A GAS GENERATOR IS NOT A DIESEL GENERATOR WITH A DIFFERENT FUEL TANK.
A purpose-designed gas generator is an integrated combustion and electrical-power system engineered around a defined gaseous fuel.
Its performance depends on the relationship between:
GAS QUALITY → GAS PRESSURE & FLOW → ENGINE → CONTROLS → ALTERNATOR → LOAD → HEAT REJECTION → EXHAUST → EMISSIONS → POWER-SYSTEM INTEGRATION
This makes gas-generation engineering fundamentally different from simply asking:
“What kVA gas generator do I need?”
The correct question is:
What electrical duty must be served, what gaseous fuel is actually available, what engine-generator configuration is compatible with that fuel, and can the complete system deliver the required resilience and lifecycle performance?
1. Purpose-built gas generation vs dual-fuel conversion
These must remain clearly separated.
The engine and controls are engineered around the applicable gaseous fuel architecture.
Diesel + gas dual fuel
An existing/eligible diesel combustion architecture retains diesel while adding an approved gaseous-fuel contribution.
Gas Generator ≠ Dual Fuel Diesel Generator
Dual-Fuel Conversion for Diesel Generator Sets through Dual-Fuel Performance, Load Behaviour & Gas Substitution Engineering already cover dual-fuel conversion in depth. Gas Generator Systems concentrates on purpose-designed gas generation.
2. Define the fuel before selecting the generator
“Gas generator” is incomplete terminology.
The project should establish the actual fuel:
pipeline natural gas / PNG • biogas • biomethane / renewable natural gas where applicable • associated or field gas • other manufacturer-approved gaseous fuel.
Different fuels can have materially different:
composition • heating value • methane number/knock characteristics where applicable • contaminants • moisture • pressure.
Therefore equipment selection begins with a fuel specification, not merely a fuel name.
3. Gas composition matters
Obtain the available fuel specification where required.
Potentially relevant constituents include:
methane • heavier hydrocarbons • carbon dioxide • nitrogen • hydrogen sulphide/other contaminants where applicable • moisture.
The engine manufacturer defines the acceptable fuel envelope.
Do not assume that a generator designed for one pipeline-gas specification can automatically operate on untreated biogas or field gas.
Fuel energy input can be expressed conceptually as:
Q̇_fuel = ṁ_fuel × LHV
Q̇_fuel = fuel-energy rate
ṁ_fuel = fuel mass-flow rate
LHV = lower heating value
Volume-based calculations can also be used with the appropriate gas reference conditions.
The important principle is:
Generator fuel demand is an energy requirement—not simply a cubic-metres-per-hour number copied between projects.
5. Gas reference conditions
Gas volume changes with:
Therefore gas-flow figures should identify the relevant:
when technical accuracy requires them.
Do not compare two volumetric gas-consumption figures unless their measurement basis is compatible.
6. Gas quality can affect available engine output
If fuel characteristics differ from the engine’s reference fuel, available output or permissible operating conditions may change.
Verify the actual manufacturer data for:
fuel quality • ambient temperature • altitude • cooling arrangement • rating.
Do not assume nameplate electrical output remains unchanged under every fuel condition.
7. Establish the electrical load
continuous kW • kVA • PF • largest motor • motor starting • UPS/nonlinear loads • transformers • future load • simultaneous operation.
Gas fuel does not remove the fundamentals of generator sizing.
8. kW and kVA
Where power factor is applicable:
kVA = (kW) / (PF)
But sizing must also consider:
transient response • starting loads • alternator capability • engine response • ambient derating • redundancy.
Do not simply divide facility kW by 0.8 and call the generator selected.
9. Gas-engine transient response
A gas engine can have different transient characteristics from a comparable diesel engine.
This becomes important for:
large motors • compressors • chillers • elevators • UPS systems • sudden process loads.
Review manufacturer transient-performance data for the actual generator.
A generator that supports the steady-state kW may still require different sizing because of the site’s load steps.
For each significant motor establish:
rated kW • starting method • starting current/kVA • acceleration time • sequence • acceptable voltage/frequency disturbance.
Possible starting methods include:
direct-on-line • star-delta • soft starter • VFD
depending on the application.
Do not assume gas generation cannot start motors; equally, do not assume diesel-generator sizing rules transfer unchanged without checking the actual engine-generator response.
For UPS-backed facilities determine:
UPS topology • rectifier behaviour • battery-recharge demand • input PF • harmonic characteristics • step loading.
The generator and UPS should be assessed as an integrated source/load system.
Gas-generator selection for data-centre or critical-power duty therefore requires more than kVA matching.
12. Standby vs prime operation
A gas generator may be evaluated for:
standby • prime • continuous/base-load • CHP/cogeneration • hybrid/microgrid duty.
The applicable rating must come from the manufacturer for the actual engine-generator configuration.
Do not transfer diesel terminology or rating assumptions blindly.
13. Pipeline gas for standby power
Pipeline gas can reduce dependence on on-site liquid-fuel storage.
But critical-power engineering must ask:
Will the gas network remain available during the same emergency that removes electrical utility power?
This depends on the local infrastructure and event.
Pipeline availability should therefore be treated as a resilience dependency, not an automatic advantage.
14. Fuel autonomy changes meaning
With a diesel tank, autonomy is largely an on-site stored-energy problem.
With pipeline gas, the site may not have a finite on-site fuel inventory.
supply continuity • upstream pressure • contractual conditions • regulator dependency • external infrastructure.
The resilience model changes.
The selected generator requires fuel within a defined inlet-pressure envelope.
source pressure • minimum dynamic pressure • maximum pressure • regulator arrangement • pressure variation.
Use actual manufacturer requirements.
No universal gas-pressure number should be published.
The site must supply the generator’s maximum required fuel flow while accounting for other simultaneous consumers.
Raw biogas can differ significantly from pipeline natural gas.
Depending on source, it can contain varying:
methane • CO₂ • moisture • hydrogen sulphide • siloxanes/other contaminants.
A generator designed for treated natural gas should not automatically be fed untreated biogas.
Fuel treatment may become a major part of the plant.
Depending on engine and raw-gas quality, treatment can involve control of:
moisture • particulates • corrosive contaminants • siloxanes or other compounds.
Actual allowable limits come from the engine manufacturer.
Do not assume one universal gas-cleanliness specification.
16. Biomethane / renewable natural gas
Upgraded biogas can potentially approach natural-gas quality, depending on the processing and specification.
But generator compatibility still requires:
actual fuel composition • pressure • heating value • manufacturer limits.
The word biomethane does not replace a fuel analysis.
17. Wastewater and landfill-gas applications
These applications can create an attractive relationship between:
waste stream → fuel → generation
but also introduce challenges such as:
fuel variability • contaminants • treatment • engine maintenance • corrosion.
A successful project is often as much a fuel-treatment project as a generator project.
Agricultural or anaerobic-digestion projects should establish:
gas-production profile • methane concentration • storage/buffer capacity • treatment • generator demand • parasitic loads.
Do not size the generator solely from digester peak gas production.
available usable gas energy ↔ electrical/thermal demand.
Direct answer
Biogas Generators should be evaluated from the actual operating requirement, load profile, source and distribution architecture, protection, controls, site conditions and continuity consequences. Equipment-specific limits, regulatory applicability and project-specific design decisions must be verified before procurement or operation.