Electronic controls in genset engines
To understand how electronics have simplified maintenance of industrial engine generator sets, one only needs to look inside the garage at home.
The new car parked there does not need twice-annual tune-ups. It probably doesn’t need new spark plugs until the odometer hits 100,000 miles. On the whole, it needs minimal maintenance — yet it is far more reliable, more fuel efficient, quieter, smoother running, and cleaner than cars built 20 or 30 yr ago.
The same is true, on a larger scale, of the natural-gas-fueled reciprocating engines that today drive generator sets in distributed generation, standby, peak-shaving, combined heat and power (CHP), and other applications.
Electronic engine control helps owners of generation systems comply with ever-stricter emissions limits, drive down operating costs, and save on maintenance. Perhaps most important, it helps liberate staff from babysitting equipment, allowing more focus on strategic issues that drive competitiveness and profitability.
Modern engine electrical and electronic systems require very little maintenance. Obviously, that has not always been true. Engine electrical systems, as recently as the 1980s, were relatively high-maintenance items. The key electrical system was and still is the ignition system. Correct ignition timing is critical to engine performance, emissions control, fuel efficiency, and longevity.
Until the 1990s, ignition timing depended on magnetos, which are essentially miniature generators driven off engine gearing that produce electrical pulses and generate the spark that ignites the fuel in the cylinders.
Magnetos — with bearings, windings, breaker points, seals and other components subject to wear and degradation — required regular maintenance and periodic rebuilding. Plus, even in their latest solid-state versions, magnetos were inherently limited to timing accuracy of about
Timing accuracy became ever more important as manufacturers began increasing the power limits of generator sets that offered users continuous maximum output for better return on investment (ROI). Under these higher output conditions, detonation (knocking) in the cylinders became a major concern. Engine manufacturers developed electronic systems to sense detonation and automatically retard the timing to compensate, but it was difficult to integrate the technology with magneto-based ignition systems.
Ignition also became more critical as manufacturers developed even leaner-burning engines with higher operating output to maximize fuel economy and limit exhaust emissions — especially oxides of nitrogen (NO x ).
The age of electronics
Electronic engine controls began arriving in the early 1990s and, along with computer technology in general, they grew exponentially in power and performance. The first electronic ignition systems were environmentally sealed inside housings with no wearing parts. They delivered timing accurate to within
A timing sensor monitors a reference point on the cam gear and indexes off one cylinder. By detecting the location of the reference point, the system knows the precise position of each piston in the combustion cycle and produces the spark with the optimum timing.
An added feature is detonation-sensitive timing integrated with the ignition control module. In this system, an accelerometer mounted on the engine block (in some cases one per bank of cylinders on V engines) detects vibration caused by detonation and sends a signal to a processor, which instructs the control to retard the timing until the detonation is eliminated.
Later, manufacturers developed electronic air-fuel ratio controls to regulate the fuel mix in the cylinders. These systems help significantly to keep engines operating in the “sweet spot” of optimum fuel economy, power, and emissions control. They also save operators time by eliminating manual adjustments. The operator programs the unit to achieve the desired NO x output, power, and efficiency level for the user’s site conditions, and the control maintains the air-fuel ratio within the necessary range.
The challenge of these air-fuel ratio controls is that they rely on a feedback loop. Some control systems measure the oxygen content, which dictates adjustments to fuel and air flow. Exhaust oxygen is measured by a sensor in the exhaust stream — a hostile environment. These sensors require inspection, calibration, and periodic replacement. The exact maintenance regimen and frequency depends on the fuel, engine model, and the application. For example, sensors on engine-generators burning landfill gas need attention more frequently. In addition, because both humidity and ambient temperature affect the air-fuel ratio, a truly effective oxygen feedback control system should be integrated with a humidity sensor, or “weather station,” that detects changes in those conditions so that the system can adjust for them as well.
Those issues aside, earlier-vintage electronic controls remain appropriate for certain applications, especially where air-quality regulations are not extremely strict and where long-term fuel and other operating costs are not critical drivers of ROI. Such applications can include peak shaving or distributed generation systems involving relatively short annual running hours.
