Hydrogen blending vs waste-heat recovery in large dual-fuel engines: A prospective lifecycle techno-economic and probabilistic assessment
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DOI: 10.67571/njeru.2025.010818
Published: May 1, 2025 | Issue: Volume 2, Issue 1
Page No. 8–18
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Email: samueloliver@unicross.edu.ng
1 Department of Mechanical Engineering, Faculty of Engineering, University of Cross River State, Calabar - Nigeria.
Received: March 20, 2025 Reviewed: April 22, 2025 Accepted: May 1, 2025
Abstract
Hydrogen blending is increasingly proposed as a near-term route for decarbonising gas-fired power and propulsion systems, but volumetric blend percentages are often interpreted as equivalent energetic substitution. This study asks a practical design question: under what conditions does hydrogen blending provide greater climate and economic value than recovering exhaust heat from a large dual-fuel engine? A prospective cradle-to-busbar model was developed for an 18V50DF-class engine using an official simple-cycle efficiency of 49.4% and a waste-heat-recovery efficiency ceiling of 54.0%. Hydrogen fractions of 0-30 vol% were converted to energy shares using lower heating values, and lifecycle greenhouse-gas (GHG) intensity included combustion CO2, upstream natural-gas emissions, methane slip, hydrogen production emissions and the indirect warming effect of hydrogen leakage. Fuel cost, annualised waste-heat-recovery cost and carbon cost were evaluated alongside a 50,000-sample uncertainty analysis. Twenty vol% hydrogen supplied only 7.01% of fuel energy. In the central case, it lowered GHG intensity from 514.3 to 489.4 g CO2e kWh-1 (4.8%) but increased cost from 8.10 to 9.31 US cents kWh-1 at a US$50 tCO2e-1 carbon price. Waste-heat recovery alone reduced GHG intensity to 470.5 g CO2e kWh-1 (8.5%) and cost to 7.69 US cents kWh-1. The combined 20 vol% H2-WHR case reached 447.8 g CO2e kWh-1 (12.9%). The central break-even hydrogen price was US$1.19 kg-1, and hydrogen carbon intensity had to remain below 8.27 kg CO2e kgH2-1 for net climate benefit. Within the adopted uncertainty distributions, waste-heat recovery dominated the baseline on both metrics in 99.4% of samples, compared with 0.1% for hydrogen blending alone. The results support an efficiency-first hierarchy: recover avoidable heat before using scarce low-carbon hydrogen, unless hydrogen is demonstrably low-cost, low-emission and operationally compatible with the engine.
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