In short. RECD targets exhaust pollutants on the existing engine. Dual fuel changes the fuel and part of the combustion. Replacement gives a new engine under current rules. Duty profile, engine condition, fuel access and regulation decide which is best.
Comparison
| Criterion | RECD | Dual fuel | Replacement |
|---|---|---|---|
| Main benefit | Lower exhaust pollutants | Lower diesel use, possible emission change | Modern engine and compliance |
| Best for | Sound engines, steady or loaded duty | High run-hours, gas available | Old, worn or non-compliant sets |
| Limitations | Temperature, back-pressure, maintenance | Gas supply, safety, load limits | Capital cost, downtime |
| Approval | Confirm route | Confirm route | Standard for new sets |
See each: RECD, dual fuel, replacement decision.
Decision logic
- What does the rule require for this set and place?
- What is the engine’s condition and remaining life?
- How many hours per year, and at what load?
- Is gas available and reliable?
- What is the total cost over the remaining life?
Typical outcomes (illustrative)
- Healthy standby set, few hours: RECD or just compliance documentation.
- Prime set, steady load, pipeline gas: dual fuel.
- Old set, high oil consumption, high hours: replace.
Illustrative example
A school has a 15-year-old set used 80 hours a year. Replacement is costly for such low use; a retrofit or restricted operation may be enough, subject to local rules. A factory with 4,000 hours a year looks at dual fuel or replacement instead.
Illustrative scenarios
| Scenario | Likely best route | Why |
|---|---|---|
| Hospital standby set, 60 hours a year, sound engine | RECD or documented restricted use; consider storage | Few hours make fuel savings small |
| Factory prime power, 5,000 hours a year, gas pipeline nearby | Dual fuel or gas set | Fuel savings accumulate |
| Twenty-year-old set, heavy oil use, frequent repairs | Replacement | Poor base for investment |
| Data centre with strict uptime, rules tightening | New compliant sets plus storage | Reliability and compliance together |
A lifetime cost sketch
Lifetime cost = capital + installation + consumables + fuel + maintenance + downtime risk − residual value
Fill each term over the same remaining life for each option. Fuel dominates for high-hours duty; capital and compliance dominate for standby.
Risks to weigh
- RECD: device performance on an old engine, back-pressure, maintenance discipline.
- Dual fuel: gas supply reliability, safety, transient response.
- Replacement: capital, downtime, delivery lead time.
- All: rule changes, approvals.
Hybrid answers
Options can combine: a new compliant set plus storage; a retrofit now with replacement planned in a few years; dual fuel on the busiest set and documentation only on the standby sets. See hybrid modernisation.
Making the decision traceable
- State the objective: compliance, cost, reliability, carbon.
- List the options and the data behind each.
- Score and discuss.
- Record the decision and review date.
This record helps if rules change later or if the decision is questioned.
The master engineering question
Which option meets the rule at the lowest lifetime cost and risk for this duty?
What to send us
Send engine, hours, location and fuel options. Send your application details.
Questions engineers ask
Which is cheapest?
Depends on duty and life; calculate for the case.
Can I combine options?
Sometimes, subject to engineering and approvals.
What if rules change?
Choose with some flexibility.
Who decides compliance?
The relevant authority.
General guidance only. Confirm regulations.