electric pre-heating of GPF ensures catalyst activity before engine restart

Step 6: Control Strategy – Predictive Thermal Management

Rule-based (current generation):

  • eHC activates if SOC >30% and engine-off >2 min
  • Catalyst temperature monitored; eHC engages if <200°C
  • Engine restarts if catalyst ≥150°C and driver power demand low

Predictive (next generation):

  • GPS & navigation predict electric-only range and engine restarts
  • ML learns driver behavior
  • Cloud-based route optimization maintains catalyst temperature
  • Pre-heating triggered before high power demands

Key Advantages of the Hybrid Route

Zero cold-start emissions potential: eHC keeps catalyst at light-off, compliant with Euro 7 RDE

Fuel economy without emissions penalty: engine operates only when optimal; no rich mixtures for heating

OBD compliance: catalyst monitor active, eHC electrical circuit monitored, DTCs for degradation

Scalable from HEV → PHEV → REEV: heater sized for frequent or extended engine-off periods

Our HEV/PHEV Aftertreatment Expertise

We engineer complete hybrid aftertreatment solutions:

  • 48V eHC-integrated metallic TWC for full hybrid sedan
  • Low-power standby heating for 50 km PHEV
  • Predictive thermal management controller for connected hybrid SUV

We tailor: eHC power (1–4 kW), substrate (metallic/ceramic), TWC formulation (high-OSC, fast light-off), insulation, and control algorithms to hybrid architecture, battery capacity, and regulatory target.

Partner with us to define your path to compliance – hybrid efficiency, catalyst readiness.

The Future of Hybrid Aftertreatment

Predictive eHC (cloud-connected)

Pre-heating scheduled for highway entrances, hills, passing zones; OTA updates optimize energy use

Phase-change material (PCM) thermal batteries

Store heat at 300°C, release during engine-off (extends cool-down 15 → 45+ min)

Integrated eHC + SCR (lean-burn hybrids)

Maintain SCR at 175°C for Cu-zeolite; critical for H₂-ICE hybrids

Zero-emission zone (ZEZ) compliance

PHEV operates electric-only; eHC or thermal battery ensures readiness for engine restart

The hybrid electric vehicle is not a conventional car with added battery – it is a fundamentally different platform requiring re-engineered aftertreatment. A well-designed HEV/PHEV system achieves zero cold-start emissions penalty, maintains catalyst readiness through hours of electric driving, and maximizes fuel economy without compromising compliance. Whether you are developing a Euro 7 PHEV or a China 7 full hybrid, our hybrid aftertreatment solutions deliver electric-range freedom with emissions confidence – and we are ready to engineer your solution.