Cummins Advances Engine Performance with Two-Stage Turbocharging

Cummins Turbo Technologies is innovating with two-stage turbochargers for medium-heavy duty engines, building on decades of Holset® turbocharger reliability. These systems use two turbochargers in series to boost engine power and efficiency, crucial for meeting modern emissions standards and fuel economy demands.

How Two-Stage Turbocharging Works:

Unlike single-stage turbos, two-stage systems employ a smaller, high-pressure (HP) turbo and a larger, low-pressure (LP) turbo. Exhaust gas first drives the HP turbine, which powers the HP compressor to pre-compress air from the LP compressor. The remaining exhaust energy then drives the LP turbine and compressor for further air pressurization. Bypass valves optimize performance across engine speeds, directing exhaust flow to either turbo as needed. This balanced approach enhances low-end torque, peak power, and altitude performance.

Types of Two-Stage Systems:

Cummins utilizes various two-stage configurations including:

• Sequential: Smaller turbo for low speeds, larger for high speeds, minimizing lag.
• Compound: Series setup for heavy-duty applications, maximizing boost and efficiency.
• Parallel: Dual turbos for V-engines, balancing power and response.
• Variable Geometry (VGT) in Two-Stage: Combining fixed and VGT turbos for optimized performance across speed ranges.

Advantages:

Two-stage turbochargers offer superior performance by:

• Improving fuel efficiency.
• Balancing low-end torque and high-end power.
• Enhancing performance at high altitudes.
• Providing quick torque response.
• Achieving high compression ratios efficiently.

Challenges:

Despite benefits, two-stage systems present engineering challenges:

• Packaging Constraints: Integrating dual turbos can be difficult in various engine designs.
• Thermo-Mechanical Fatigue (TMF): Extreme temperature changes and stress require robust support structures. Cummins addresses this through extensive TMF validation.
• Wastegate Complexity: Managing exhaust flow with bypass valves, especially in sequential systems, adds control complexity. Cummins mitigates this through duty cycle validation and material selection.

Cummins overcomes these challenges through advanced engineering, rigorous testing, and material expertise, successfully implementing two-stage turbocharging to improve engine performance, efficiency, and emissions compliance across diverse engine platforms.