Dual fuel injection compression ignition engine and method of operating same

What is this patent about?

’027 is related to the field of dual-fuel internal combustion engines, specifically those utilizing a combination of gaseous fuel, such as natural gas, and a liquid pilot fuel, like diesel, for compression ignition. In traditional dual-fuel systems, achieving a balance between high thermal efficiency and low emissions is difficult because gaseous fuels are hard to ignite and often result in high hydrocarbon output or excessive nitrogen oxides (NOx) depending on when they are introduced into the cylinder. The background context involves the challenge of managing the combustion rate and chemical reaction timing across a wide range of engine speeds and loads using a single injector hardware setup.

The underlying idea behind ’027 is to optimize the combustion process by dynamically splitting the gaseous fuel delivery into two distinct stages within a single power stroke: a pre-mixed charge and a post-ignition charge. By adjusting the mass ratio between these two quantities based on real-time engine speed and load data, the system can tailor the combustion environment. A small amount of liquid fuel acts as a chemical trigger, but the key insight is that the ratio of early-injected gas (which mixes thoroughly with air) to late-injected gas (which burns in a diffusion-like flame) allows the engine to switch between NOx-limiting and efficiency-maximizing strategies without hardware changes.

The claims of ’027 focus on a method and system for operating a dual-fuel engine where an electronic controller dictates a specific injection sequence. The independent claims require the controller to calculate and change a ratio of a pre-mix quantity to a post-ignition quantity of gaseous fuel as a function of engine speed or load. The sequence involves injecting the pre-mix gas first, followed by a pilot quantity of liquid fuel during an auto-ignition condition to trigger combustion, and finally ensuring the pre-mixed gas ignites only after the liquid pilot has successfully compression-ignited.

In practice, the invention utilizes a specialized dual-fuel injector capable of independent needle movements for gas and liquid. At high speeds and loads, the controller may also introduce a pre-mix quantity of liquid fuel early in the compression stroke. This early liquid fuel is kept below a specific threshold to prevent premature knocking, instead serving to accelerate the overall burn rate once the main pilot flame is established. This multi-stage approach allows the engine to maintain high power density at high RPMs while keeping emissions in check during low-load idling.

This approach differs from prior solutions that relied on either purely homogeneous pre-mixing or purely late-cycle direct injection. By utilizing a dynamic split-stream gaseous delivery, the invention avoids the high hydrocarbon emissions of early-only injection and the smoke or efficiency losses of late-only injection. The ability to shift the gas ratio allows the engine to behave like a lean-burn spark engine at certain points and a high-torque diesel engine at others, effectively bridging the gap between different combustion regimes through precise electronic timing of the gaseous fuel split.