In short. Dual-fuel engineering balances diesel pilot, gas quantity and air supply so combustion stays stable across loads. The controller watches gas pressure and quality and falls back to diesel when limits are reached.
Physics to control
Gas-air mixture in the cylinder → diesel pilot ignites → flame spreads → power. Too much gas at low load can cause misfire; too much at high load can cause knock. The controller sets the safe ratio for each load.
| Element | Role |
|---|---|
| Gas train | Pressure regulation, filtering, shutoff valves |
| Gas injection or mixer | Admits gas into intake air |
| Dual-fuel controller | Manages ratio and fallback |
| Sensors | Gas pressure, exhaust temperature, knock, speed, load |
Gas quality
Methane content, calorific value and contaminants vary, especially for biogas. Quality changes combustion behaviour and may need gas conditioning or lower substitution.
System effects
- Load step response can differ from diesel. See transient response.
- Governor and AVR may need re-tuning.
- Fallback to diesel causes a change in the engine’s dynamic behaviour.
Protection and safety
- Gas leak detection and ventilation.
- Automatic gas shutoff on engine trip or gas fault.
- Safe purge and restart procedures.
See also conversion overview and compatibility.
Illustrative example
At 30 percent load the set is held at a lower gas share to avoid misfire. At 70 percent load a higher share is allowed. A drop in gas pressure triggers a smooth return to diesel, which the test confirms.
Gas admission methods
| Method | Description | Consideration |
|---|---|---|
| Central mixer | Gas mixed with air before the intake manifold | Simpler; slower response to load changes |
| Port injection | Gas injected near each intake port | Better control per cylinder; more parts |
Why exhaust temperature and knock sensing matter
Exhaust temperature per cylinder shows whether combustion is balanced. Rising temperature at one cylinder may signal excess gas or a faulty injector. Knock sensors detect abnormal combustion early. The controller uses these signals to reduce gas before engine damage occurs. Check that these sensors are included in the conversion and that alarm levels are set.
Gas train design
- Isolation valve at the entry.
- Filter or strainer.
- Pressure regulation to the engine requirement.
- Double block and bleed or equivalent safety shutoff arrangement.
- Flame arrestor or non-return device where applicable.
- Pressure switches and gauges.
Gas composition
Natural gas, Bio-CNG and biogas differ in methane content and in heating value. Biogas often contains hydrogen sulphide and moisture that attack engine parts; it needs cleaning and drying. The controller’s gas map must match the gas actually supplied.
Transient response
With a gas-air mixture in the manifold, load response can be slower than diesel-only. Plan load steps, for example by sequencing large loads, and test. If the facility has large step loads, a dual-fuel set may need more diesel share, battery support or a larger set. See frequency dip.
Testing before acceptance
- Load steps at several gas shares.
- Gas-loss fallback on load.
- Emergency stop with gas valves closing.
- Exhaust emissions measurement where required.
The master engineering question
At each load and gas condition, what keeps the combustion stable and what happens when the gas disappears?
What to send us
Send engine data and gas analysis. Send your application details.
Questions engineers ask
Why does low load limit gas?
Lean mixtures burn poorly.
Does gas quality matter?
Yes, composition changes combustion.
Is fallback instant?
Designed to be quick; test it under load.
Does the alternator change?
No, but dynamic response can.
General guidance only. Follow conversion maker procedures.