Full-scale experimental performance of a charcoal-fired mobile fire-tube boiler for steam-powered vehicle applications

This study presents a performance-oriented experimental assessment of a full-scale charcoal-fired steam-powered vehicle incorporating a three-pass fire-tube boiler, a converted automotive steam engine, and a mechanical drivetrain. The investigation focuses on measured thermal behavior, vehicle-level fuel utilization, bounded sensible stack-loss assessment, and the physical plausibility of the estimated thermal supply relative to vehicle operation. During cold-start operation, the boiler required approximately 150–160 min to approach the nominal operating pressure of 10 bar, reflecting the large water inventory and thermal inertia of the full-scale system. During subsequent quasi-steady operation, the boiler pressure remained within approximately ±0.5 bar of the nominal operating level, while the stack-temperature response reflected the transition from warm-up to sustained steam generation. Vehicle testing produced a maximum observed speed of approximately 34 km/h under unloaded conditions. Distance-based fuel utilization was evaluated from measured charcoal consumption and vehicle travel distance. Charcoal consumption increased approximately linearly with distance over the investigated operating range, corresponding to a distance-based specific fuel consumption of approximately 12–14 kg/km and an average value of 12.9 kg/km. This result indicates the high fuel demand associated with the present manually fired prototype and is reported as a vehicle-level fuel-utilization metric rather than as a thermal-efficiency measure. Boiler thermal behavior was further assessed using a bounded sensible-stack-loss approach based on measured stack temperature and stated assumptions for charcoal higher heating value and excess air. The estimated sensible stack-loss fraction was approximately 0.14–0.18, giving a complementary stack-loss-based thermal-performance indicator of approximately 0.82–0.86 (82–86%). This indicator represents only the complement of the estimated sensible stack loss and should not be interpreted as overall boiler efficiency, because other energy-loss mechanisms were not quantified. The steam-generation rate was estimated from an energy-balance approach to be approximately 200–300 kg/h and should be regarded as an engineering estimate rather than a directly measured boiler-capacity value. The estimated thermal-supply scale and the independently observed vehicle operating behavior were considered together only within a first-order physical-plausibility assessment. No quantitative relationship between steam generation and vehicle speed was inferred because steam mass flow, engine indicated performance, shaft torque, and drivetrain efficiency were not independently measured. Overall, the results demonstrate stable operation of the full-scale charcoal-fired steam propulsion platform while identifying long warm-up time and high distance-based fuel demand as major performance limitations. The study further demonstrates the importance of distinguishing directly measured quantities from bounded and indirectly estimated performance indicators when evaluating full-scale mobile steam systems with limited instrumentation.