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102 vaporise without a heater to ensure it is warm enough, so the ECU must manage a heater control system as one of its outputs. Fortunately this is a rudimentary device, with the management strategy consisting largely of keeping the heater active until the CHT reaches a certain point. It can then be switched off until the CHT drops below the same threshold or a similar one, and logically these thresholds should differ depending on whether the engine is running, potentially at 120 C at start-up or perhaps 80 C while running. Another critical issue is fuel puddling. In the absence of direct injection, significant fuel wetting can occur in the cylinders of spark-ignited engines when using heavy fuel, as there is a distinct time lag between injection and combustion, and as discussed heavy fuel does not vaporise as readily as gasoline. To tackle this issue, one supplier has mapped a table for determining the size of fuel puddles according to rpm and throttle. In response, the ECU can command the fuel injectors to stop spraying during however many subsequent combustion cycles are necessary in order to allow the puddle of leftover fuel to burn before adding more, thus preventing a too-rich air-fuel mixture from entering the cylinder and affecting power output. This also allows a wider dynamic range of fuel injectors, enabling techniques such as skip-injection strategies during low-power modes, in which an injector will ‘skip’ a cycle if the amount of fuel required for the desired fuel efficiency is smaller than its minimum feasible output. Hybridisation is another trend that requires a lot of software reworking by ECU engineers. This entails that an ECU must be responsible not only for an engine but also a generator, in order to provide both steady horsepower and electrical current to the customer. Essentially, the latter is mapped around the duty cycle to be commutated on the motor/generator’s copper windings. Every generator running at a certain speed produces a certain voltage, and the duty cycle adjusts that voltage to the point that the ECU effectively determines whether to push current from the motor/ generator into the battery or pull it from the battery into the motor/generator. In this light, managing a motor/ generator is analogous to existing fuel engine management strategies. A hybrid powertrain ECU can track data inputs such as the load on the vehicle’s main battery and the speed of the crankshaft to determine whether the generator should be replenishing the battery. However, a hybrid ECU can also include new functionalities such as powering the motor/generator to support the throttle in driving the crankshaft. That could be critical for sustained flight in high altitudes where the air pressure is low, or for achieving high speeds at critical moments in defence, medical or search & rescue missions. To ensure that the electricity management and fuel-air management work in concert, an ECU might have its duty cycle mapped to target engine speed in particular, and the throttle width mapped to the target voltage. That means for instance that if the system is not producing enough electrical power, the throttle opens, the crank torque output increases and the generator outputs more power. The duty cycle keeps the voltage the same and increases the current coming out of the generator to replenish the battery and satisfy the load demand. April/May 2022 | Unmanned Systems Technology The use of CAN bus enables real-time access to subsystem diagnostics as well as transmission of higher data rates while needing fewer cable harnesses (Courtesy of Moscat Ingenieria) ECU makers are working harder to ensure the ECU does not fail, despite software updates ushering in the prospect of new bugs