Every spark decides the output
Gas engine performance depends on more than delivering a spark. Ignition timing and spark duration must suit the engine, while the air/fuel ratio must remain appropriate as load and fuel quality change. Gill GS8, GS12 and GT6 ignition modules control the spark. The AF120 adds closed-loop air/fuel ratio control for spark-ignited gaseous-fuel engines.
How do ignition and air/fuel ratio control affect a gas engine?
On a spark-ignited gas engine, ignition timing decides when combustion starts, spark duration affects the energy available to start it, and air/fuel ratio control manages the mixture the engine receives. Together they govern combustion stability, output and fuel use. Gill ignition modules control the spark, and the AF120 controls the mixture using oxygen sensor feedback.
Gas engines used in generators, combined heat and power (CHP) systems and compressors may operate for thousands of hours each year, often with limited operator intervention. Consistent operation depends on controlling combustion as operating conditions change.
Ignition timing determines when combustion starts. Spark duration influences the energy available to initiate combustion, while air/fuel ratio control manages the mixture supplied to the engine. Together, these factors affect combustion stability, engine output and fuel use.
Poorly matched settings can contribute to misfire, rough running, reduced output and increased maintenance requirements. The appropriate control system depends on the engine design, cylinder count, fuel characteristics and operating conditions.
What the control system needs to manage
Gas engine controls operate in demanding conditions, often mounted on or close to equipment exposed to heat, vibration and moisture. The control system must also match the engine’s configuration and wider fuel and ignition systems.
Cylinder count and firing pattern
Ignition control must match the number of cylinders and the engine’s firing pattern. Gill offers the GS8 for engines with up to eight cylinders, the GS12 for engines with up to 12 cylinders, and the GT6 for smaller engines with one to six cylinders.
Spark duration
Spark duration is one of the parameters configured for the engine. The GS12 supports spark durations of up to 3,000 microseconds, while the GT6 supports up to 1,500 microseconds. The appropriate setting depends on the engine and its operating requirements.
Closed-loop air/fuel ratio control
The AF120 uses a Bosch UEGO wideband oxygen sensor to monitor the exhaust and support closed-loop adjustment of the air/fuel ratio. This allows the control system to respond to changing operating conditions, subject to the capabilities of the complete engine and fuel system.
Environmental protection
Engine-mounted controls must withstand the environment in which they operate. Gill specifies IP67 protection across the range. Installation conditions and the requirements of the complete system should still be checked during specification.
Ignition control or ignition plus mixture control?
The choice depends on how much control the engine needs over combustion and how much its operating conditions vary.
| Consideration | Basic or legacy ignition |  Digital ignition: GS8, GS12 or GT6 |  Ignition plus AF120 |
|---|---|---|---|
| Ignition timing | Limited adjustment | Configured and mapped in software | Configured and mapped in software |
| Air/fuel ratio | Separate or manual control | Separate from ignition module | Closed-loop control using an exhaust oxygen sensor |
| Communication | May have no communications interface | CAN | CAN, with AF120 also supporting 4 to 20 mA and RS232 |
| Typical application | Simpler engines with relatively stable operating conditions | Engines requiring configurable digital ignition | Engines requiring ignition control alongside closed-loop mixture control |
Ignition and mixture control perform different jobs. The ignition module manages the spark; the AF120 controls the air/fuel ratio. They can be specified together where the engine and application require both functions.
System requirements and specification
Engine configuration
The GT6 supports one to six cylinders on engines up to 13 litres. The GS8 supports up to eight cylinders and the GS12 up to 12 cylinders. Confirm the specific engine configuration and compatibility before selecting a module.
Control requirements
An ignition module controls ignition functions; it does not replace the engine’s sensors, actuators or wider management system. Determine which functions are already provided by the engine controller and whether independent air/fuel ratio control is required.
Fuel-system compatibility
The AF120 drives stepper or current-controlled bypass valves. The valve arrangement and fuel system must be compatible with the selected controller and intended control strategy.
Mapping and commissioning
Ignition maps are configured in Gill software for the individual engine application. Allow time for configuration, integration and commissioning as part of the project plan.
Gill products for gas engine control
Gill offers three ignition modules and an air/fuel ratio controller. The appropriate combination depends on the engine specification and the control functions required.
GS8 and GS12
Digital gas engine ignition modules
The GS8 and GS12 provide configurable ignition control for engines with up to eight or 12 cylinders respectively.
GT6
Compact ignition module
The GT6 is designed for smaller gas engines, including generator sets and compressors.
AF120
Closed-loop air/fuel ratio controller
The AF120 controls the air/fuel ratio in spark-ignited gaseous-fuel engines using feedback from a Bosch UEGO sensor.
insight
How ignition and air/fuel ratio control work together
In a spark-ignited gas engine, ignition timing determines when the spark initiates combustion, while the air/fuel ratio influences how the mixture burns. These variables interact, so the control strategy needs to account for both.
A closed-loop air/fuel ratio controller uses a wideband oxygen sensor in the exhaust to monitor the combustion result and adjust the mixture towards its target. The ignition module applies the timing and spark-duration settings configured for the engine.
When both functions are required, the ignition module and air/fuel ratio controller work as complementary parts of the wider engine management system. Their integration, calibration and commissioning must be appropriate to the engine and fuel system.
Related applications and resources
ApplicationGas engines and combined heat and power
Ignition and control considerations for gas engines in CHP installations.
KnowledgeHow a four-stroke engine works
Understand the combustion cycle that ignition control acts on.
Product rangeGas engine controls
Explore the wider range of Gill ignition and mixture-control products.
IndustryIndustrial process
Explore measurement and control applications across engines, drives and process plant.
Speak to our team
Tell us what you need to measure, where and under what conditions. We’ll help you work out the appropriate approach.
Frequently asked questions
A gas engine ignition module controls when the spark occurs and manages ignition parameters such as spark duration according to the engine’s configured settings. The module must be suitable for the engine’s cylinder count and firing pattern.
An air/fuel ratio controller regulates the mixture supplied to a spark-ignited engine. The Gill AF120 uses feedback from a Bosch UEGO wideband oxygen sensor in the exhaust to support closed-loop mixture control as operating conditions change.
The choice depends primarily on cylinder count, engine displacement and the application. The GT6 covers one to six cylinders on engines up to 13 litres; the GS8 supports up to eight cylinders, and the GS12 supports up to 12. Confirm compatibility with the specific engine before selecting a module.
Not every engine requires both products. An ignition module manages the spark, while an air/fuel ratio controller regulates the mixture. Whether closed-loop mixture control is needed depends on the engine design, fuel system, operating conditions and overall control strategy.
CAN communication is specified for the ignition modules. The AF120 also supports 4 to 20 mA and RS232. Confirm the available interfaces and any additional requirements against the relevant product datasheet and the wider engine-control architecture.
Gill specifies IP67 protection across the range. Suitability for a particular installation also depends on operating temperature, vibration, mounting, wiring and other environmental conditions. Check the individual product specifications against the intended installation.