Bi-fuel control system and retrofit assembly for diesel engines

What is this patent about?

’395 is related to the field of bi-fuel conversion systems for industrial diesel engines and electric power generators. Traditionally, these high-capacity engines rely exclusively on diesel fuel, which is costly and produces significant emissions. The invention provides a retrofit assembly that allows a conventional reciprocating diesel engine to operate on a mixture of methane-based gas and diesel fuel without requiring permanent internal engine modifications or sacrificing the reliability of the original diesel governor system.

The underlying idea behind ’395 is that a diesel engine can be made to consume significantly less diesel fuel by introducing a homogeneous air-gas mixture into the intake manifold, effectively tricking the engine's mechanical or electronic governor. Because the gas provides a portion of the energy required to meet the engine's load, the governor naturally senses a decrease in demand and reduces the diesel injection rate. This creates a seamless transition between fuel modes that maintains constant power output and efficiency by using intake manifold air pressure (MAP) as the primary proxy for engine load.

The claims of ’395 focus on a digital control architecture that regulates gas flow through an electrically operated throttle body positioned downstream of a positive pressure regulator. The system is defined by its ability to monitor real-time engine load—specifically through MAP sensors or kilowatt output indicators—and adjust the gas control valve to a plurality of partially open positions. This ensures that the gas-to-diesel ratio, which typically ranges from 40% to 90% gas, is optimized across the entire operating spectrum of the engine.

In practice, the system utilizes an air-gas mixing device that avoids the use of a traditional air throttling plate, thereby preventing pumping losses that would otherwise degrade engine efficiency. An Electronic Control Module (ECM) manages the safety and logic of the system, monitoring for critical faults such as low gas supply pressure or excessive engine vibration. If a fault is detected, the system automatically closes a solenoid valve to cut off the gas supply, allowing the engine to revert to 100% diesel operation instantaneously and without a drop in power.

This approach differentiates itself from prior art by offering a non-restrictive retrofit that preserves the engine's original airflow characteristics while providing sophisticated data logging and programmable safety set-points. Unlike dedicated spark-ignited gas engines, this system retains the compression-ignition reliability of the diesel cycle. By mapping gas flow to specific manifold pressure levels, the invention achieves a precise load-following capability that allows large-scale generators to parallel with utility grids or other units without the instability typically associated with alternative fuel mixtures.