10 FOGHORN many operators are considering options for what powers their vessels. The conversation is no longer just about compliance, it’s about strategy as fuel availability, lifecycle emissions, cost, vessel design, infrastructure readiness, and long-term viability all need to be considered. With both renewable and synthetic diesel options, plus emerging fuels such as methanol and ammonia being researched and tested, un- derstanding the differences between these alternative fuels and what they mean in practice is essential for making in- formed decisions. FIRST, HOW DID WE GET HERE? As operators well know, the shift toward alternative fuels didn’t happen overnight, it’s the result of years of tight- ening emissions standards that have steadily reshaped the marine landscape. In the U.S., the Environmental Protection Agency (EPA) has progressively reduced allowable emissions from marine diesel engines, targeting pollutants like nitrogen oxides (NOx) and particulate matter (PM). Over time, these lim- its have driven reductions of up to 82 percent in NOx and 98 percent in PM compared to earlier engine generations. Similar global standards, including IMO Tier III, have re- inforced the trend worldwide. To meet these requirements, engine systems have become more advanced. Technologies like improved fuel injection, turbocharging, and aftertreatment systems such as selective catalytic reduction (SCR) are now common. While effective, these systems add cost, complexity, and space requirements. At the same time, the focus has expanded beyond local emis- sions to include greenhouse gases. Even the cleanest diesel engines still rely on fossil fuels and reducing carbon output has become a central goal across the industry. For operators, this creates a dual challenge: meeting emissions standards today, while preparing for an even lower-carbon future. ALTERNATIVE DIESEL FUELS Today’s Drop-In Options For many, the most practical starting point today is drop- in fuels, which are alternatives that can be used in existing diesel engines with no needed modification. These include both renewable diesel and synthetic diesel options. Because these fuels are chemically similar to conventional diesel, they can be used without changes to engines, fuel systems, or onboard storage systems, making them attractive op- tions, as they don’t require extended downtime or complex retrofits to be introduced and result in lower emissions and virtually no particulate matter emission. Currently, the only performance drawback of these fuels is a lower energy den- sity that could result in up to a six percent power reduction for engines using lower-pressure unit pump fuel injection as compared to high-pressure common rail fuel systems. To create standard diesel, both the extraction of crude oil and the distillation of it during the refinery process results in a huge amount of CO2 emissions. By comparison, hydro- treated vegetable oil (HVO)—often referred to as renew- able diesel—is produced from feedstocks like used cooking oil, animal fats and other waste materials. It is created via hydrotreatment, which is the catalytic pro- cess of triglycerides to remove oxygen and break the feed- stock into straight-chained hydrocarbons known as paraf- fins. This refining process removes impurities and creates a clean-burning fuel that behaves much like traditional diesel, but with lower particulate emissions and cleaner combustion. In practice, HVO can reduce particulate mat- ter, carbon monoxide and hydrocarbons, often without noticeable changes in engine operation, other than the six percent power reduction. With both renewable and synthetic diesel options, plus emerging fuels … understanding the differences between these alternative fuels and what they mean in practice is essential for making informed decisions. FOGHORN FOCUS
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