Mechanical Hybrid · Hydrogen Enrichment

Wankel Rotary Engine Hybrid System

A comprehensive technical reference for integrating PEM hydrogen electrolysis with Wankel rotary engines. Gasoline priority with on-demand H₂/O₂ enrichment for improved combustion efficiency and dramatically reduced emissions. Featuring coaxial counter-rotating copper wheel alternators (outer and inner wheels on the same axis, spinning in opposite directions) driven from the Wankel bottom output shaft, plus a gas compression-expansion water recovery system that condenses exhaust moisture to feed the electrolyzer.

Cutaway view of a Wankel rotary engine showing the triangular rotor inside the epitrochoid housing

48%

CO Reduction

34%

Efficiency Gain

77%

CO₂ Reduction

90%

NOx Mitigation

System Architecture

Power flow through the Wankel H₂ hybrid drivetrain.

How It Works

The mechanical hybrid architecture prioritizes gasoline while using surplus power for hydrogen production.

Gasoline Primary

The Wankel engine runs on gasoline as primary fuel. The bottom output shaft drives a coaxial counter-rotating copper wheel alternator — two concentric rings spinning in opposite directions on the same axis.

Water → H₂ + O₂

The PEM electrolyzer splits water into hydrogen and oxygen. Water is supplied by the gas compression-expansion recovery system that condenses moisture from exhaust, supplemented by an onboard tank.

Enhanced Combustion

Hydrogen and oxygen are injected back into the engine, improving flame speed, enabling leaner combustion, and reducing CO, HC, and CO₂ emissions significantly.

Passenger Vehicle Configuration

Single Engine Car Configuration

A compact hybrid architecture featuring one Wankel rotary engine. The bottom output shaft drives both the differential (for the wheels) and a coaxial counter-rotating copper wheel alternator — two concentric copper rings on the same axis spinning in opposite directions — that generates DC power for the PEM electrolyzer. Exhaust gases pass through a compression-expansion condenser that recovers water to feed back into the electrolyzer.

System Specifications

⚙️ Engine Type

2-Rotor Wankel, 1,308 cc

⏱ Peak Power

~180 HP @ 6,500 RPM

🔁 Operating Speed

2,000 – 6,500 RPM

🔋 Alternator Output

10 – 15 kW DC

💧 H₂ Production

0.18 – 0.27 kg/h

🔥 O₂ Production

1.46 – 2.18 kg/h

🌡 Electrolyzer Temp

60 – 80°C

⚖️ System Weight Add

~35 – 50 kg

Power Distribution

⚡ Mechanical Path (~85%)

• Bottom output shaft connects to transmission
• Standard differential distributes torque to wheels
• Direct mechanical coupling — no energy conversion losses
• Brake thermal efficiency improved with H₂ enrichment

⚡ Electrical Path (~15%)

• Coaxial copper wheels (same axis, opposite spin) generate AC → rectified to DC
• DC bus distributes to electrolyzer + auxiliaries
• PEM electrolyzer splits H₂O at ~55 kWh/kg efficiency
• ECU-controlled H₂/O₂ injection back into engine intake

Gas Mixture System

Gasoline remains the primary fuel source. At cruise, gasoline accounts for 85–95% of total fuel energy input. The Wankel engine's continuous combustion cycle provides smooth, high-RPM operation well-suited to gasoline fueling.

H₂ produced on-demand by the PEM electrolyzer. Flame speed ~8× faster than gasoline enables leaner mixtures (lambda up to 1.6). Injected during the intake stroke for thorough mixing before ignition.

O₂ byproduct enriches the combustion air charge. Caution: Must be carefully metered to avoid NOx spikes. ECU limits O₂ injection based on real-time NOx sensor feedback. Maximum 4% of intake mass flow.

Water Recovery: Gas Compression-Expansion

💧

Instead of relying solely on an external water tank, the system recovers water from engine exhaust using a gas compression-expansion condenser. Combustion of gasoline and hydrogen produces significant water vapor (H₂O) in the exhaust stream.

