Let’s go in full detail about Carbon Monoxide (CO) — especially its formation, effects, sources in automobiles, and how it’s controlled.
In this article:
- 1. What is Carbon Monoxide (CO)?
- 2. Formation of Carbon Monoxide
- 3. Source of CO in Automobiles
- 4. Typical Concentration in Vehicle Emissions
- 5. Effects of Carbon Monoxide on Health
- 6. Environmental Impact of Carbon Monoxide
- 7. Control of CO Emissions in Automobiles
- 8. Monitoring Carbon Monoxide
- 9. Summary Table
1. What is Carbon Monoxide (CO)?
Definition:
Carbon monoxide is a colorless, odorless, tasteless, and poisonous gas produced by the incomplete combustion of carbon-containing fuels (like petrol, diesel, wood, coal, or natural gas).
Chemical formula: CO
Molecular weight: 28 g/mol
It consists of one carbon atom and one oxygen atom, forming a very stable gas that’s difficult to detect without sensors — hence often called the “silent killer.”
2. Formation of Carbon Monoxide
When fuel burns in limited oxygen (incomplete combustion), not all carbon atoms get converted into carbon dioxide (CO₂).
Instead, some carbon atoms combine with only one oxygen atom to form CO.
This occurs when:
- There’s not enough oxygen in the air–fuel mixture.
- Combustion temperature is too low to oxidize CO to CO₂.
- Fuel–air mixing is uneven.
3. Source of CO in Automobiles
A. In SI (Spark Ignition / Petrol) Engines
- CO forms when the air–fuel mixture is rich (too much fuel, not enough air).
- Common during idling, acceleration, and cold start.
- The highest CO emission occurs in petrol engines due to incomplete combustion.
B. In CI (Compression Ignition / Diesel) Engines
- CO emission is much lower because diesel engines run on lean mixtures (excess air).
- However, under heavy load or poor atomization, CO may still form.
4. Typical Concentration in Vehicle Emissions
| Engine Type | CO Percentage in Exhaust (approx.) |
|---|---|
| SI Engine (without catalytic converter) | 1–8% |
| SI Engine (with catalytic converter) | 0.05–0.3% |
| CI Engine (Diesel) | 0.01–0.2% |
5. Effects of Carbon Monoxide on Health
Carbon monoxide is highly toxic even at low concentrations because it interferes with oxygen transport in the body.
Mechanism:
- CO binds with hemoglobin (Hb) in the blood to form carboxyhemoglobin (HbCO).
- HbCO is 300 times more stable than oxyhemoglobin (HbO₂).
- This prevents oxygen from being carried to cells and tissues, causing oxygen deprivation (hypoxia).
Health Effects Table:
| CO Concentration (ppm) | Exposure Time | Symptoms |
|---|---|---|
| 50 ppm | 8 hours | Slight headache, fatigue |
| 200 ppm | 2–3 hours | Headache, nausea |
| 400 ppm | 1–2 hours | Dizziness, confusion |
| 800 ppm | 45 minutes | Unconsciousness |
| 1600 ppm | 20 minutes | Death possible |
| 6400 ppm | 1–2 minutes | Fatal |
Chronic exposure may cause:
- Memory loss
- Heart problems
- Impaired coordination
6. Environmental Impact of Carbon Monoxide
While CO doesn’t cause direct environmental damage like CO₂ or NOₓ, it still contributes to:
- Smog formation: CO reacts with other pollutants and sunlight to form ground-level ozone (O₃).
- Greenhouse effects (indirect): CO can affect methane (CH₄) and ozone levels, influencing climate.
- Air quality deterioration: High CO levels in urban areas indicate poor combustion efficiency.
7. Control of CO Emissions in Automobiles
1️⃣ Engine Design and Control
- Maintain correct air–fuel ratio (14.7:1 for petrol): Prevents rich mixtures that produce CO.
- Electronic Fuel Injection (EFI): Ensures precise fuel delivery and complete combustion.
- Proper ignition timing: Optimizes combustion temperature.
2️⃣ Exhaust After-Treatment Devices
a. Catalytic Converter
- Installed in the exhaust system.
- Contains platinum (Pt), palladium (Pd), and rhodium (Rh) as catalysts.
- Converts CO into CO₂.
Reaction:
It can reduce CO by up to 90–95% in modern vehicles.
b. Air Injection System
- Adds extra air into the exhaust manifold.
- Helps oxidize CO to CO₂ before it leaves the tailpipe.
c. Oxygen Sensor (Lambda Sensor)
- Monitors oxygen level in exhaust gas.
- Adjusts air–fuel ratio electronically for optimal combustion.
3️⃣ Fuel Quality
- Use of unleaded and low-carbon fuels improves combustion.
- Ethanol blending (E10, E20) helps reduce CO because ethanol burns more completely.
8. Monitoring Carbon Monoxide
- CO Detectors: Used in garages or tunnels to measure CO concentration.
- Emission Testing: Periodic vehicle inspections measure CO levels to ensure compliance with emission standards.
Permissible CO Emission Limits (Approx.):
| Region | Standard | CO Limit (g/km) |
|---|---|---|
| India (BS-VI) | Petrol car | ≤ 1.0 |
| Europe (Euro 6) | Petrol car | ≤ 1.0 |
| USA (EPA Tier 3) | Petrol car | ≤ 1.0 |
9. Summary Table
| Aspect | Details |
|---|---|
| Name | Carbon Monoxide |
| Chemical Formula | CO |
| Color/Odor | Colorless, odorless, tasteless |
| Source | Incomplete combustion of fuel |
| Major Engine Type | High in SI (petrol), low in CI (diesel) |
| Health Effect | Reduces oxygen supply to body (toxic) |
| Control Methods | Catalytic converter, EFI, correct air–fuel ratio |
| Environmental Effect | Contributes to smog, ozone formation |
✅ In Short:
Carbon Monoxide (CO) is a toxic gas formed by incomplete combustion of fuel.
It is colorless and odorless, making it extremely dangerous.
In automobiles, CO emissions are highest in petrol engines with rich mixtures, and are controlled by catalytic converters, fuel injection systems, and proper tuning.
💡 Fun Fact:
A car running in a closed garage can produce enough CO to cause fatal poisoning in just 10–15 minutes — that’s why it’s called the “silent killer gas.”
Other courses:
