proper air fuel ratio?

[scottfetsh]

does anyone know proper afr for cng and can it be measured with a wideband o2 or do you need a 5 gas analyzer and how do epa certified kits deal with the o2 signal

[cnghal]

Re: proper air fuel ratio?

Scott,
17.4:1 A/F for CNG as compared to gasoline at 14.7. Most good wideband O2 sensors shouldn't have a problem. Problem usually comes trying to map Lamda signal levels on existing systems.

[MrComment]

Re: proper air fuel ratio?

Thanks cnghal,

Whats the A/F ratio that should be targeted during full load or max power with CNG?

FYI, If you buy a AEM wideband meter, the instructions are wrong since it states CNG A/F ratio should be 14.5:1.

[hachex]

Re: proper air fuel ratio?

17:1 is Correct

[larrycng]

Re: proper air fuel ratio?

Stoichiometric ratios are dependent on Fuel composition -- how much methane along with what-ever else is in the fuel.
If I remember correctly 17:1 is for pure methane. When you get down to around 90% methane your stoichiometric ratio is around 16.3 :1

If your vehicle has a zirconia O2 sensor it will work. They are designed to read oxygen content of the exhaust. (Wide band can do the job.) When you are doing normal switching, averaging about 0.45 volts on your Fluke 88 in record mode you will know the system is in control. Check the fuel trim to know if the system is operating properly plus or minus 10 will work.

If you are using a 5 gas analyzer you'll get closer if it can be set to read methane. Gasoline will generally be close enough.

I would not go richer than 1% CO if the system is not computer controlled, you can overheat the combustion chamber.

Larrycng

[dakudiv]

Re: proper air fuel ratio?

Hi all,
I am an hobbist and i am trying to make a CNG kit controller for my self.'
I have got a kit which i am testing.I would like to know some issues

My kit has a stepper motor i want to know that what all sensors will be used to control the Stepper motor.
I have following sensors.
O2 sensor,Tps,Impulse(RPM).
Please suggest a guide where i can read about this.
Thanks and Regards
dakudiv

[larrycng]

Re: proper air fuel ratio?

Welcome Dakudiv to the site, we try and give you some ideas. First of all, who is the manufacturer of the kit, might help us give you some specifics.

To do the job right you will need to know gas temperature and pressure, this will give a true picture gas density which you will need to know to determine how much air will be need to give a stoichiometric mixture.

You will need to know air density, will need inlet air temperature or manifold air temperature and manifold vacuum. A mass air flow sensor would do the job. Again needed to determine air/fuel ration -- stoichiometry

You also should have engine coolant temperature to help vary the mixture as the engine warms up. You don't need a choke because the you are mixing two gases.

The TPS will help adjust the mix on throttle change if you are using a port fuel injection system. The O2 sensor will take care of fine tuning the A/F mixture.

Any good book on automotive computer systems will give you some of the basic understanding.

Try [email protected] or in the US call 1800-240-1968

Hope this helps

Larrycng

[dakudiv]

Re: proper air fuel ratio?

Dear Sir,
Thank you for your reply.My main aim is to control the A/F value by reading the O2 sensor.I have bought a CNG cylinder and arranged XLP mini motor(Tomasetto cng) and the wiring required and setup required.
The status is that i have a kit installed in my car.

I just have to control the solenoid(CNG inlet),the stepper motor in a closed loop system.
Is there any mathematical Transformation required http://www.freepatentsonline.com/5462037.pdf)
or should i use this algorithm http://www.freepatentsonline.com/5638800.pdf
to control the Stepper motor.

Thanks and Regards
dakudiv

[CptPalmer]

Re: proper air fuel ratio?

So I am a new CNG user and I also have a tuning background. So after reading through this thread I decided to hook my innovate wideband up to my Camry and get some readings. I was shocked to see that I was at 14.4 on idle and cruise. At WOT I am at 12.1 or so. It does not look like Toyota reprogrammed the ECU's at all for CNG. I know that tuning in the Toyota world in a bit tough and piggybacks are usually the best way to go. Might be something to look into as it looks like there is some gas mileage being left on the table.

[2013T]

Re: proper air fuel ratio?

Where can I find a credible source stating the stoichiometric A/F ratio of CNG?

[2013T]

Re: proper air fuel ratio?

I was also wondering if anyone knows where I could find a base engine 12x12 tune for CNG?

[amoparacer]

Re: proper air fuel ratio?

What tuning program,s do the pros use to be able to save stock cals. Edit cals and flash new cals to factory ECU . Dodge, Fords, Chevys .