Meth Injection - PWM Calcs for Injector - Calcs within, request check

[ktm]

I am installing meth injection on the car and want to use Wolf to control the HSV. I am going to us FJO racing HSV on my car.

 

Saying that, I need to calculate the duty cycle of the HSV for a given MAP and RPM, based on my injector PW, injector flow rate, and HSV flow rate at various pressures.

 

Following are the calcs. Someone PLEASE review and add to the discussion.

 

First, you need your IPW table from your standalone (Hydra, Wolf, Microtech, etc). This gives you your injector pulse width in milliseconds.

Next, take the rated flow rate of your injector and convert it to a MASS flow rate. I am using 7MGTE injectors bench flowed at 500 cc/min. Gasoline has a density of 737.22 kg/cu m. which is equivalent to 0.73722 g/cc. I converted the time to milliseconds for everything as well since the IPW is in milliseconds.

 

Thus, my MASS flow rate for my injector is:

500 cc/min * 1 min/60 sec * 1 sec/1000ms * 0.73722 g/cc = 0.006144 g/ms

 

Using an example IWP, my MASS of gasoline for a given IWP is

10 ms (IWP) * 0.006144 g/ms = 0.06144 grams of gasoline

 

I keep saying MASS flow rate because the ratios (AFR, etc.) are all MASS based and not VOLUME based.

 

Next, you need to calculate your MASS flow rate of methanol or 50/50 based on your fuel MASS flow rate. This will be specific to your mixture. Assuming a 50/50 mix, your density will be (1000 kg/cu + 791.30 kg/cu m)/2 = 895.65 kg/cu m or 0.89565 g/cc.

 

Now that you have your density of mix, determine HOW much of the mix you need for ONE COMPLETE ENGINE CYCLE. This is TWO revolutions of the engine. Therefore, for my car which has an inline 6, I multiply the mass of fuel used for one injector pulse width by 6 and assuming a 40% methanol injection rate

 

0.06144 grams * 6 = 0.3686 * 0.40 grams = 0.147 grams 50/50 mix

 

Your meth injector flow rate must now be converted to mass flow rate like the fuel injector. HOWEVER, remember that you need to take into account your MAP as it will reduce the flow pressure from the pump (which is why we have vacuum referenced FPRs unlike the meth pump). Therefore, you need to calculate your new injector flow rate based on the revised MAPs as follows

 

square root (new pressure/old pressure) * flow rate

 

My injector will flow 700 cc/min at 150 psi. My new flow rates are as follows

 

Below is a line taken out of my spreadsheet

MAP FP New Pressre New Flow Rate

2.18 147.82 (150 - 2.18) 694.8 cc/min 0.0103 g/ms

 

Now that I have a mass flow rate required, I can calculate the HSV pulse width required:

 

0.147 grams / 0.0103 g/ms = 14.3 ms

 

However, PWM HSVs do not operate like a typical fuel injector. You must specify a duty cycle for the PWM control. This is where I was stumped until my Guiness inspired epiphany (I hope).

 

Remember that it takes TWO complete revolutions of the engine for ONE complete combustion cycle for all cylinders. Therefore, at 3000 rpm or 50 revs per second, 25 CYCLES per second are completed. Take the inverse of this and convert to milliseconds and you get 40 ms per cycle.

 

Ta da! Now, the HSV injector duty cycle is simply

 

14.3 ms / 40 ms = 36%

 

Is this correct?

[jeffp]

Now that is some calculating! I have the FJO injection kit on my car. I am running two of their 900 cc Injectors.

You are going to try standard injectors? You will not be able to pressurize the standard injector to 150psi I do believe you will damage even the bosch sytle injectors with that much pressure.

I was running my car on the one 900 cc injector. The car really liked it, but it was not enough methanol.

The FJO controller has a standard map 16 X 16 blocks to tune, all based on RPM and engine vacuum.

Have fun with it, you will like running methanol.

[dr_hunt]

I was just wondering why you would want to add water to methanol? Seems to me that you'd just want straight methanol.

 

Your forgetting that you can add alot of methanol, it is quite unlike gasoline even as a detonation inhibitor. I think you'll find that the more you add the better it works up to a certain point. Two 900cc injectors would seem about right IMO.

[ktm]

Jeff, I will be running FJO's 700cc injector. You are making quite a bit more power than I am so I hope the 700cc injector will be fine. Their website claims it is good up to 500 crank hp, and I will be hopefully producing around 425 crank once I am done. I will be using Wolf to drive the injector via a PWM channel, hence the calcs. I have determined how much methanol I need to inject, I just needed to determine the duty cycle of the injector. I know that I really need to just setup it up and test it, but the calcs at least get me in the ball park.

 

Dr Hunt, everything I have read so far regarding meth injection is to run a 50/50 mix. The meth provides good detonation resistance and the water cools the charge.

[Bernardd]

Jeff needs more because he's also running 100% meth. I picked up 4mph and .5sec et when I switched from 50/50 at the same boost level. Have you checked out turbobuick.com? Best methanol forum that I've found on the net.

[dr_hunt]

Where is this meth injector located in the system typically?

[Bernardd]

A couple of inches before the throttle body in the intake piping.

[Bernardd]

Bo, this injector is methanol compatible according to the vendor. It might be easier for you to setup using a couple of these.

 

Link: http://store.summitracing.com/partdetail.asp?autofilter=1&part=TFS%2D89120%2D1&N=700+4294925239+4294839074+4294870762+4294891681+4294748911+115&autoview=sku