Compression-Ignition Engine Emissions Measurement Drift in Student-Built Dynamometer Laboratories for Engineering Education: A Reference-Gas Benchmark Linking Analyser Zero-Drift to Regulatory-Compliance Error Bounds

Student-built dynamometer laboratories are widely used in engineering education to teach compression-ignition engine testing and emissions measurement, yet the analysers in these facilities are rarely subjected to the drift audits that regulatory and industrial laboratories perform. No observational data are used or claimed: the analysis characterises the design under a declared variance structure with between-cluster SD = 6.0, residual SD = 4.5 and intraclass correlation = 0.640, across 2000 replications per design cell for cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. The results indicate that 52 clusters are required to detect a 5 percentage-point effect at 80% power, and that the minimum detectable effect at 80% power falls steeply as cluster count rises from 8 to 32. The reference-gas benchmark is a feasible and defensible addition to the engineering-education laboratory, and that its statistical design must be specified in advance if the resulting error bounds are to be credible to accreditation bodies.