Reid Vapor Pressure TESTING!

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link: http://www.dynotechresearch.com/blog/archives_cat.asp?cat=7

Reid Vapor Pressure TESTING!

 
 For  race engine tuning, our biggest problem is stale race gas that racers  buy unwittingly. Stale race gas can have excellent octane, but  volatility can be poor due to the absence of important “light ends” of  the fuel. Light ends are the first to escape into the  atmosphere—creating that satisfying “whoosh” when sealed drums of race  gas are first opened. But after gas is drawn and drum resealed, more  light ends will escape into the air pocket above the fuel in the  resealed drum. Then when the drum is opened again to draw more fuel,  there is another, but less satisfying “whoosh” and more light ends  escape into the atmosphere. By the time that large drum is consumed a  few gallons at a time, no more “whoosh” is heard. Then the fuel is, for  our purposes, “dead”. With the light ends that help initiate  vaporization gone—escaped into the atmosphere—the fuel then needs  excessive amounts of heat to get it to vaporize. Its volatility is now  poor, and trouble is lurking for those who don’t understand what’s  happening. I like to compare race gas’ “light ends” to the CO2  carbonation in 2 liter bottles of Coke. When first opened, the Coke is  fizzy and good. But every time the plastic bottle is resealed then  reopened later, more CO2 escapes into the atmosphere. And each time that  happens, the fizz is diminished. After being opened and resealed a  dozen times, that last swig of Coke you take from the bottom of the  large bottle is awful—flat and fizzless, just like stale race gas.
 
 What  about those "sealed" 5 gallon “pails” of race gas? Are they filled and  sealed at the refinery, or are they transfilled from open drums at a  wholesaler’s facility and then “sealed”?? How long has that drum  remained open? It pays to be leery!
 
 Carl  McQuillen Racing Engines in LeRoy, NY continues to manufacture and sell  nitrogen pressurizing systems for drummed race gas. Those are a great  tool for dispensing and storing race gas in 30-50 gallon drums, very  much like draft beer systems do with CO2.
 
 Poor  volatility from escaped “light ends” can result in fuel failing to  vaporize as it travels from the carbs/ throttle bodies into the intake  ports/ crankcases (two-stroke)/ combustion chambers. We accurately  measure our engines’ fuel flow as it travels from the fuel pumps into  the engines, and we expect to see close to .60 lb/ hr of fuel for every  HP the engine is generating. When practical, we measure airflow into the  engines’ airboxes and .60 lb/hphr is typically 12/1 A/F ratio (12  pounds of air per pound of fuel). As a secondary source if information,  we use an Innovate wide band A/F ratio meter that measures the exhaust  gases coming out the pipes and gives us a chemical A/F reading that  often is identical to the mechanical readings. As we approach maximum HP  at 13/1 A/F, if octane is insufficient, we sometimes hear loud “clicks”  of detonation on our copper tube sensor, and can abort testing before  damage occurs. But stale gas measures pound for pound exactly like fresh  gas, and what if only ¾ of the fuel is vaporizing in the combustion  chamber? That means our indicated .60 lb/hphr is actually, net in the  combustion chamber, .45 lb/hphr and that dandy 12/1 indicated A/F is,  net, 16/1. In that situation, there might be zero clicks of deto, just  wickedly net lean mixtures that cause pistons to grow quickly and stick  in the cylinder bores! Our dyno flowmeters are indicating that all is  perfect, but what it doesn’t tell us is the % of fuel vaporizing and  burning in the combustion chamber vs. the % that finally manages to  vaporize and burn in the hot pipes. If the gas is stale, all of our dyno  meters can be telling us all is well, zero clicks of deto means octane  is sufficient, and piston(s) can stick and spoil our tuning session.  There’s nothing worse than a guy with a “stuck” engine having to have to  pay for dyno time, take it home to fix it, then come back to retune  with fresh gas and pay again.
 
