Fuel Treatment for Diesel Fuel additives have become increasingly common in the marine diesel space, especially for small vessels and sailing yachts where fuel quality varies between marinas and bunker points. Fuel tanks may sit for long periods, and engines operate under suboptimal loads. While no additive can compensate for fundamental engine mechanical issues or poor maintenance, the correct formulations can improve reliability, reduce losses from fuel degradation, and, in certain conditions, enable marginal gains in efficiency. Understanding what each additive does, and more importantly, what it cannot do is essential for evaluating whether treatment is worthwhile.
Diesel fuel additives in yacht engines enhance performance and reliability by addressing contamination, lubrication, and stability. Biocides control diesel bug growth, stabilizers prevent oxidation, and detergents keep injectors clean. Cetane improvers aid combustion efficiency, while anti-gel agents protect in cold climates. Together, additives reduce maintenance issues, extend engine life, and safeguard against costly downtime.
Cetane improvers increase the fuel’s cetane number, shortening ignition delay and promoting more complete combustion. The most common compound is 2-ethylhexyl nitrate (2-EHN). Higher cetane values help engines start more easily in cold weather, reduce combustion noise, and stabilise performance at low loads, conditions typical of auxiliary diesels on sailing yachts that idle frequently or run at modest RPM.
Effect on efficiency: Cetane improvers do not increase the inherent energy content of the fuel but can slightly improve thermal efficiency by reducing misfire and incomplete combustion. Gains are typically small, often 1–3% in controlled conditions, but may be more noticeable in older engines or those experiencing marginal fuel quality. The main advantage is smoother operation rather than dramatic fuel savings.
Modern marine diesel contains detergent packages designed to prevent deposit formation on injectors, piston crowns, and valves. Additional aftermarket detergent additives are often based on polyetheramine (PEA) or similar molecules.
Dirty injectors can distort injector spray patterns, increase the fuel droplet size, and reduce atomisation quality. This leads to incomplete combustion, elevated smoke, and increased fuel burn. Detergent additives help remove these deposits gradually during operation.
Effect on efficiency: Keeping injectors clean helps maintain the combustion profile the engine was designed for. While additive detergents cannot repair worn injectors, they can mitigate fouling-induced inefficiencies. Efficiency gains of 2–5% are possible when injectors are moderately dirty, but gains are negligible if the system is already clean.
Ultra-low-sulphur diesel (ULSD) has reduced the natural lubricating properties because refining removes polar compounds that normally protect fuel pumps and injectors. Lubricity additives, commonly based on fatty acid esters, amine-based compounds, or acid ester chemistries, help restore boundary lubrication. Good lubricity reduces wear in injection pumps and high-pressure components, preserving injection timing and spray quality over time.
Effect on efficiency: Lubricity enhancers don’t directly change combustion efficiency. Their value is long-term, preventing wear helps the injection system maintain performance and fuel-consumption characteristics as the engine ages.
Water contamination, microbial growth, and acidic by-products from fuel degradation can corrode steel and aluminium components in storage tanks, fuel lines, and injection equipment. Corrosion inhibitors form a protective film on metal surfaces, preventing oxidation and reducing pitting.
Effect on efficiency: Corroded fuel lines or injectors degrade system performance, increasing consumption. By preventing corrosion, additives preserve designed fuel delivery characteristics, helping maintain consistent efficiency.
Diesel stored for long periods, common on yachts, undergoes oxidation, forming gums, resins, and particulate matter. Antioxidants slow this process, keeping fuel chemically stable. Stabilizers also help prevent stratification and the formation of insoluble compounds.
Effect on efficiency: Stabilized fuel maintains consistent combustion quality, avoiding issues such as sticking injectors, filter clogging, and poor atomisation. Efficiency benefits are preventive rather than additive: clean, stable fuel burns more reliably and predictably.
Diesel bug, microbial contamination at the water–fuel interface, is a significant issue on yachts with irregular fuel turnover. Bacteria and fungi create sludge that clogs filters, corrodes tanks, and chokes injectors. Biocides contain isothiazolinones or oxazolidines that kill microbial colonies.
Effect on efficiency: Biocides do not improve combustion. Their contribution to efficiency comes from preventing filter blockage, injector fouling, and poor combustion caused by contaminated fuel. In severe diesel-bug cases, using biocides can restore normal fuel burn that had previously worsened.
Water contamination, through condensation, poor fuel handling, or tank ingress, causes rust, microbial growth, injector damage, and reduced combustion quality. Demulsifiers help separate water from fuel so it can be drained, whereas water-dispersant additives break water into micro-droplets that pass safely through the system.
Effect on efficiency: Water reduces effective combustion temperature and interferes with fuel spray dynamics. Removing or dispersing water does not increase efficiency beyond normal levels, but it prevents serious losses and potential injector damage
When filling tanks, foam slows the fuelling process and can prevent accurate tank gauging. Anti-foam agents, usually silicone or polyalkylene glycol compounds, collapse bubbles.
Effect on efficiency: The is minimal and the benefit is operational rather than performance-related.
Cold-flow improvers modify wax crystal formation, allowing fuel to flow at lower temperatures by reducing cloud point and pour point. They are typically ethylene-vinyl acetate (EVA) copolymers.
Effect on efficiency: No direct impact and they ensure fuel delivery reliability in cold conditions, preventing filter plugging that would otherwise reduce power output and increase fuel consumption.
Many marine fuel treatments combine several functions, detergents, stabilizers, lubricity enhancers, corrosion inhibitors, and cetane improvers. Multi-function products appeal to yacht owners who want a “treat-and-forget” solution.
Effect on efficiency: Combined packages may yield a modest improvement in combustion stability and cleanliness. However, real efficiency gains depend heavily on initial fuel condition, engine state, and operational profile. In well-maintained engines running good fuel, improvements are modest. Typically, the most meaningful improvements come when:
Fuel treatment for diesel fuel, fuel additives can play a valuable role in preserving performance, preventing degradation, and stabilizing efficiency in small marine diesel engines. While they are not magic solutions and cannot compensate for mechanical wear or poor maintenance, the right formulations, particularly detergents, stabilizers, lubricity enhancers, and biocides, help ensure that fuel burns as cleanly and completely as possible. For sailing yachts, where fuel turnover is low and contamination risks high, additives often function more as protective measures than direct performance enhancers. Efficiency gains are typically incremental but can be meaningful when correcting underlying fuel-quality problems. Fuel Treatment for Diesel Fuel has useful benefits.