The reduction in carbon emissions from transportation industry vehicles has been significantly influenced by market forces, often preceding government legislative efforts. The evolution of heat-driven engines, beginning with Thomas Newcomen’s fire-powered steam engine in 1712, marks the start of this journey. These early engines, fueled by wood and later coal, had low energy efficiency and high carbon emissions
Efficiency improvements in engine technology played a crucial role in reducing emissions. The transition from wood to coal as fuel led to the development of higher-pressure steam engines with improved thermal efficiency. The advent of tripleexpansion steam piston engines and steam turbine engines in the early 1900s further enhanced efficiency, reducing carbon emissions per unit of power generated. The introduction of diesel engines in the 1930s, which operated at over 30% thermal efficiency, marked a significant advancement. Diesel engines, particularly those used in maritime propulsion, were more efficient and emitted less carbon compared to their wood or coal-powered predecessors.
Modern engine efficiency has seen remarkable improvements, especially in the maritime sector. Today, large-scale modern piston engines can convert diesel fuel to propulsive power at 50% efficiency, with potential for further improvement. Similarly, large-scale gas turbine engines operate at near 50% thermal efficiency, burning a variety of fuels. Electrification has also contributed to efficiency gains. Electric trains powered from overhead cables and electric vehicles recharged from efficient power stations represent a shift towards more sustainable transportation modes. However, the overall energy efficiency from source to propulsion can be below 20% for hydrogen fuel cell vehicles.
The search for cheap fuel alternatives has historically driven innovation. During the 1940s, gasoline rationing led to the exploration of fuels like propane, which emitted lower carbon emissions and was cheaper to produce. Recent research has focused on carbon-free fuels like hydrogen and ammonia. Hydrogen, used in modified internal combustion engines or fuel cells, emits zero carbon emissions. Plans for ammonia- powered container ships and adaptations of internal combustion engines for maritime propulsion and aircraft to use hydrogen as fuel are underway. However, the lower energy storage density of carbon-free propulsive systems poses challenges, particularly for the maritime sector, which may need to explore alternatives like mega-size tug-barges for extendeddistance ocean service. These tugs, powered by carbon-free technologies, could initially operate in inland waterways, North America’s Great Lakes, and domestic coastal service.