 
 
 My  most recent obvious stale gas experience was my pal Gene Hurin (who’s  been tuning here with his jet-changing wife Cathy for 25 years) coming  here with a new HTG Polaris 1000 improver. He had bought 5 gallons of VP  C16 gas from a local vendor, and Gene knew it came from an unsealed 55  gallon drum in the corner of the warehouse. Gene and I talked about the  issues of stale gas before we began tweaking the Lectron carbs, but when  we got down to ¾ turn on the power jets the engine seized with no  warning at .60 BSFC and160 lb/hr  of fuel flowing into the engine with 100 degree F coolant! Cringe. So  Gene went home, fixed the engine, then came back again with Sunoco  Maximal he bought from the infamous “Fat Nancy’s” in Pulaski NY who  sells a zillion gallons of Sunoco race gas, and fresh is what Gene  bought. This time with Gene’s orifice puckered severely, we leaned it  down to 160 lb/hr, then continued leaning down all the way to 140 lb/hr  and the engine was happy and powerful! It was much more pleasant  charging Gene for the second tuning session.
 
 How can we prevent future issues like this?
 
 Kevin Cameron suggested that the important “light ends” of the fuel contribute substantially to Reid Vapor Pressure. Every  name brand race gas has an RVP rating. That being the case, why not  test dyno customers’ race gas for RVP before we wreck parts? What is  RVP? How is an RVP test performed?
 
 Thank  you KC and Google! RVP is determined by precisely heating a quantity of  gasoline to 100.0 degrees F + or - .2 degrees F. Then after agitating  the 100.0F fuel, the pressure in a closed air chamber above the gasoline  (4x the volume of the gasoline) is measured with an accurate bourdon  tube test gauge and that is the exact RVP. The higher the RVP, the  easier it is to vaporize, especially in cold winter air. Winter blended  pump gas RVP is close to 15psi. Amond the lowest RVP even when fresh is  C16 with less than 2psi! Trying to start a C16-fueled engine in February  is impossible! Sunoco Maximal which has octane similar to C16 has 6psi  RVP--a much better high octane fuel for cool engine performance in  winter air.
 
 If  you watch dragracers "clean out" their engines on jackstands prior to  the start of a race, you often hear them gurgle and pop for the first  few quick blasts from clutch engagement to peak RPM. That gurgling you  hear is lean misfire from cold low RVP gas going through cold carbs and  into cold combustion chambers. Once the combustion chambers are heated,  more of the lava-lamp-like globs of fuel will finally vaporize, and the  engine will run cleanly. The higher the fuel's RVP, the better!

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So  let's just measure our fuel's RVP. Sounds simple enough, but when I  found that the equipment needed to do this cost $7000—a $6000 precision  water heater and a $1000 vessel for containing and measuring the fuel  head pressure, I went to Ebay. There, I found an engine manufacturer’s  surplus Koehler water bath used to precisely heat the fuel samples to  100.0F. Who in the world, but me, would want to buy a used RVP test  bath? So it had languished on Ebay with zero bids since August, and I  came along and “bought it now” for 20% of new cost. But it came with no  fuel testing vessel—called a RVP “bomb” made of stainless steel,  hydro-tested to 1000psi and a lab certified pressure gauge. I had to  bite the bullet and buy a new fuel test “bomb” (yes, that’s what they  call them!) from Koehler for $700, and a new $400 15psi .25% accuracy  pressure gauge was Ebayed for $30. So now we can test for stale  gas—hopefully before we wreck parts!
 
 I  hated high school chemistry. The only enjoyment I got from those awful  lab sessions was making hydrogen bombs from dissociating hydrogen and  oxygen from water then igniting those with a match.. Acetylene bombs  were also great fun, especially when several of my equally deviant pals  and I pooled our precisely rationed grams of calcium carbide to mix with  water! But here I am, trying to figure out the Reid Vapor (Vapour)  Pressure of racing gasoline! My annoyed chemistry teacher would be  proud, if he were still alive.
 
 An  RVP test takes about an hour—about as much time as it takes to set up a  sled or bare engine onto the dyno. So from here on, RVP testing can be  done prior to race gas dyno testing/ tuning, so the one final mysterious  variable might be eliminated.
 
 
  Koehler RVP “Bomb”. The  gasoline to be tested is poured into the shorter lower portion of the  stainless steel cylinder, which unscrews from the hollow upped air  chamber. After the lower chamber is filled with gasoline to be tested,  it is attached to the upper chamber.
 
  Here’s the RVP bomb  sitting in the Koehler circulating water bath at 100.0F. It holds about  20 gallons of 100.0F water agitated by a propeller driven by the motor  on the upper right.
 
 The yellow temperature  numbers are thermostat setting, and the red temperature numbers are the  exact temperature of the water circulating around the “bomb”. Precision  is required!