BIPROPELLANT PERFORMANCE OF N2H4/MMH MIXED FUEL IN A REGENERATIVELY COOLED ENGINE

Experimental regeneratively cooled bipropellant engines, with a vacuum thrust of 2000 N at a chamber pressure of 0.98 MPa and an area ratio of 240:1, were fired with hydrazine-monomethyl hydrazine (MMH) mixed fuels to evaluate potential performance and cooling improvement. Regeneratively cooled engine tests were conducted with 80% hydrazine-20% MMH mixed fuels, as well as with MMH single fuel, utilizing optimized injectors for each fuel. The chamber pressure was varied in a range from 0.6 to 0.9 MPa. Long-duration firing tests of 160 s were conducted to evaluate heat soak-back level and to demonstrate safe shutdowns of a mixed fuel regeneratively cooled engine. The peak specific impulse of the mixed fuel was more than 322 s, while that of MMH fuel was 308 s. Regenerative cooling with the mixed fuel seemed to be particularly advantageous in that the temperature increase through the cooling channels was smaller than that of MMH fuel; this reduced performance degradation due to reactive stream separation (''blow apart'') at higher chamber pressures. No indication of explosion in the coolant channels or manifolds at engine shutdown was observed.