Fuel Injection
Posted by:
Peter Heid (IP Logged)
Date: February 15, 2002 05:59PM
<HTML>All,
I have been watching with great interest as the burner issue grows here at the forum. The low pressure or vaporizing burner seems to be a strong contender in the field and it appears much research has been completed, and maybe even lost, on this seemingly simple device. I have heard many pros and cons of pressure atomizing burners also and I am glad to see a 12v burner assembly available to the experimenting public. The discussion of on/off versus variable rate burners could also continue for ever, maybe with no clear winner. I think everyone is pretty much headed toward the same goals: clean burning, no residual fuel to smoke upon starting or stopping, adequate heat available to match the system needs through the entire range of operation, fuel efficiency, and low system power consumption as well as other factors such as noise levels and efficient operation in all climates. Another consideration to fuel system development is the SHED (sealed housing emission determination) test all new vehicles must be subjected to. What this does is measures the HC and VOC emissions from a non-running vehicle, and fuel injection, being a sealed system does not add to these emissions. This is a very sensitive and critical test and I have seen BMW motorcycles rejected because the vinyl seat covers were out gassing to much.
Before I proceed, a word of caution for those of us uninitiated in the safety of the system of which I speak.
1) Always wear eye protection when inspecting or working on pressurized fuel systems !
2) Bleed all pressurized fuel systems as per manufacturer instructions !
3) Never touch an automotive or other high amp battery terminal when wearing any metal !
Now back to the fun. The crazy thought I want to share today comes from my old world, the IC world. Imagine if you will, remember I am imagining this also, the use of a mechanical or electronic fuel injection system to control the fuel/air ratio feeding the burner. The bosch “K” mechanical injection system was my top contender in the field. The K system has been in use for over 30 years with few limitations and little refinement necessary on Volvos, VWs, Saabs and others. The system uses a throttle plate that measures air flow and varies the fuel rate directly by moving a metering needle in the fuel distributor. The metering needle uncovers laser cut slots, for exactly equal proportioning, that feed each injector. The throttle plate is dampened by piston/cylinder assembly fed by a pressure regulated control circuit the fuel distributor. The injectors in this system are opened by the fuel pressure, so if no air were flowing, the metering needle would block the flow to the injectors preventing them from operating. When off, there is no drip or leakage and when pressure is available to open the injector, the pressure is also adequate for the complete atomization of the fuel allowing start stop operation with very little unburnt fuel. The damping circuit has a warmup pressure regulator in the line to allow changes in the fuel air ratio during times of cold engine operation on the IC engine. The control pressure regulators on some autos includes an electric heater to speed the warmup of the regulator beyond the rate provided by the heat of exterior of the engine.
I see no reason why the original injectors as well as most of the Bosch system can’t be retained for use in the construction of a steam burner/boiler. The fuel flow rates can go from about 2MPG to above 30MPG on autos with IC engines which should be satisfactory for most steam applications. I have been quite set on the on/off type of burner for my use because it is hard to vary the fire box size to match the fuel burnt for maximum efficiency but this system could be used as a variable system as designed, an on/off system, or even operated in steps depending on the number of installed injectors (from a 4 or 6 cyl) that you feed with fuel. The warmup or control pressure regulator could easily be used to switch from one fuel to another by varying the temperature because this changes the control pressure which directly alters the air fuel ratio.
For very fine adjustments, the Bosch K system uses a feed back loop (lambda sonde I think it is called) in the control pressure circuit on versions produced from about 1979 on. The exhaust gas components are measured by an oxygen sensor that provides a tiny electrical potential to a computer which in turn regulates the control pressure by varying the duty cycle of a 12V solenoid valve in the control circuit. This is a super fine adjustment, if you were to unplug the oxygen sensor while a car is running and with one hand, touch the wire leading to the computer from the sensor, and with the other hand, touch the positive battery terminal, the fuel air ratio will go to richest point in the closed loop. Touch the negative terminal instead and it goes to the leanest point allowed by the loop and at an idle you can just hear the difference between the two points. If the closed loop was used, a failure of the that portion of the system such as the computer or frequency valve, would not impair or disable the vehicle except to increase the emissions.
This system does an excellent job of controlling air fuel ratios and is considered clean burning by today’s emission standards and the main causes of failure are dirt or water that remains in the fuel long enough to cause corrosion. The main reasons the K system are no longer specified on new cars involves the slight air flow restriction and slightly slow action of the throttle plate and the fact that the injectors are constantly firing into the manifold unlike the timed, cylinder injection of the newer electronic Bosch L system. Both issues don’t seem to be a concern when using the system to fire a burner but that doesn’t mean the newer electronic systems can not be used also.
The servicing of the K system involves few tools which include a pressure gauge to check injection & control pressure as well as leak down, a dwell meter to check the duty cycle of the frequency valve, a tiny allen wrench (2mm I think) to adjust the basic position of the metering needle in relation to the throttle plate, and a volt ohm meter completes the package of special tools needed. Several manuals are available on the various injection systems from companies like Haynes or Clymer and bosch produces their own work shop manuals also.
The fuel pump on most injected autos is in the fuel tank and it can be an expensive item to replace and since they use the fuel for lubrication and coolant, they don’t tolerate many dry runs or water corrosion. Of course the pumps are of electric in operation and although the power consumption is low, any device that adds to the overall power consumption of the vehicle can not be over looked. The volume and pressure required can be provided by an oil burner pump such as the sunstrand if the electric pump won’t fit the proposed design.
In conclusion (finally) I think this technology has the five abilities I most desperately desire in parts I choose for my system design, Availability, Affordability, Adaptability, Adjustability and Dependability.
Sorry I drag these things out so much
Peter Heid</HTML>