How It Works

→ Exhaust gas exits the Wankel engine at 400–700°C containing H₂O vapor
→ A compressor stage raises gas pressure, increasing the dew point
→ The gas is cooled through an expansion stage and heat exchanger
→ Water condenses out and is collected, filtered, and deionized
→ Recovered water is fed directly to the electrolyzer bank

Recovery Rates

Gasoline combustion~1.4 kg H₂O per kg fuel

H₂ combustion~9.0 kg H₂O per kg H₂

Recovery efficiency~30–50% of exhaust H₂O

Car: typical recovery~0.5–1.0 kg/h H₂O

Bus: typical recovery~1.5–3.0 kg/h H₂O

Tank refill reduction~25–40% less frequent

PEM Electrolyzer Detail

Cross-sectional diagram of a PEM electrolyzer showing water splitting into H₂ and O₂

The PEM electrolyzer is the heart of the hydrogen generation subsystem. It uses DC electricity from the coaxial alternator to split water — both recovered from exhaust and from the onboard tank — into hydrogen and oxygen.

Energy Consumption~55 kWh per kg H₂

Stack Efficiency~65% (LHV basis)

Cell Voltage1.9 V per cell

Water SourceRecovered + Tank

Response Time<1 second to load change

Heavy-Duty Transit Configuration

Dual Engine Bus Configuration

Two counter-rotating Wankel engines, each with its own coaxial counter-rotating copper wheel alternator (concentric rings on the same axis). Both alternators feed a shared DC bus powering a high-capacity PEM electrolyzer bank. A shared gas compression-expansion water recovery unit collects exhaust condensate from both engines.

System Specifications

⚙️ Engines

2× 2-Rotor Wankel, 1,308 cc each

⏱ Combined Power

~360 HP @ 6,500 RPM

↔ Configuration

Counter-Rotating

🔋 Alternator Output

2× 12–15 kW DC

💧 H₂ Production

0.44 – 0.55 kg/h

🔥 O₂ Production

3.5 – 4.4 kg/h

🌡 Cooling System

Dual-loop liquid cooled

⚖️ System Weight Add

~80 – 120 kg

Why Coaxial Counter-Rotating Wheels?

↔

Same-Stage Design

Both copper wheels share the same axis — outer ring CW, inner ring CCW. Compact coaxial packaging saves space and weight vs. side-by-side layouts.

🔰

Vibration Cancellation

Concentric counter-rotation on a single axis perfectly cancels gyroscopic torque and reduces drivetrain vibration for passenger comfort.

⚡

Doubled Relative Speed

The relative angular velocity between the inner and outer rings is effectively doubled, generating more electrical output from the same shaft RPM.

Car vs. Bus Comparison

Parameter	Car (Single)	Bus (Dual)
Engines	1× 13B (1,308 cc)	2× 13B (2,616 cc total)
Peak Power	~180 HP	~360 HP
Alternators	1× coaxial CR pair	2× coaxial CR pairs
Electrolyzer Power	10–15 kW	24–30 kW
H₂ Production	0.18–0.27 kg/h	0.44–0.55 kg/h
Water Consumption	1.6–2.4 kg/h	4.0–5.0 kg/h
Water Recovery	0.5–1.0 kg/h	1.5–3.0 kg/h
Torque Balance	Single coaxial CR	Dual coaxial CR + engine CR
Target Application	Sedan / Compact	Transit Bus / Heavy Duty

🔢 Engineering Reference

Engineering Calculations

Power output formulas, electrolyzer sizing, hydrogen production rates, and combustion efficiency analysis.

Engine Power Output

P = 2πNT / 60
P = power (W), N = speed (rpm), T = torque (N·m)

For a 13B engine at 6,500 RPM with 190 N·m torque:

P = 2π × 6500 × 190 / 60 = 129,330 W ≈ 129.3 kW (173 HP)

Shaft Power Distribution

P_shaft = P_wheel/η_drive + P_elec/η_alt
η_drive = driveline eff., η_alt = alternator eff.

With P_wheel = 80 kW, η_drive = 0.93, P_elec = 10 kW, η_alt = 0.90:

