How accurate is your ECM Fuel data?
This blog post discusses the contrasting fuel measurement strategies in mining. The three most common fuel measurement strategies employed in mining include measuring at the time of fill-tank fill measurement, Engine Control Module (ECM) fuel consumption estimates, and on-equipment fuel measurement. The blog post discussed the benefits and shortcomings of each approach.
1. Engine control module (ECM) fuel consumption estimates
If an engine is electronically fuel injected, the computer controlling this process inevitably keeps tabs on how much fuel has been dispatched. The engine manufacturers construct models that relate the time a fuel injector is held open to the amount of fuel expected to flow across the injector opening. These models are executed in real-time and add tiny sums to the fuel accumulator value every time an injector is fired. In general, the OEMs do a pretty good job of it, but as with any model, their accuracy depends on how closely certain design assumptions align with reality. Under actual-world conditions, fuel injectors age and foul, fuel pressures modulate, and cylinders begin to lose compression. As these changes unfold, the model’s relevance diminishes. Suppose you were to consider the combined effect of these factors across a fleet of variably aged equipment from various manufacturers. In that case, you can expect severe shortcomings in the accuracy and repeatability of the ECM fuel consumption estimates.
In practice, Cascadia Scientific has compared ECM fuel numbers to measured fuel values using fuel flow meters over the same time. In summary, the accuracy of the ECM-modelled consumption varies considerably between engine modes, at times underestimating and at other times overestimating the fuel consumed. While these errors partially cancel over extended time frames, they can lead to significant deviations over shorter spans, which considerably limits the granularity of analysis achievable if ECM consumption is relied upon in isolation.
Chart 1: ECM Fuel Consumption vs Measured Fuel Consumption at a Canadian Open pit mine
|Model||Measured Fuel Rate (l/h)||ECM Fuel Rate (l/h)||Error (l/h)||Percentage Error|
2. Tank Fill Measurements
If accuracy is the undoing of ECM fuel estimates, it is the most significant advantage of tank fill measurement. Unlike the fuel that flows through on-equipment meters, all the fuel through a fill station meter is bound for a single destination. In the absence of fuel leaks and theft, 100% of the fuel dispensed to a piece of equipment will be duly consumed. As an additional benefit, because the amount of fuel fed to a truck is the same amount of fuel removed from the depot, tank fill measurements help keep tabs on storage levels. The downside is that while this approach provides an exceptionally accurate measurement of a particular quantity: “the amount of fuel consumed by a piece of equipment since its last fill, provided the equipment was filled to the same level on both occasions,”… this value does not provide the necessary granularity to target specific characteristics of mining equipment and daily operation. A typical fueling strategy might see a truck replenished once per day. Over that day, the truck might complete 50 haul cycles of various lengths, vertical travel, and payload and be operated by four or more individuals, idling between 10% and 40% of the time.
3. Direct Fuel Measurement
Direct measurement of diesel fuel consumption can be a challenging task. Diesel engines are fed considerably more fuel than consumed, with the balance returned to the tank. This oversupply is essential as it extracts heat from engine components (e.g. Injectors, ECMs) and ensures the engine is never starved of fuel. It does, however, significantly complicate fuel measurement, which subsequently requires two meters; one to capture the volume of fuel fed to the engine and a second to capture the volume returning. The difference between these flows constitutes consumption, while the unburned fuel is noise. In the extreme case of motoring, fuel throughput can max out while the engine consumes no fuel. Fortunately, most mining engines spend comparatively little time under such conditions. Even so, the situation demands extremely accurate meters to ensure the noise does not overwhelm the measurement. Temperature poses the next challenge. Since the meters are volumetric, it is essential to measure fuel temperature to account for the drop in density which accompanies fuel heating across the engine.
In summary, direct fuel measurement is a complicated task. Still, the combined benefit of high measurement accuracy and sampling frequency makes this approach the best option for pursuing data-driven efficiency gains in the modern mine.