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Air starter

  1. Mar 10, 2017 #1
    Hi I'm very new to this so bear with me lol. I'm trying to plan out a project for building a diesel powered car and I want to use an of the shelf pneumatic starter for novelty but I don't know how much volume I need. So the starter requires 120 psi @500scfm. My idea is to use scuba tanks or aerospace gas accumulator spheres which are rated at 3000 or more psi and regulate that down to what I need as far as pressure. From what I understand those starters can have either 3/4" or 1" inlets ( I don't know if that matters) that's pretty much as far as I got before I realized I need help. Any help would be much appreciated thanks!
  2. jcsd
  3. Mar 10, 2017 #2


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    Welcome to PF.

    It would certainly be a novelty.
    What make and model of starter.
    The mass of the tanks, control gear and pneumatic starter will be greater than the electric starter motor and battery you are throwing out.
    Build the car first with space to spare, then look at making it much more complex by going for a pneumatic starter.
  4. Mar 10, 2017 #3
    Interesting. I know nothing about pneumatic starters but where and how it would be integrated in to the ECU should be an enjoyable challenge. What are the benefits of going pneumatic?

    Are you really throwing the battery out? That raises a lot of questions.
  5. Mar 24, 2017 #4
    Pneumatic starting is routinely used for large diesel engines. Many years ago, I worked for a large supplier of diesel engines and engine driven equipment. Many of our products used large air flasks, pressurized to a few thousand psi, as I recall, to drive air motors to start the engines. It is definitely a well established technology, so I suggest a bit of internet research.
  6. Mar 25, 2017 #5


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    In the past semi tractors used pneumatic starters. I believe in the Mad Max movie The Road Warrior the semi tractor had a pneumatic starter. Nothing new here really. As far as tying into the ECU I cannot imagine the need to do so. The OP may not even intend to use a diesel engine that requires an ECU or even a battery for that matter. In the past if diesel equipment had enough charge in the battery to start the engine that was all that mattered. If the charging system wasn't working or even non-existent it simply wasn't an issue unless the engine was stopped and there was not enough left in the battery to restart.
  7. Mar 25, 2017 #6


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    I agree.

    It matters little how a diesel is started, it just has to be reliable. Where the diesel is on a transport vehicle it may also need a system with a low total mass as that maximises payload, acceleration and the efficiency of operation.

    Many small diesels have an electric starter because it is simple. Bigger diesels may use a pneumatic starter motor and share the reservoir with pneumatic auxiliaries such as brake servos and gear change controls.

    There were also hand cranked SI donkey engines used to start bigger diesels on earth moving machinery, along with diesels that were electrically started as SI engines on gasoline, but then the same engine switched to diesel operation on heavy fuel oil or whatever was available.

    When a battery died, or a pneumatic reservoir lost pressure, there needed to be a way to recover from the situation. That added complexity and weight. For a small diesel in a hybrid vehicle today, an electric starter would be most convenient as it could conveniently self-start when it needed peak power, (to perform a flanking manoeuvre), or to charge the battery. Solar panels could also maintain charge in the batteries.

    A pneumatic starter on a small diesel in a hybrid vehicle would probably not be an advantage unless the vehicle was a pneumatic-diesel hybrid that stored significant energy in a pneumatic reservoir rather than in an electric battery.
  8. Mar 25, 2017 #7
    I have an 80 cubic foot scuba tank. That'll run your 500 CFM starter for about 9 seconds.
  9. Mar 25, 2017 #8


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    How much does the tank weigh. How much would the compressor and air drier weigh?
  10. Mar 25, 2017 #9
    The apparatus at the dive shop is about the size of a small cargo van, and it takes a while to fill up.
  11. Mar 27, 2017 #10
    Wow, the OP hasn't been back but what does that matter? This is the OP's statement:

    Then these statements were added:

    It may have been wrong of me to think the OP meant car when he said car and for me that suggests a planned use. Had the OP said "experimental vehicle," I probably would not have wrote what I did. He did say car though and implicit with car comes laws and licensing.

