In short. In a dual-fuel set diesel still ignites the charge, while natural gas, biogas, Bio-CNG or LPG supplies part of the energy. If gas pressure or quality drops, the controller returns to full diesel. The share of diesel replaced varies with engine, load and gas supply.
How it works
Gas admitted with intake air → diesel pilot injection ignites the mixture → controller manages the diesel and gas ratio → fallback to diesel if gas is lost.
Why consider it
- Reduced diesel consumption where gas is cheaper or available.
- Potential emission benefits, to be verified for the engine.
- Diesel remains as a backup fuel.
Limits
| Limit | Detail |
|---|---|
| Substitution rate | Varies; low loads often allow less |
| Engine suitability | Model and condition matter |
| Gas infrastructure | Supply, pressure, storage and safety |
| Load response | Check step-load behaviour |
| Approvals | Confirm local requirements |
Read more: diesel plus gas engineering, compatibility assessment and performance and substitution.
Safety
Gas introduces leak and ventilation hazards: detection, shutoff valves, hazardous-area review and trained staff are essential.
Illustrative example
A factory with a gas pipeline near its generator house runs a prime-duty set at steady load. Dual fuel suits that profile. A hospital standby set with rare runs gets little benefit and may prefer another route.
Energy substitution in simple terms
Substitution is the share of the fuel’s energy provided by gas instead of diesel.
Substitution (%) = Gas energy ÷ (Gas energy + Diesel energy) × 100
Published figures for dual-fuel systems span a wide range, and the best values apply to steady, moderately to highly loaded operation. On a real load profile the weighted figure is lower. Plan the economics on a conservative number supported by a trial or maker data for your engine.
Fuel economics
| Input | Why it matters |
|---|---|
| Diesel price per litre | Savings base |
| Gas price per unit energy | Offsetting cost |
| Annual generation hours | Scale of savings |
| Average load | Achievable substitution |
| Conversion and installation cost | Payback |
| Added maintenance | Reduces net savings |
Do the calculation at a few gas and diesel price scenarios, because these prices move.
Safety essentials
- Gas detection with alarms and automatic shutoff.
- Ventilation of the generator room.
- Hazardous-area assessment for electrical equipment near gas parts.
- Purging and leak testing procedures.
- Training for operators and maintenance staff.
- Emergency procedures posted.
Controls behaviour to verify
- Smooth start on diesel, then gas admission after stable running.
- Reduction of gas at light load.
- Instant fallback to diesel on gas loss.
- Safe shutdown with gas valves closed.
Standby sets
For a standby set that runs a few hours a year, the savings are small and the added complexity may be a liability. Dual fuel is generally more attractive for prime or long-hours duty. Assess your own duty before spending on conversion.
The master engineering question
Does the duty profile run long enough, at enough load, with reliable gas, to justify conversion?
What to send us
Send engine data, duty and gas availability. Send your application details.
Questions engineers ask
Can any diesel set be converted?
No; assess the engine first.
What if gas runs out?
The controller falls back to diesel.
Which gases?
Natural gas, biogas, Bio-CNG and LPG are commonly considered, subject to quality.
Is it safe?
With proper design, detection and training.
General guidance only. Substitution rates vary; verify per engine.