P_shaft = 80/0.93 + 10/0.90 = 97.1 kW required

Performance Comparison

Baseline BTE

28%

H₂ Enriched BTE

38%

CO Reduction

-48%

HC Reduction

-22%

CO₂ Reduction

-77%

NOx Mitigation

-90%

Electrolyzer Sizing

ṁ_H₂ = P_elec / SEC
ṁ_H₂ = kg/h, P_elec = kW, SEC = kWh/kg

Faraday's Law

ṁ_H₂ = η_F × I × M_H₂ / (2F)
F = 96,485 C/mol, M_H₂ = 2.016 g/mol

Engineering constant: 1 A·h ≈ 0.0376 g H₂

Key Constants

1 kg H₂11.1 Nm³

1 kg H₂ needs9 kg water

1 kg H₂ produces8 kg O₂

H₂ LHV33.3 kWh/kg

H₂ HHV39.4 kWh/kg

Stoich. air for H₂34.3 kg/kg H₂

Interactive Calculator

Alternator Power: 10 kW

⚗ H₂ Production Rate0.1818 kg/h

🧪 H₂ Volume Flow2.02 Nm³/h

🔥 O₂ Byproduct1.455 kg/h

💧 Water Consumption1.636 kg/h

H₂ Production vs. Power

Power (kW)	H₂ (kg/h)	H₂ (Nm³/h)	O₂ (kg/h)
5	0.091	1.01	0.727
10	0.182	2.02	1.455
15	0.273	3.03	2.182
20	0.364	4.04	2.909
25	0.455	5.05	3.636
30	0.545	6.06	4.364
50	0.909	10.09	7.273

Emission Reductions

-48%

-22%

CO₂

-77%

NOx

-90%

Smoke Opacity

-34%

Combustion Benefits

Brake Thermal EfficiencyUp to +34%

CO EmissionsUp to -48%

HC EmissionsUp to -22%

CO₂ EmissionsUp to -77%

Smoke OpacityUp to -34%

Why H₂ Improves Combustion

→ Flame speed ~8× faster than gasoline
→ Wide flammability limits (4–75% in air)
→ Extremely low ignition energy (~0.02 mJ)
→ Reduces cycle-to-cycle variation

🛡️ Safety Engineering

Safety Systems

Multi-layered safety architecture covering leak detection, pressure management, thermal control, and NOx emission mitigation.

Hydrogen Properties

⚠️

Hydrogen is colorless, odorless, and highly flammable with near-invisible flames. Its extremely low ignition energy and wide flammability range demand rigorous engineering controls.

Lower Flammability Limit4% by volume in air

Upper Flammability Limit75% by volume in air

Minimum Ignition Energy~0.02 mJ

BuoyancyVery high — rises rapidly

Design Target<1% accumulation

Flame VisibilityNearly invisible in daylight

Multi-Layer Safety Architecture

👁

Leak Detection

Multiple hydrogen sensors at high points and enclosed cavities. Catalytic bead and electrochemical sensors provide redundant detection with <1 second response time.

🔒

Automatic Shutoff

Fail-safe solenoid valves on all hydrogen lines. Triggered by leak detection, crash sensors, overpressure, or ECU fault. Spring-loaded to close on power loss.

📊

Pressure Management

Thermally-activated pressure relief devices (TPRDs) on buffer tanks. Burst discs sized for worst-case thermal runaway. Operating pressure: 1–2 bar above intake manifold.

💨

Ventilation

Forced-air ventilation in all enclosed compartments. Vent routing directs any released H₂ upward and away from occupants. ATEX-rated fans and ducting.

🌡

Temperature Control

Dual-loop liquid cooling for electrolyzer (60–80°C) and engine. Temperature sensors on all H₂ lines, buffer tanks, and electrolyzer stack. Auto-shutdown above 95°C.

📈

Continuous Diagnostics

Real-time monitoring during operation, parking, and shutdown. Fault codes for sensor degradation, seal wear, and performance drift. OBD-II compatible reporting.

NOx Emission Mitigation

Operating at lambda 1.3–1.6 lowers peak flame temperature. Hydrogen's wide flammability limits make this practical without misfires. Combined NOx reduction of 50–70%.

EGR rates of 10–20% dilute the intake charge. Combined with lean burn, NOx reduction of 60–80%. Reduces peak combustion temperature without affecting power output significantly.

5–10% water by fuel mass absorbs heat through evaporation. Synergistic with the electrolyzer's water supply. Combined NOx reductions exceeding 90% when used with lean burn and EGR.

Three-way catalyst for stoichiometric operation. SCR with urea injection or lean NOx trap for lean-burn operation. Final layer in the defense-in-depth NOx mitigation strategy.

