Stoichiometric engines have very low emissions by way of a three-way catalyst, but suffer from lower efficiencies in particular at part load. Lean-burn engines deliver good fuel economy by running unthrottled, but they require very expensive aftertreatment to meet emission requirements. It was clear we had to combine the best attributes of each approach, so we chose to apply our Hydraulic Valve Actuation system to eliminate the throttling losses, with a simple three way catalyst to clean up remaining emissions. The camless engine combines the benefits of Lean-Burn and Stoichiometric Natural Gas Engines.

—Miguel Raimao, responsible for Business Development at Sturman

The stock production diesel engine was fitted with a commercial natural gas fuel system and Sturman’s Hydraulic Valve Actuation (HVA) system which provided independent control of valve timing, duration and cylinder de-activation capability. The proprietary Sturman Total Engine Controller (STEC) was used to control the stock turbocharging and EGR systems.

These Sturman controls allowed the project team to increase the compression ratio from the typical 10:1 to 14:1. HVA allowed the Sturman team to run the engine unthrottled and at times on only three cylinders to improve part load efficiency. Stoichiometric combustion was optimized at all operating conditions without the risk of knock, eliminating the need for costly lean NO_x aftertreatment.

The ability to meet low emission requirements at high efficiencies without a cumbersome and costly SCR system will be a game-changer for both the power generation and transportation sectors. In particular, this technology is a solution for California’s interest to utilize biomethane, also known as renewable natural gas. For example, this engine can respond to the varying qualities of renewable natural gas produced at a landfill, and then efficiently generate electricity on the spot.

—Joe Vollmer, Director of Government Affairs for Sturman Industries

The program with the CEC focused specifically on the application of Sturman’s advanced mobile HVA technology to stationary power generation. For a long time, engine manufacturers have customized engines for specific applications, making low-volume versions for power generation considerably more expensive than those for on-highway applications. The flexibility afforded by HVA offers the potential to optimize a single engine for a variety of applications through simple software calibration, Sturman says.

For example, where a power generation engine might be equipped with a particular camshaft for constant speed operation, and a mobile engine might have an entirely different camshaft for varying engine speed, HVA supports both with the same hardware. Even engine braking functionality for mobile applications is inherent to every HVA system—it is accomplished through software.

Sturman is installing the engine in a demonstration vehicle, adding high-pressure direct injection, and installing HVA on larger engines for power generation, gas compression and mobility.

Sturman has been developing Hydraulic Valve Actuation since 1995.