The Natural Gas VehicleFuel Pressure Regulator

By: Jeff Gotthelf, Engineering Manager

ITT Industries / Conoflow

October 28, 2004

The Functions of a NGV Fuel Pressure Regulator

Reduces CNG pressure from fuel cylinder(s).Inlet from 250 to 3600 psigFactory setting ranges from 30 to 175 psig

Manages gas pressure to engine fuel system.Must respond quickly to changing gas flowMust have very predictable output pressure

throughout range of flow, temperature and tank pressure.Manages varying gas compositions.

Discussion of Joule-Thomson effectRequires heat to prevent icing inside regulatorResists damage from compressor oils

Enable options for pressure sensor, HP and LP gas fittings, relief valve connection, etc.

How Does an NGV Pressure Regulator Work?CONTROL SPRING LOAD

BONNET PRESSURE

PLUG SPRING

DIAPHRAGM

REGULATEDOUTPUT PRESSURE

INLET PRESSURE

GAS FLOW

VALVE SEAT

VALVE

How Does an NGV Pressure Regulator Work?

ITT Conoflow CNG Fuel Pressure Regulator

CONTROL SPRING

DIAPHRAGM

PLUG SPRING

INLET

VALVE

OUTLET

VALVE SEAT

Pressure Regulator Flow Performance

REPRESENTATIVE ITT CONOFLOW HPNGV REGULATORGAS FLOW PERFORMANCE CURVES

90

95

100

105

110

115

120

125

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68Gas Flow Rate

(SCMH)

Out

let P

ress

ure

(Psi

g)

250 Psig Inlet500 Psig Inlet1000 Psig Inlet2000 Psig Inlet3000 Psig Inlet

PRESSURE CHANGE DUE TO CHANGING SUPPLY (10 PSI)

OVERALL PRESSUREWINDOW (16 PSI)

IDLE WOT

Is your regulator’s performance predictable?

Upstream Restriction

NGV FUEL PRESSURE REGULATOR DISCHARGE250 PSIG FUELCYLINDER PRESSUREWITH / WITHOUT SOLENOID VALVE

70

75

80

85

90

95

100

105

110

0 10 20 30 40 50 60 70 80 90 100 110 120

GAS FLOW (LB/HR)

REG

ULA

TOR

OU

TPU

T (P

SIG

)

WITH COMMERCIALLYAVAILABLE DIRECT ACTING SOLENOID

VALVE RESTRICTION

WITHOUT SOLENOID VALVE

Does your regulator get sufficient gas to operate correctly?

Response to Changing Flow RequirementsSudden flow changes (acceleration, deceleration)

How fast does regulator need to respond?

How quickly does the pressure need to recover?

How quickly does regulator need to stabilize?

Do you know what the transient response is for your regulator?

System Cleanliness / Filtration

Upstream filtration required to protect regulator and remainder of fuel system.

Downstream filtration can be used to protect fuel system from excessive compressor oil, moisture or other contaminants.

Metal particulates can damage regulator valve seat and create internal leakage

Is your system protected from debris?

Gas Quality – Effect on Fuel SystemMOISTURE

As CNG expands it gets very cold due to Joule-Thomson effect. Moisture in CNG can form ice and hydrate deposits if the equipment is not designed to handle it.

Standards SAE J1616 and ISO 15403 address permissible moisture in CNG for safe use, but not best performance.

COMPRESSOR OIL

As gas expands and cools, oil dissolved in gas can drop out and load up system. Excessive compressor oils can cause problems to the fuel system.

Joule – Thomson Effect when CNG Expands

ITT Conoflow HPNGV RegulatorTemperature / Pressure data

50 SCMH Flow, 3000 PSIG Inlet(Pipeline Quality Natural Gas)

-80

-60

-40

-20

0

20

40

60

80

100

120

140

8:25:52 8:27:19 8:28:45 8:30:12 8:31:38 8:33:04 8:34:31 8:35:57

Time (hour:minute:second)

CN

G T

emp,

Coo

lant

Te

mp,

Flo

wra

te,

Out

let P

ress

(10

per

di

v)

Outlet Pressure (Psig)

Flow Rate (SCMH)

CNG Inlet Temp (Deg C)

CNG Outlet Temp (Deg C)

Coolant Inlet Temp(Deg C)

Will your regulator still perform correctly when it gets cold?

Symptoms of Freeze Up

Power or smoothness degrades as vehicle is driven.

Vehicle drive ability suffers.

Seems to happen more often during warm weather.

Problem seems to build up, then “fix itself” the next time the vehicle is operated.

Problem is intermittent and difficult to diagnose.

Service shows downstream pressure faults when problem is present, then fault goes away next time vehicle is started.

May be related to different fueling locations.

Does your fuel system show these symptoms?

Managing Joule-Thomson Gas Temperature

Flow bypass to prevent cold gas from freezing against diaphragm

Coolant circulation control to force convection over large surface areas

Engine coolant circulation around critical elements

Can your regulator manage chilled gas flow?

Gas Quality – Compressor Oil Carryover

Example of oil deposits in regulator

Will your regulator and fuel system function with this much oil?

Environmental / Installation ConsiderationsTemperature – Excessive heat can cause leaks.

- Keep regulator away from exhaust system

Shock / Vibration – can reduce product life. - Mount regulator to vehicle chassis, not engine - Mounting brackets must be rigid.

Is your regulator located and mounted properly?

NGV Fuel Pressure Regulator Configurations

Regulator can be configured several ways to meet system needs.Basic model Optional items, such as sensor ports, bias ports, sub-assemblies

Base High-Pressure Natural Gas Vehicle regulator

Regulator customized as an assembly with filter, sensor, and fittings

Conclusion

A robust regulator is an essential component of a safe and reliable NGV fuel system.

It is important to know if the regulator is able to effectively manage NGV fuel system issues such as temperature, vibration, flow changes, supply pressure changes, as well as imperfect gas composition.

For further information, contact me at jeff.gotthelf@itt.com

Thank You!