OK, so now this is looking interesting depending on the amount of He3 in the Helium!
Doing the economics of He3, it is plausible that, given the price of He3 during Papp's original work, Papp's secret ingredient in his fuel was pure He3. (The natural occurrence of He3 in Helium gas isn't even close to the energy density required to run the demonstrations.)
However, He3 has recently auctioned for $2000/liter.
Given that price for He3, the economics of He3 don't look good even including completion of burn-up via p+B11 => 3He4 as reported by John Rohner:
He3+2*He4+p => 3*He4 + 0.0212523u
where p stands for 'protium' or H1
3.0160293+2*4.002602+1.007825-3*4.002602 = 0.0212523
In other words, if you take 12grams of a gas that is 3gm of He3, 8gm of He4 and 1gm of p, and burn it through the entire cycle of Be7=>C11=>B11=>He you'll get:
0.0212523g*c^2?kWh
(0.0212523 * gramm) * (speed_of_light^2) ? kilo*Wh
= 530571.01 kWh
To get that much energy we had to purchase 3gm of He3 at $2000/liter:
3g/530571.01 kWh;.17g/l;2000dollar/l?dollar/kWh
([{3 * gramm} / {530571.01 * (kilo*Wh)}] * [{0.17 * gramm} / liter]^-1) * ([2000 * dollar] / liter) ? dollar / (kilo*Wh)
= 0.066521007 dollar/kWh
Although a fuel price of 7 cents per kWh output isn't outlandishly high for electricity, it certainly isn't nearly as cheap as what you can achieve by simply adding p and B11 directly to the chamber.
Moreover, I haven't done the coulomb barrier calculations on the B11 nucleosynthesis -- so even though it may be quite feasible within some stellar cores, it isn't clear it could be achieved in a Papp engine plasmoid.