In short. Bi-fuel sets can run on either of two fuels, often gas or a liquid fuel, with controls that switch between them. They differ from dual-fuel sets, which burn diesel and gas together. Switching logic, safety and fuel logistics decide success.
Bi-fuel versus dual fuel
| Feature | Bi-fuel | Dual fuel |
|---|---|---|
| Fuel use | One fuel at a time | Diesel pilot plus gas together |
| Switching | Planned or on failure | Ratio managed continuously |
| Typical use | Fuel flexibility | Diesel replacement |
See dual-fuel engineering for comparison.
Design points
- Switching logic: automatic on supply loss, manual by operator, or by price.
- Output on each fuel; derating on the alternate.
- Transitions: does power stay continuous?
- Storage and handling for both fuels.
- Safety, detection and purge.
- Maintenance for two fuel systems.
Why use it
- Resilience against single-fuel disruption.
- Access to cheaper fuel at times.
- Step towards lower-carbon fuels.
Alternative fuels
Renewable diesel, biodiesel blends and other fuels need engine and storage compatibility checks. See HVO readiness and cleaner-fuel systems.
Illustrative example
A remote site with gas bottles and diesel uses bi-fuel so that a delayed gas delivery does not stop the plant: the set switches to diesel and logs the event. The test of that switch was done before approval.
Operating modes in a bi-fuel system
| Mode | Description |
|---|---|
| Primary fuel | Runs on the preferred fuel, such as gas |
| Automatic fallback | Switches to the alternate if primary pressure or quality fails |
| Manual selection | Operator chooses by price or availability |
| Dual-fuel mix | Only in systems designed for blending |
Switching without a break in supply
Whether the set can change fuel while carrying load depends on the design. Some change over in seconds with a brief power dip; others require reducing load. Establish this early and plan for critical loads, for example with a UPS or storage to bridge the change. Test it in commissioning.
Rating on each fuel
Output on gas can be lower than on diesel. Size for the lower rating if the load must be carried on either fuel. Check ratings at your site temperature and altitude.
Storage and logistics
- Size liquid fuel storage for the autonomy required.
- Size gas storage for the same, or accept diesel as the long-duration fuel.
- Rotate stocks.
- Maintain both fuel trains.
Control and alarms
- Clear indication of which fuel is in use.
- Alarms for gas pressure and diesel level.
- Logging of fuel switching events.
Emerging alternative fuels
Engines may be approved for blends or newer fuels. Before using any, obtain the maker’s written approval, test a sample, and update maintenance routines. See HVO readiness.
When bi-fuel makes sense
It suits sites that value fuel flexibility, for example where gas is cheaper but supply may be interrupted, and where reliability of power outweighs the complexity of two fuel systems.
The master engineering question
When the preferred fuel fails, how fast and how safely does the set move to the other?
What to send us
Send site fuels and duty. Send your application details.
Questions engineers ask
Does output drop on gas?
Often; check the rating on each fuel.
Is switching on load possible?
Depends on design; test.
Is bi-fuel the same as dual fuel?
No.
Is maintenance doubled?
Both fuel systems need care.
General guidance only. Use maker data.