Materials & Standards

🛡️ Material Requirements

• H₂-embrittlement-resistant alloys for all wetted components
• Oxygen-clean stainless steel (316L) for O₂ lines
• PTFE or FKM seals rated for H₂ service
• Flame arrestors at all tank outlets

🔒 Standards & Compliance

• Tank proof/burst testing per applicable standards
• Crash integrity testing for all gas storage
• ATEX-rated electrical components in gas zones
• Purge procedures documented for maintenance

🖥️ Engine Management

Control Logic

The ECU manages fuel, hydrogen, and oxygen injection ratios in real-time, coordinating with the electrolyzer power control and emissions feedback.

⏱ Manifold Absolute Pressure (MAP)

Determines engine load for fuel/H₂ ratio calculation

🌡 Intake Air Temperature (IAT)

Compensates air density for stoichiometry

🌡 Coolant Temperature (ECT)

Adjusts enrichment during warm-up, protects electrolyzer

📊 Exhaust Lambda Sensor

Closed-loop air-fuel ratio control, lean-burn targeting

📊 NOx Sensor

Real-time NOx feedback for O₂ injection limiting

⏱ H₂ Buffer Tank Pressure

Prevents injection below minimum pressure threshold

⏱ O₂ Buffer Tank Pressure

Controls O₂ injection rate and venting decisions

🌡 Electrolyzer Stack Temp

Thermal protection; derate if >85°C, shutdown >95°C

📡 Throttle Position Sensor

Driver demand signal for power distribution

📊 Knock Sensor

Detects detonation; retards timing or reduces H₂ if triggered

🔥 Gasoline Injectors

Primary fuel delivery; pulse-width modulated per cycle

💧 H₂ Injectors

Hydrogen injection into intake; timing synced to intake port opening

⚡ O₂ Injectors

Controlled oxygen enrichment; rate-limited by NOx feedback

⚙️ Electrolyzer Power Control

PWM control of DC bus power to electrolyzer stack

⏱ EGR Valve

Exhaust gas recirculation rate for NOx control

💧 Water Injection Valve

Intake water injection for thermal NOx suppression

Fuel / H₂ / O₂ Ratio Management

📊 Operating Modes

Cold Start

G:100%H₂:0%O₂:0%

Electrolyzer off until coolant >40°C

Warm-Up

G:95%H₂:5%O₂:~1%

Gradual H₂ introduction

Cruise

G:85–90%H₂:8–12%O₂:2–4%

Lean-burn with full H₂ enrichment

Acceleration

G:92–95%H₂:5–8%O₂:0–1%

Prioritize gasoline; limit O₂ for NOx

Deceleration

G:cutH₂:0%O₂:0%

Max electrolyzer power (regen opportunity)

⏰ Injection Timing

Gasoline Injection

Port injection timed to intake port opening. Pulse width controlled by MAP, RPM, and lambda feedback.

Hydrogen Injection

Timed injection into intake manifold during intake stroke. Starts 30–60° before intake port opens for thorough mixing.

Oxygen Injection

Continuous low-rate upstream of throttle body. Rate-limited by real-time NOx sensor. Max 4% of intake mass flow.

Sequencing Priority

H₂ first → Gasoline second → O₂ blended last. Maximizes flame speed benefit.

Power Distribution Logic

⚡ Alternator Load Control

IF throttle_position > 80%: alternator_load = MIN_LOAD // Prioritize mechanical power ELSE IF speed > 0 AND throttle_position < 10%: alternator_load = MAX_LOAD // Decel regen ELSE: alternator_load = f(MAP, RPM, battery_SOC)

⚠ Safety Interlocks

→ H₂ leak detected → Full system shutdown

→ Knock detected → Retard timing + reduce H₂

→ NOx > limit → Reduce O₂, increase EGR

→ Overpressure → Stop electrolyzer + vent

→ Coolant overheat → Reduce power + alert

→ ECU comms fault → Fail-safe gasoline-only

Bus-Specific Control Logic

Dual Engine Synchronization

The bus ECU manages both engines as a synchronized pair. Counter-rotation maintained by independent speed control with torque-matching to within 2%.

If one engine must be shut down, the ECU smoothly transitions to single-engine mode with appropriate alternator load reduction.

Distributed H₂/O₂ Delivery

Both engines draw from a shared H₂ buffer tank via individual injectors. The ECU balances injection quantities based on each engine's MAP and RPM feedback.

The larger electrolyzer bank (24–30 kW) can be segmented: if one alternator fails, the other powers a reduced section maintaining H₂ supply at a reduced rate.