    I can't say every state has a statute like this one from Wisconsin but most have minimum requirements at least that state something along the lines of, "For a vehicle to be awarded a VIN, titled and licensed it must at least meet the minimum design standards as set for by the SAE for the year previous to the year of application."

    Updated 2015−16 Wis. Stats. Published and certified under s. 35.18, Chapter 347
    (1) The headlamp shall be an electric headlamp and the current shall be supplied by a wet battery and electric generator, by a current generating coil incorporated into the magneto or by a generator driven directly by the motor by means of gears, friction wheel, chain or belt.


    A battery is required. It's a safety and margin of safety requirement which for a battery is one in the same.

    I'm not really sure of what to think of this except when is anything ever needed until it is? I can agree with you if that was your point? Even with disregarding the battery has already been hypothetically thrown out.

    About the ECU, I admit I haven't had a reason to stay up on governing requirements but as of Jan 1, 2015, they were to be required in all road vehicles sold in the US and additionally more vehicles such as farm tractors and all the job specific vehicles seen at an airport. I think the regulation was passed in 2012 or 13, and at that time something like 97% of all vehicles sold in the US already had self monitoring and feedback devices so the regulation wasn't about getting black boxes in to vehicles. The regulation is about not legally taking them out. The regulation was generically referred to as MAP-21. MAP-21 is name the NHTSA had given to the Event Data Recorder (EDR) standardized protocols it was developing.

    Maybe I shouldn't have taken the OP literally? I admit I've made that mistake before.
  12. Mar 27, 2017 #11


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    As far as dates and model years go, it is irrelevan in most places. If i take a vehicle with a good VIN made the in the 50s then all it needs to pass is emissions for that year. I can modify it all I want as long as it is road worthy to the specs of its year of manufacture.
  13. Mar 27, 2017 #12
    OK. Once again I thought he was building a car. I understand now he's only modifying one.
  14. Mar 27, 2017 #13


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    Well I don't think we really know for sure what he is doing. I was just giving an example.
  15. Apr 4, 2017 #14
    The central topic in the OP was regarding how much volume he needed for his air tank. He was not asking for clarification on legal requirements in certain jurisdictions for certain applications. We can't speculate that he is planning to drive this on public roads or any other application. No reason to believe he is doing anything wrong here.

    OP, how long does it generally take to start your engine? If you could tell us the minimum and maximum seconds of cranking before starting, it would help calculate an appropriately sized air tank. I'm assuming the starter requires 120PSI at the inlet orifice. Correct? Can you specify at which point in the flow path it is that you need there to be 120PSI? Your idea to use a pressure regulator and an airtank well above 120PSI is wise and should work well. You will want to use a regulator that can keep 120PSI at your volumetric flow rate demands.
  16. Apr 5, 2017 #15
    For the OP, you stated you want something "off the shelf." A traditional air starter such as used in small diesel engines is a gear reduction device that is driven by a compressed air turbine. These use a large amount of air, produce a moderate amount of starting effort and are economical " off the shelf." If you move to the medium of large diesel world an air start engine uses air injected directly into the cylinder via a sequenced controller to force the engine to move. This style uses a small amount of air, produces a large amount of starting effort and is complex "off the shelf."
    If you are strictly looking for the novelty factor I would stay away from air start. It has merits if you are running an engine that requires large effort. Air start also requires increased parasitic losses (small compressors are typically less efficient than alternators) to recharge prior to the next start.
  17. Apr 5, 2017 #16
    The OP has never been back so addressing peripheral issues as they are brought isn't interfering with the OP's question. That aside, the OP's question was answered. Directly with a number like you've done? No. Where the OP can go to find the standards to the question, yes. In the US the competent authority for the question is the SAE. Why assume what the OP needs when the minimum standards are readily available? The standards are available in the form of both standards alone and standards with supporting engineering data. Considering the extent of the knowledge you've demonstrated I assumed you had been through the process of documenting the standards of conformity.
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