Analytical Investigation of Methane Slip in Gas Engine Power Plants in Nigeria: Causes, Quantification, and Abatement

Methane slip, defined as the unburned methane emitted through the exhaust of gas engine power plants, represents both a greenhouse gas concern and a combustion efficiency loss that has received limited empirical attention in the Nigerian context. This study analytically investigates methane slip from gas engine-based power plants operating in Nigeria, drawing on data from facilities in Imo, Ogun, and Kano states that collectively represent diverse operational profiles and engine technologies. The research employs a multi-method analytical approach combining exhaust gas measurements using portable flame ionisation detectors (FIDs), engine performance modelling using GT-Power simulation software, and statistical analysis of the relationship between operating parameters and slip magnitude. Methane slip is quantified under varying load levels (25, 50, 75, and 100 percent rated capacity), gas compositions, air-fuel ratio settings, and valve timing configurations. The study fills a research gap in the literature by providing Nigeria-specific methane slip characterisation data for stoichiometric and lean-burn engine types operating in tropical ambient conditions. Findings reveal that lean-burn engines operating below 60 percent load exhibit methane slip rates up to four times higher than at full load, with slip values between 1.8 and 3.2 percent of fuel methane input, significantly affecting the lifecycle greenhouse gas performance of these systems. Air-fuel ratio optimisation is identified as the most cost-effective abatement measure. Recommendations include mandatory methane slip reporting for gas engine plants above 1 MW capacity and industry adoption of methane slip benchmarking under the Nigeria Carbon Market Activation Framework. Keywords: methane slip, gas engine, greenhouse gas, combustion efficiency, power generation.