The upcoming EPA emissions standards slated for 2027 are set to reshape the landscape of fire apparatus engines. This article discusses what these new guidelines mean for engines, cab and chassis design, and apparatus bodies, drawing on expert insights to help fire service professionals navigate this transition.

Why Are the EPA Standards Changing?

For several decades, engine emissions standards have been steadily tightened to reduce pollutants, particularly nitrogen oxides (NOx). Since 1988, regulations cut NOx emissions by approximately 80%. In 2027, the EPA and California Air Resources Board (CARB) are aligning on a further 80% reduction target within just four years. Such a dramatic drop—from 200 mg to 35 mg of NOx emissions per horsepower-hour—represents a steep technical challenge.

Chris Crowel, Emergency Vehicles Lead at Cummins, explains the magnitude of this change. The first drop in emissions was costly but achievable. Now, pushing that second 80% reduction requires completely new engine designs. Additionally, these standards extend warranty periods for emissions components from five to ten years and impose stricter compliance requirements. Engines must meet emissions across the entire operating range rather than relying on emissions averaging.

One Engine Manufacturer’s Approach

Cummins is responding with a $2 billion investment in research, development, and manufacturing enhancements to deliver a new generation of fire apparatus engines. Existing engines like the B6.7, L9, X12, and X15 will be replaced with all-new platforms, including the AB7.2 (a 7.2-liter displacement engine) and the X10 (a 10-liter engine replacing the L9 and X12).

Several key technological innovations are driving these new engines:

Dual SCR Catalysts in One Module: To meet the low emissions thresholds, the after-treatment system will feature two Selective Catalytic Reduction (SCR) catalysts housed together, sometimes called a “snowman” or “infinity” design, increasing reaction surface area while managing packaging constraints.

Advanced After-Treatment Heaters: New heater elements before the Diesel Particulate Filter (DPF) and SCR catalysts will help engines meet emissions standards earlier after startup, but these require significant electrical power. Therefore, Cummins will add a belt-driven 48-volt alternator dedicated to generating this heat.

Clean-Sheet Engine Design: Leveraging computer-aided design (CAD), engineers have optimized material placement, improving cooling, oil flow, and block stiffness. For example, moving the gear train from the front to the rear reduces potential oil leaks and enhances durability.

Weight Management: Despite adding emissions hardware, the new X15 engine system will be roughly weight-neutral compared with current setups. The X10 engine will be about 300 pounds heavier than the L9 but similar to the current X12, which is itself lighter than most mid-bore engines in the market.

Improved Engine Performance: The X15 will maintain familiar horsepower and torque ratings, including the 605-hp/1,850 ft-lb rating popular in fire service applications. The X10 will cover all previous L9 ratings with a new high-torque family offering up to 1,650 ft-lb, close to the X12’s current capability.

Environmental Improvements: Moving to canister-style oil and fuel filters, replacing steel housing and elements separately, supports environmental sustainability through reduced waste.

Cummins plans to launch the new X15 as early as April 2026, ahead of the 2027 mandate, giving manufacturers time to prepare. However, the last date to build with the current L9 engine frame will be December 31, 2026.

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