Quantum leap forward
As distributed generation gained favor, the market demanded substantially higher performance and efficiency from natural-gas-fueled generator sets. At the same time, stricter air regulations forced manufacturers to drive down NO x and other emissions.
Advanced electronic control systems made those improvements possible, while also making engine monitoring, operations, and maintenance simpler than ever. While early engine controls were to a large extent actuators being controlled by multiple interfacing modules, latest-generation controls are moving to smart actuators and one module that is the brain power of all the engine systems, providing truly intelligent control. Newer actuators not only respond to control inputs and provide position feedback signals, but also provide flow, temperature, and pressure data for performance mapping purposes.
With sophisticated electronic control, generator sets can achieve mechanical efficiencies up to 43.5% while producing NO x at less than 1.0 g/bhp-hr. These engines are designed — and well suited — for distributed generation, CHP, and other applications where ROI depends on the maximum power density or minimum long-term electricity cost per kWh.
The latest control systems integrate multiple sensors measuring intake air pressure and temperature, exhaust temperature, detonation, electric power output, speed, timing, and other variables. In addition to a central control microprocessor, the engine may have a temperature-sensing control module, smart fuel valve, and smart throttle that feed data back to the central control.
This single control then regulates all critical functions — start-stop logic, ignition, air-fuel ratio, and governing — to keep the engine operating according to parameters prescribed for the application. The system is built around factory-programmed, application-specific operating maps and complex algorithms. The engine responds quickly and precisely and remains under tight control and in safe operating condition at all times, even in highly variable conditions.
Specific control capabilities can include:
Air/fuel ratio control based on the single variable of charge-air density, able to maintain NO x within extremely tight tolerances under all load conditions and regardless of changes in ambient conditions
Detonation sensing and timing compensation by individual cylinder for optimum engine protection
Block loading and unloading without significant changes in speed, thus providing smaller voltage fluctuations.
Simplicity and flexibility
While some maintenance operators accustomed to monitoring and adjustment of manual engines were apprehensive about electronic control at first, the simplicity of its operation in most cases made them believers. There is nothing to adjust or service, except that a diagnostic check of the control system is recommended at the time of engine overhaul in much the same way as an automotive mechanic plugs a late-model car into an engine analyzer during a scheduled maintenance visit.
Modern controls not only eliminate maintenance of electronics and ignition systems but also greatly simplify maintenance of the entire engine. The system compensates instantly and effortlessly for changing operating conditions. The control system triggers alarms and fault codes for a wide range of engine problems such as an air-fuel ratio falling outside the prescribed range or excessive exhaust temperature.
Laptop PC-based tools can be used to perform system diagnostics, examine fault codes, and observe operating trends. Such tools can also be used to change engine operating characteristics. For example, manufacturers’ latest enhancements to the engine operating maps, or changes in the maps to suit a specific application, can be added with simple flash programming without opening the control module.
Programmability also allows users to add capabilities, such as an automatic cool-down cycle before shutoff, or a purge cycle that cranks the engine at startup with the fuel valve closed, clearing any fuel gas that might be in the exhaust system.
In addition, the control unit enables remote monitoring of critical engine functions by way of a communication link that sends data via a modem. An engine user thus can monitor generator sets in a factory from an office at corporate headquarters, or have the monitoring performed by a third party at a central control center.
Most control modules themselves are extremely robust, because they are contained in environmentally sealed housings, fully functional at extreme temperatures, and impervious to electromagnetic interference. The units generally are battery-powered, so they are extremely forgiving of voltage changes. If power to the control module is lost, the system retains all settings and data in memory — no reprogramming is necessary.
Electronic control is helping to make onsite power generation more economically viable for industrial energy users. Sophisticated electronics have made generator sets not just simpler to maintain, but more emissions-compliant and more efficient than ever.
Companies seeking to gain a competitive edge by increasing their energy self-sufficiency or by getting electric power at market-beating prices can readily look at onsite generation as a strategic business investment.
Author Information Michael J. Reinhart is a Senior Gas Product Consultant with the Electric Power Group of Caterpillar Inc., based in Mossville, IL. He specializes in the definition of new products and has had extensive experience in the service and applications of Cat G3500 Series gas engines.