Managing Ignition Quality in an Increasingly Variable Marine Fuel Market

Marine fuel has always varied from bunker to bunker. Over the past several years the complexity of the fuel itself has changed.

The introduction of very low sulfur fuel oil (VLSFO), greater refinery optimization, and the increasing use of renewable blending components have fundamentally changed how marine fuels are produced. Today's marine fuels are often blended from a broader range of refinery streams than in the past, resulting in greater variation in fuel composition, combustion characteristics, and onboard handling requirements. (CIMAC)

Most of these fuels comply fully with ISO 8217.

That does not necessarily mean they will all perform the same once they reach the engine.

The International Council on Combustion Engines (CIMAC) has acknowledged this challenge, noting that current commercial fuel specifications cannot reliably predict ignition and combustion performance. In some cases, fuels that fully comply with specification have still resulted in operational problems, engine damage, and even complete engine failure due to poor combustion characteristics. (CIMAC)

For ship operators and technical managers, this raises an important question:

How prepared are you if your next bunker exhibits marginal ignition quality?

Why Ignition Quality Matters

Diesel combustion begins with ignition.

After fuel is injected into the combustion chamber, there is a short period before combustion starts. This is known as the ignition delay. When ignition occurs too slowly, a larger quantity of fuel accumulates before combustion begins, producing a more abrupt pressure rise once ignition takes place.

The consequences can include:

• Rough combustion and diesel knock
• Increased soot and visible smoke
• Greater thermal loading
• Injector nozzle coking
• Carbonaceous deposit formation
• Reduced combustion stability during low-load operation

These effects may not immediately cause an engine failure, but over time they can contribute to reduced combustion efficiency, increased maintenance requirements, and shorter injector service life.

Engine manufacturers have long recognized the importance of fuel ignition quality to engine performance and reliability. Although acceptable ignition quality varies depending on engine design, operating conditions, and fuel grade, OEM guidance consistently identifies poor ignition quality as a contributing factor to unstable combustion, increased emissions, deposit formation, and accelerated component wear. Where fuel ignition quality is found to be marginal, corrective actions may include fuel replacement, blending, or other fuel management practices to restore acceptable combustion performance.

Specification Compliance Is Only the Starting Point

ISO 8217 remains the global benchmark for marine fuel quality. However, it was never intended to predict every aspect of engine performance.

As fuel composition has become increasingly diverse, engine manufacturers, fuel testing laboratories, and industry organizations have emphasized that compliance with fuel specifications should be viewed as the starting point—not the end point—of effective fuel management. (CIMAC)

The industry's response has been to place greater emphasis on fuel testing, segregation, compatibility assessment, contamination monitoring, and onboard fuel treatment.

Ignition quality deserves to be considered part of that same strategy.

When Ignition Quality Becomes a Concern

When laboratory testing or onboard performance suggests marginal ignition quality, operators generally have four practical options.

1. Reject the fuel
   

   From a technical standpoint, rejecting an off-specification bunker is often the preferred solution.

   Operationally, however, once fuel has been transferred onboard, debunkering, replacement fuel procurement, and voyage delays can quickly become prohibitively expensive.

2. Blend with another fuel
   

   Blending with a fuel of better ignition quality may improve combustion performance.

   However, this approach requires suitable fuel availability, available tank capacity, compatibility assessment, and careful blend calculations. Improper blending may introduce additional risks, including instability, sludge formation, filter blockage, and asphaltene precipitation.

3. Burn the fuel untreated
   

   Many vessels ultimately consume the fuel as delivered.

   While this may be operationally necessary, it also means accepting the combustion characteristics of that fuel and the potential for increased smoke, injector deposits, harsher combustion, and additional maintenance.

4. Improve combustion before the fuel reaches the engine
   

   A fourth option is to improve ignition quality through fuel treatment.

   Rather than altering the fuel specification itself, cetane improver chemistry promotes earlier auto-ignition after fuel injection, reducing ignition delay and producing a more controlled combustion event.

   For operators who cannot reject or blend a marginal bunker, this provides an immediate onboard mitigation strategy.

Beyond Ignition Improvement

Modern cetane improvers are capable of providing benefits beyond simply shortening ignition delay.

MAXIBURN™ CI (Cetane Improver) combines nitrate-based ignition improver chemistry with detergent technology designed to reduce injector deposits and maintain injector cleanliness during continued operation. The ashless formulation is fully soluble in marine fuels, including VLSFO, ULSFO, marine distillates, residual fuels, and bio-derived fuel blends.

Maintaining injector cleanliness is particularly important because injector deposits gradually distort fuel spray patterns, reducing combustion efficiency and increasing soot formation even when the fuel itself remains unchanged.

Standardized engine testing demonstrated approximately 86% reduction in injector nozzle fouling compared with untreated fuel. Additional dynamic engine testing showed improved injector keep-clean performance and reduced power loss associated with deposit formation.

How much improvement should I expect?

There is no single answer.

Fuel response depends on several characteristics of the untreated fuel, including its composition, density, existing ignition quality, and additive treat rate.

Rather than assuming every bunker behaves identically, predictive response models developed from laboratory testing can be used to estimate expected cetane improvement based on the characteristics of the fuel being treated. This allows the treat rate to be selected based on the fuel onboard and the desired performance response rather than relying solely on a universal dosage.

Drew Marine can assist customers with this evaluation. Fuel analysis information, including available ignition quality and density data, can be reviewed by Drew Marine's fuel specialists to help determine an appropriate treatment strategy. Customers and vessel personnel can access this support remotely through the IMO2020 Helpdesk at IMO2020@drew-marine.com.

This remote assistance resource can also support broader fuel-related questions, helping vessel operators interpret fuel analysis results, identify potential fuel quality concerns, and determine when treatment or further investigation may be appropriate

Preparing for an Increasingly Complex Fuel Market

Marine fuel is unlikely to become less complex.

As refineries continue optimizing production and the use of renewable blend components expands, operators should expect fuel variability to remain a normal part of vessel operations. (CIMAC)

Most vessels already prepare for known fuel risks by carrying products to address microbial contamination, water ingress, fuel instability, and cold-flow performance.

Ignition quality deserves the same level of consideration.

Carrying a cetane improver is not an expectation that every bunker will perform poorly. It is recognition that fuel quality has become more variable, and that operators are increasingly expected to manage that variability rather than simply react to it.

For today's fleet, combustion performance is no longer determined solely by the engine—it begins with the fuel.