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One of the main challenges with using a pintle injector for a nitrous-ethanol combo is spray angle. A lower spray angle is desirable because it means the mixed propellant has to travel further to reach the wall, and so can disperse more. However, when using nitrous-ethanol as propellants, a high mixture ratio is often used. This means that the nitrous will have a lot more momentum than the ethanol, and since the pintle is ox-centered (there is basically no way to manifold the regen cooling to the center of the injector to have it be fuel centered) the spray angle will be exceedingly high. However, we intend on drilling the pintle holes at an angle to enforce a lower spray angle.
This is the current iteration of the pintle injector, with some dimensions (i.e. number of film cooling holes or number of flange bolts) not calculated yet. Also, the nitrous orifices are not angled yet. However, the final design will most likely closely resemble this, as it is machinable and contains no interpropellant seals.
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