Liquid Phase LPG Injector Calibration 2

[BogRob]

Gentlemen,

Would anyone be able to share a method to measure actual injector pulse width (msec) vs volume flow at a fixed fuel pressure for a liquid phase (lp) LPG injector?

I have come across eight Siemens LP LPG injectors used in the Icom JTG systems which I am planning to use in my own application. The rationale behind not simply using one of their systems is I can see many shortcomings where fuel composition and density are not accounted for, nor am I over the moon about any ‘interceptor’ style engine management.

I hope to learn a lot during this project except for it to begin I either need the data for these injectors or to measure it myself. My current ideas to measure the data are as follows:

1. Using a bottle of N2 to regulate the fuel pressure of the LPG, systematically cycle the injector (with nozzle to atmosphere) at various fuel pressures and supply voltages whilst recording the mass lost from the LPG and N2 containers by means of scales.
The preconceived flaws in this system are the unavailability of a scale that would be able to accurately weigh both containers with resolution to capture the mass loss rate. Mass of fuel loss would also be needed to convert into volume loss rate.

2. Similar process to number one; however in this instance the LPG would be captured into a sealed pressure capable vessel of known volume. Based on the temperature and pressure of the fluid and the known volume, the liquid volume could be calculated.
Again the inherent flaws in the process would be that the N2 pressure regulator would need to compensate for the decrease in pressure differential as the capture vessel pressure increases. The volume of the reference line would need to be accounted for.

3. Use a test fluid that is liquid at room temperature and directly measure the liquid volume whilst cycling the injector as in process one.

I am in favour of process three; however I am unaware of a suitable test fluid which either shares strong physical characteristics of Liquid Phase LPG or that can has known correlation factors to correct the collected data so that it represents injection of Liquid Phase LPG.
I look forward to all future responses and thank you in advance.

Regards,

Robert Flynn
Mech Eng (Hons)

 

[teknix101]

With a Harley badge! 8^)

 

[teknix101]

129931 was a thread a while ago that went into quite some depth where I contributed an idea or two as did Franz and Turbo and others - worth the read Rob
Cheers

 

[BogRob]

Turbo:

I was fortunate to read an SAE paper of yours yesterday: The Effects of Fuel Composition, System Design, and Operating Condition on In-System Vaporization and Hot Start of a Liquid-Phase LPG Injection System.

In addition to the above paper I came across a few of your patents, of particular interest was Patent Number; 6341597 B1 Fuel Injection System For High Vapor Pressure Liquid Fuel.

Upon seeing the PT diagram on page 5 of the SAE paper, all subsequent discussion points seemed extremely logical. The PT diagram is a very succinct visual aid to display the issues of a liquid phase injection system, your earlier points referring readers to refrigeration cycles is spot on. I found the discussion on hot start interesting and was glad that the the analysis acknowledged common pump pressure vs flow characteristics in its inclusions. One can appreciate the use of Nylon 66 GF 30/60 as a desirable material to construct a fuel rial as it has a similar tensile strength to 60601-T4, however the coefficient of thermal conductivity is approximately 925 multiples less and the specific heat is 1.7 multiples greater. Furthermore, a change in fuel composition as the liquid faction percentage varies i.e is consumed by the engine is a topic I have never come across.

I would appreciate if you would comment on a few of my following thoughts:

The variables that a LPi system engineer can control generally relate to the thermal management of the system, efforts are directed to ensure that the fuel remains at a minimum saturated liquid in the delivery system. This challenge is most evident during hot starts where factors such as fuel temperature will lengthen the time period before the the engine can be started due fuel density. In order to minimise heat transfer to the fuel tank the engineer could use a return less system where the fuel pressure regulator is located within the tank. The engineer would, however, have to account for the upstream pressure loss when deciding upon the boost pressure so that the fuel remains at a minimum saturated liquid. A return line could also be included in the system with a solenoid bypass to decrease hot start times.

Turbo, have you also had any experience with the 'anti icing nozzles' implemented by Vialle and Continental? Are these absolutely necessary or is it possible to treat the injector much the same as any other gasoline injector with no tip extension?

Finally, the top o-ring(FVMQ?) does not appear to be dimensionally standard, would you share the recommended port sealing diameter? My educated guess expects that the ID should be 0.976", however, because of the of flash on the injector top 0.980" would be more appropriate. From a tooling perspective 0.984" or 25.00mm would be ideal. For the lower o-ring(FKM?) I would expect a ID of 0.516" or 33/64".

Your input is extremely appreciated.

Rob

 

[patprimmer]

I just saw mention of GF Nylon for fuel rails.

While it is a material with some outstanding properties I would issue several cautions to be taken into consideration with its use.

It loses a considerable amount of flex mod and some tensile but gains elongation on absorption of water from the atmosphere. Amount absorbed depends on the RH and time to equilibrium depends on section thickness and temperature. Nylon really has a high affinity for water, but a very slow diffusion rate. It also swells somewhat as it absorbs water. Of course the higher the glass content, the less the effect.

Any glass fibre reinforced plastic is quite anisotropic and the glass fibres tend to line up in direction of flow when moulding. The along and across the flow properties can be quite different.

There can be substantial differences between parts machined from extruded bar stock and an injection moulded part due to:-

1) The direction of flow will be different and therefore glass orientation may be very different with the consequential effect on properties of the part.
2) Plastics are very notch sensitive, although fibre reinforcement mitigates that to some extent. This means machined parts have notches acting as stress risers.
3) Extruded bar-stock is made from very high molecular weight polymer when compared to injection moulding grades. This greatly increases impact strength and elongation at break.

In a nutshell, what I am saying is GF nylon could well be very suitable, but care needs to be taken as prototypes WILL perform differently to production parts.

Regards
Pat
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[BogRob]

Hi Pat,

Thanks for the feedback, I can appreciate everything you've stated. As with all fibre reinforced composites, material properties are highly dependent on fibre direction, length and dispersion. I guess my suggesting of GRP Nylon was a nod towards current industry where this material is used for LPi fuel rail manufacture.

Thanks for the information!

Rob