Planning an Emissions Retrofit? Start with These Five Questions

When an emissions retrofit becomes necessary, the pressure to find a solution can build quickly.

A regulation may have changed. An operating modification may have triggered a new review. A company may have established a more aggressive emissions goal. Whatever brought the project forward, the conversation can quickly move to equipment, controls, catalysts, and cost.

But selecting a technology is not the best place to begin.

According to GMRC Subject Matter Expert Hans Mathews, properly scoping the project is often the most difficult and important part of an emissions retrofit. Once engineers determine what needs to be done, the detailed engineering may involve more work, but the project has a clearer direction.

Before recommending a retrofit approach, engineers need to understand the requirement, the equipment, and the result they are expected to deliver.

These five questions can help establish that foundation.

1. What Are You Trying to Achieve?

“Reduce emissions” may describe the general assignment, but it does not define the engineering objective.

Start by identifying the specific result the project needs to deliver and the requirement driving it.

• Which emissions must be reduced?
• What performance level must the equipment achieve?
• Is the target based on a regulatory requirement, customer requirement, or company initiative?
• How will the required result need to be demonstrated?
• Does the change apply to one unit or an entire station?
• Are reliability, efficiency, or future operating flexibility also part of the decision?

The distinction matters. A regulatory requirement and an internal company goal may both lead to an emissions project, but they may not create the same design constraints, testing requirements, or range of possible solutions.

Defining the objective and requirement early helps establish what success looks like before the team begins evaluating technologies.

2. What Is the Equipment Telling You?

An emissions retrofit should not begin with the assumption that every engine, or every unit at a station, needs the same solution.

Before recommending changes, engineers need to understand how the equipment is operating today. That includes examining the combustion process and the factors influencing emissions performance.

Depending on the application, that may include evaluating:

• Air-fuel ratio
• Ignition energy and performance
• Engine loading and operating patterns
• Existing control systems
• Combustion stability
• Equipment configuration
• Current emissions data

What appears to be the obvious solution isn’t always the right one. Understanding the equipment and its operating conditions can reveal opportunities or limitations that aren’t immediately apparent.

3. What’s Driving This Recommendation?

Modern emissions technologies give engineers a variety of options, including combustion controls, catalysts, air-fuel ratio technologies, ignition improvements, and equipment modifications.

But having options isn’t the same as having the right answer.

No single solution works for every engine or application. A recommendation should reflect the operating conditions, project requirements, and the way the equipment is expected to perform after the upgrade.

Before moving forward, ask:

• Why does this recommendation fit this application?
• What operating conditions influenced the decision?
• How does the proposed approach address the project objective?

Hans repeatedly returns to the same principle: Everything is governed by physics.

A sound recommendation isn’t based on preference or familiarity with a particular technology. It’s based on understanding the equipment, applying engineering principles, and selecting the approach that best fits the situation.

4. Have You Properly Scoped the Project?

Knowing how to scope the project is one of the most valuable skills an experienced emissions engineer develops.

As Hans explained, once engineers determine what needs to be done, the detailed engineering may involve considerable work, but the project has a clearer direction. The difficult part is knowing what needs to happen before that detailed engineering begins.

Experienced engineers develop that judgment through repeated exposure to different equipment and real retrofit projects. They learn how to assess an unfamiliar application, apply the governing physics, and determine what needs to happen next.

If the scope is wrong, even well-executed engineering can lead the project in the wrong direction.

Before moving forward, the team should be able to clearly explain what must be achieved, what the equipment is telling them, and why the proposed direction makes sense.

5. Should You Retrofit or Replace?

Before committing to a retrofit, consider another question: Does upgrading the existing equipment make more sense than replacing it?

That decision involves more than emissions performance alone. Engineers and operators may also need to consider:

• The scope and cost of the required retrofit
• The cost of replacement equipment
• Equipment availability and lead times
• Whether upgrading the existing equipment provides a practical alternative to replacement

Hans notes that replacement equipment has become significantly more expensive and may carry long lead times. In some applications, that can make upgrading existing equipment an attractive option.

But the decision depends on the equipment, the operating requirements, and the economics of the specific project. The goal isn’t to retrofit at all costs. It’s to determine which path makes the most sense for the application.

Take the Next Step

Emissions retrofit decisions depend on understanding the equipment, the requirement, and the technologies available to address it.

Continue exploring those considerations at the 2026 Gas Machinery Conference, October 4–7 in Indianapolis, where emissions and regulatory compliance are among this year’s technical program tracks.

Explore GMC 2026

This article draws on insights Hans shared as part of GMRC’s Subject Matter Expert Knowledge Transfer initiative.