High Performance Variable Pressure CNG Regulator

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This invention consists of the modification of a Tescom piston sensing CNG regulator to provide a variable pressure output in order to compensate for the limited pulse width response of gaseous injectors that can hinder their metering ability at the upper and lower RPM limits of automotive engines when operated on gaseous fuels. The resulting system, presently installed a car with a 14 to 1 compression 6.6L engine and Holley 950 programmable ECU, allows either gasoline or CNG operation in typical bi-fuel practice. With a constant regulator pressure setting required to meet engine fueling demands at maximum RPM and load, gas injectors frequently are unable to respond to the short ECU driver commanded pulse widths at idle, resulting in over fueling, excess emissions and rough running. Conversely, lowering the gas rail pressure to allow a smooth idle can result in fuel starvation at maximum RPM.

A flexible, dynamic pressure gas injector supply system was constructed utilizing the existing gasoline tank (4) with a variable output electric pump (7) to create a hydraulic servo circuit controlling a modified Tescom CNG regulator (10) through an attached, pressure amplifying “dome load” structure (32) that replaces the function of the regulator’s pressure controlling spring.

This hydraulically actuated “dome load” system consists of a pressure chamber (40) acting upon a piston and integral pushrod (34) within the dome load structure (32) that in turn acts upon the pressure sensing, flow control piston (16) of the attached Tescom CNG regulator (10). The dome load’s pressure chamber (40) communicates with the output of the gasoline fuel pump (7) through a fuel line (9) branching off of line (5) going to the gasoline injectors (28) which are deactivated when operating on CNG. Gasoline fuel lines 5 and 9 are located upstream of a variably restrictive orifice (45) and bypass regulator (47). Dome load piston (34) is actuated here by a variable gasoline servo pressure of between 15 and 40 psi, which is transmitted to the Tescom regulator’s sensing piston (16) to produce an amplified gaseous fuel rail pressure of between 40 and 120 psi. Variable servo pressure is produced by an Aeromotive fuel pump controller (not shown, or ECU 31) which uses input from either RPM or manifold pressure to vary the output flow and pressure of pump 7.

Gasoline servo pressure is amplified by virtue of the larger diameter of dome load piston (34) acting upon the smaller diameter of pressure sensing Tescom piston (16). Higher injector pressures are possible up to the rated output of the Tescom by raising the servo pressure and/ or increasing the diameter of dome load piston (16). Although gasoline/E85 fuel flow and pressure control components were utilized here for the servo pressure circuit, an analogous system utilizing a different hydraulic medium such as windshield washer fluid, (which may also be used for charge air cooling when running on gasoline with high compression ratios optimized for natural gas) is easily conceivable.


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  • Name:
    Anthony Lorts
  • Type of entry:
  • Profession:
  • Anthony's hobbies and activities:
    Car tech, music
  • Anthony is inspired by:
    The challenge of sustainable hi-performance mobility.
  • Patent status: