Troubleshooting Biogas Gensets: Common Problems, Causes & Practical Solutions

Many biogas plants are designed around familiar diesel-generator thinking. The assumption is simple: if a diesel genset runs smoothly, a biogas genset should behave similarly. In practice, biogas fuel is more variable—its quality depends on feedstock, digestion, gas cleaning and daily operating habits. That means troubleshooting a biogas genset is always a combination of:

• Engine-side checks (spark plugs, ignition, lubrication, cooling).
• Gas-side checks (pressure, methane percentage, H₂S, moisture).
• Electrical-side checks (load, voltage, frequency, protection relays).

This guide is structured according to real-world symptoms that operators typically see on site. For each symptom, we outline likely causes and give practical checks and actions. It is not a replacement for engine manuals or experienced service technicians, but it can make your troubleshooting faster and more systematic.

Note: Always follow OEM safety instructions and lockout/tagout procedures before working on electrical and mechanical systems.

A non-starting genset is one of the most frustrating issues for plant operators. It usually points to problems in three areas: gas supply, ignition or safety interlocks.

Step-by-Step Checks

• Gas Pressure: Verify that gas pressure at the engine inlet is within the recommended range. Too low or too high pressure can prevent starting.
• Gas Quality: Check if the digester is producing stable biogas. Very low methane percentage or excessive CO₂ can make ignition difficult.
• Ignition System: Confirm that spark plugs, ignition coils and leads are in good condition and properly connected.
• Safety and Sensors: Look for any active alarms—low lube oil pressure, high temperature, gas leak or emergency stop switches.
• Battery and Starter: Ensure the battery voltage is adequate and the starter motor is functioning normally.

If the engine cranks but does not fire, it is often a fuel–spark–timing issue. If the engine does not crank at all, focus first on electrical and safety circuits.

Misfiring and unstable speed (hunting) indicate that the engine is not receiving a consistent combustible mixture. Left unresolved, this can damage the engine and alternator over time.

Likely Causes

• Biogas flow fluctuating due to inconsistent digester pressure or blower issues.
• Moisture or condensate entering the gas line and reaching the mixer.
• Clogged gas filters or partially blocked gas valves.
• Weak spark on one or more cylinders (worn plugs, damaged leads).
• Incorrect air–fuel ratio adjustment or faulty mixer/venturi.

Practical Checks and Fixes

• Drain all condensate traps and low points in the gas pipeline.
• Inspect and clean gas filters, strainers and valves as per maintenance schedule.
• Check spark plugs for deposits; clean or replace if necessary and verify the gap.
• Verify that air–gas mixture settings match the OEM recommendations for current gas quality.
• Monitor digester gas pressure for sudden fluctuations and rectify any blower or pressure-regulation issues.

On sites where biogas production varies significantly during the day, it may be necessary to coordinate engine loading and operating hours with gas availability.

Operators often notice that the genset no longer delivers its rated kilowatt output, even though it starts and runs. This usually points to gas calorific value, air–fuel ratio or engine-health issues.

Key Diagnostics

• Check Methane Percentage: A drop in CH₄ content reduces the energy available per cubic metre of gas.
• Review Air Filters: Clogged air filters restrict combustion air and reduce effective power.
• Inspect Turbocharger / Intake (if applicable): Deposits or leaks can reduce boost pressure.
• Assess Engine Wear: Low compression due to worn rings or valves can reduce power over time.
• Confirm Load Measurement: Ensure that the connected load and measurement instruments are accurate.

In many cases, performance improves significantly when gas quality is stabilised through better digestion control and when basic maintenance (filters, plugs, oil) is updated according to run hours.

Knocking (metallic pinging) and excessively high exhaust temperatures are serious warning signs. They can lead to piston, valve and head damage if ignored.

Possible Reasons

• Over-advanced ignition timing relative to the gas quality.
• Lean air–fuel mixture causing high combustion temperatures.
• Insufficient cooling-water flow or blocked radiator fins.
• Deposits in combustion chamber raising compression ratio locally.
• Sustained operation at or above rated load in high ambient temperatures.

