What modifications are required in CI engine to use gaseous fuels? Explain ?

 

🔧 Modifications Required in CI Engines to Use Gaseous Fuels

Compression Ignition (CI) engines are originally designed to operate on liquid diesel fuel, which ignites by compression-induced auto-ignition. To use gaseous fuels (like CNG, LPG, biogas, or hydrogen), certain modifications are necessary because most gaseous fuels have different combustion properties, especially in terms of auto-ignition temperature and ignition delay.

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✅ Common Gaseous Fuels Used:

• CNG (Compressed Natural Gas)

• LPG (Liquefied Petroleum Gas)

• Hydrogen

• Biogas

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🔄 Types of Conversion Methods:

There are two primary methods to modify a CI engine for gaseous fuels:

1. Dual-Fuel Operation (Diesel + Gas):

• The engine runs on a mixture of diesel and gaseous fuel.

• Diesel acts as the pilot fuel to ignite the gas–air mixture.

2. Spark-Ignition Conversion:

• The engine is converted to a spark-ignition system.

• Used for 100% gaseous fuel operation, but involves more extensive modifications.

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🔧 Key Modifications Required:

Component	Modification/Adaptation
🛢️ Fuel Supply System	- Add gas storage tanks (CNG cylinders, LPG tanks, etc.)- Install pressure regulators, filters, and pipelines.- Include safety shut-off valves.
🔄 Fuel Mixing System	- Introduce gas mixing unit (mixer or carburetor) to blend gas with air.- Use electronic gas injectors for precise control (in advanced systems).
🔥 Ignition System	- In dual-fuel: retain diesel injector for pilot injection.- In spark-ignition conversion: install spark plug, ignition coil, and timing system.
🧠 Engine Control System	- Modify ECU/ECM to handle gas injection timing, throttle control, and pilot injection (if needed).- Add knock sensors for safety.
🛠️ Compression Ratio	- May need to reduce compression ratio if gas has high knock sensitivity (especially for LPG or CNG in full-conversion).
🔄 Valve Timing & Material	- Use valve seat hardening and heat-resistant materials, especially with dry-burning gases like hydrogen.
🌡️ Cooling System	- May need upgraded cooling due to higher combustion temperatures in some gases (e.g., hydrogen, biogas).

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⚙️ Working of a Dual-Fuel CI Engine:

1. Air and gas are mixed (externally or via manifold injection).

2. The mixture enters the cylinder during the intake stroke.

3. A small quantity of diesel (pilot fuel) is injected near the end of compression.

4. The diesel auto-ignites, which in turn ignites the gas–air mixture.

5. Combustion occurs as in conventional CI engines.

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✅ Advantages of Using Gaseous Fuels in CI Engines:

• Cleaner combustion: lower CO, HC, and PM emissions

• Reduced fuel cost (especially CNG or biogas)

• Better fuel-air mixing and smoother operation

• Renewable fuel use (biogas, hydrogen)

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❌ Challenges:

• Slight power loss (due to lower energy density of gases)

• Detonation/knock risk (especially with hydrogen or LPG)

• Needs precise control of air–fuel ratio and timing

• Storage and safety systems must be robust

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🧠 Conclusion:

To use gaseous fuels in a CI engine, fuel supply, combustion system, ignition, and controls must be modified. The level of modification depends on whether dual-fuel or spark-ignition conversion is chosen. With proper engineering, CI engines can efficiently run on gaseous fuels, offering cost and environmental benefits.