Blended hydrogen–natural gas-fueled internal combustion engines and fueling infrastructure

Many different blends of conventional and alternative fuels have previously been investigated to gain advantages of lower tailpipe and greenhouse gas emissions while reducing petroleum dependence. In particular, blends of hydrogen with compressed natural gas (HCNG, H2CNG, and Hythane®) have demonstrated advantages of lower tailpipe emissions and in some cases higher fuel economy. HCNG with hydrogen concentrations from 0% to 20% by volume can be run in conventional gasoline engines without retuning. HCNG with concentrations of hydrogen above 20% require engine retuning and low swirl intakes to run optimally. Achieving low levels of unburned methane emissions is a significant challenge for most conventional fuels without hydrogen enrichment. Hydrogen enrichment in HCNG blends promotes rapid and more complete combustion of methane by providing an abundance of hydroxyl ions, greatly reducing fugitive methane tailpipe emissions. HCNG engines are largely unaffected by carbon monoxide (CO) contamination in fuel, while by comparison hydrogen proton exchange membrane (PEM) fuel cells are permanently damaged by CO contamination as low as 10ppm. HCNG borrows heavily from existing technology for CNG and hydrogen engines, storage, and dispensing stations. An exception is the need for a specialized hydrogen and natural gas blending unit before or after compression. HCNG achieves higher energy storage density than hydrogen within the same tank volume and pressure. Therefore, HCNG engine-powered vehicles deliver significantly greater range compared to hydrogen engine-powered vehicles with equivalent onboard storage tank volume. HCNG vehicles and fueling infrastructure have been successfully demonstrated across the globe in a number of transit and light vehicle fleets. HCNG-fueling infrastructure is usually deployed in stations where hydrogen and compressed natural gas fueling already exist. Use of HCNG can help accelerate the early market growth for hydrogen prior to widespread deployment of fuel cell vehicles and hydrogen-fueling infrastructure.