Using Technology to Optimize Fuel Injection

Creating an efficient, durable fuel injection system is no simple task—especially for our opposed-piston, two-stroke diesel engine. The reason: our injection geometry is completely different. Unlike conventional engines, which inject through the cylinder head towards the piston, the Achates Power engine lacks a cylinder head so injection comes from the side, between the pistons and into the swirl.
 
In designing the optimal fuel injection system—for our engine or any other—there’s a lot to consider, including the number of injectors, the number of holes per injector, the size and orientation of the holes, the number of injection events, and the timing and sizing of those events. The air motion caused by the interaction of swirl with the combined piston motion, and its effects on air and fuel mixing, must also be considered.
 
With this in mind, Achates Power built its own state-of-the-art fuel lab. The lab contains all of the equipment we need to characterize the fuel spray and ensure proper operation of the fuel injection equipment on the engine itself. We use the fuel spray characterization to calibrate our spray models for chemically reactive computational fluid dynamics (CFD), enabling us to analytically design and optimize our combustion system.
 

Using a shadow imaging technique, we can produce a qualitative assessment of the spray pattern, including its penetration, cone angle and cone separation angle. Laser Induced Fluorescence (LIF) allows Achates to visualize fuel concentration at various regions in the spray. For a more quantitative assessment, a Phase Doppler Anemometry (PDA) setup is employed to obtain droplet size and velocity at various points in the spray. The data obtained is used to validate spray models built in Converge and KIVA-3 software for reactive combustion analysis. And from these models, we can predict the combustion system performance of the engine.
 

The fuel lab also includes a fuel bench, which enables us to measure injected volume/mass for a given rail pressure and commanded actuation time. The injection measurement is achieved using an Injection Flow and Rate (IFR) fixture. The IFR is capable of measuring the injection rate and volume of each injection event. All electronic parameters are captured including the beginning of current to beginning of injection delay, rise rate, fall rate, injection duration, and shot-to-shot data.
 

Building, maintaining and utilizing a fuel lab is a significant commitment, which is why few companies—outside of fuel injector manufacturers—undertake the challenge. By leveraging the technologies in our fuel lab, and the expertise of our scientists and engineers, Achates Power has successfully demonstrated that our engine is clean, lower cost and significantly more fuel efficient. For a behind-the-scenes look at the fuel lab, we invite you to view the video on our website or YouTube channel.