Recommended Actions

• Immediately reduce load if knocking is observed and investigate before resuming full load.
• Review ignition timing with reference to engine manufacturer guidelines for biogas operation.
• Ensure cooling system is functioning—check coolant level, pump, belts and radiator cleanliness.
• Inspect for carbon deposits during scheduled overhauls and clean as per OEM procedure.

As a general rule, persistent knocking should never be accepted as “normal”. It always indicates that something in the fuel–timing–load combination is incorrect for that engine.

Biogas is not a clean “ready-to-use” fuel when it leaves the digester. Hydrogen sulphide (H₂S), moisture and particulate matter must be managed properly. Otherwise, long-term damage occurs in the engine and gas lines.

Warning Signs

• Unusual corrosion on engine parts, valves, turbocharger or exhaust.
• Frequent spark plug fouling or deposits on valves and piston crown.
• Strong sulphur smell even after gas-cleaning stages.
• Condensate with strong odour or visible particulate matter in condensate pots.

Gas Cleaning and Preventive Measures

• Use appropriately sized H₂S scrubbers (iron media, biological or chemical) and maintain them as per schedule.
• Provide adequate moisture separation through condensate traps and knock-out drums, especially before the genset.
• Monitor H₂S levels at regular intervals and replace or regenerate media on time.
• Ensure gas piping is sloped correctly so that condensate does not collect in dead legs.

For many biogas power projects, consistent gas cleaning is the single biggest factor that determines engine life and maintenance cost over the years.

Even if the engine is running well, electrical issues can cause frequent tripping or unstable power quality. This affects connected loads and reduces confidence in the system.

Areas to Check

• Load Variations: Large motors, compressors or pumps starting and stopping suddenly can cause dips and spikes.
• Governor / Speed Control: If the speed controller is not tuned, frequency can drift under changing loads.
• Protection Settings: Overly sensitive settings on under-voltage, under-frequency or reverse power relays.
• Cable and Earthing: Poor connections, undersized cables or weak earthing arrangements.

It is important to coordinate electrical design—cables, switchgear, protection and synchronisation (if grid-connected)—with the genset capacity and the nature of connected loads. Periodic testing and logging of voltage, current and frequency help identify patterns in tripping incidents.

Many troubleshooting calls can be avoided if a simple preventive maintenance schedule is followed consistently. Below is a generic checklist that can be adapted to your engine model and site conditions.

Routine issues such as filter cleaning, condensate draining and basic electrical checks can be handled by in-house teams. However, there are situations where it is safer and more economical to involve the engine OEM or an experienced biogas-genset partner.

• Repeated major failures (piston, valves, crankshaft) within short operating hours.
• Persistent knocking or high exhaust temperature despite basic corrections.
• Chronic low power that cannot be explained by gas-quality variations alone.
• Plans to increase plant capacity or integrate additional loads.

In some cases, performance and reliability improve dramatically when the biogas plant is paired with a better gas-cleaning system or when the engine is specifically configured for biogas rather than converted from diesel. Partners like Enersol Biopower can help evaluate whether retrofits, new-biomass gasifiers or improved biogas utilisation strategies will offer a better long-term outcome.

A biogas genset is more than just an engine; it sits at the heart of an integrated system—digester, gas cleaning, fuel handling, cooling and electrical distribution. Effective troubleshooting therefore requires a systems view. When operators use a structured approach to symptoms, causes and actions, downtime reduces, maintenance becomes predictable and the business case for biogas power strengthens.

By paying close attention to gas quality, following preventive maintenance schedules and taking timely advice from experienced engine and biogas partners, plant owners can enjoy years of reliable power from their biogas assets. Troubleshooting then becomes a learning tool, not a constant firefighting exercise.

As a biogas genset and biomass gasifier solution partner from India, Enersol Biopower works with dairies, gaushalas, food-processing units, STPs and industrial clients to design, commission and support biogas-based power plants that are both technically sound and practically maintainable on the ground.