The strict requirements of similarity theory are shown to be so numerous and restrictive that complete modeling of combustion processes is practically impossible; all successful modeling so far has involved deliberately ignoring many of the similarity rules. The paper reviews some of the more notable examples of this partial modeling, and mentions the physical facts which underlie their success. It is emphasized that every combustion-modeling technique represents a compromise between the requirements of cheapness and reliability.

The newly devised techniques for studying the effects of turbulence on homogeneous gas flames in two-dimensional open burners through the determination of (1) the mean flow field in the neighborhood of the flame front, (2) the position of the mean flame front and the root-mean-square displacement of the mean flame front, (3) the local turbulent flame velocity, and (4) the position of the instantaneous flame front have been refined and extended to several conditions of flow, turbulence, air-fuel ratio, and burner size. This technique has also been extended to study the growth of wrinkles in the instantaneous flame front by high-speed photography. The experimental results obtained indicate the following: (1) For all of the conditions investigated the effect of turbulence on the flame is only to wrinkle and extend the surface of the flame front. (2) The ratio of the local turbulent flame velocity to the laminar flame velocity, ST/SL, can be correlated, as indicated in the previously presented theory of Scurlock and Grover, with the dimensionless time parameter, SLt/l2 (where t is the time of exposure of the flame element to the turbulence and l2 is the Eulerian scale of turbulence), and the dimensionless turbulence intensity in the approach flow v0′/SL (where v0′ is the turbulence intensity). (3) ST/SL can be correlated with the root-mean-square displacement of the mean flame front, (γ2¯)12. These results also verify that a useful technique has been developed for studying the effects of turbulence on flames.

T h e feasibil i ty of r o t a t i n g a bluff flameholder as a m e a n s of inc reas ing vo lume t r i c hea t r e l ea se r a t e s i n h i g h o u t p u t c o m b u s t i o n c h a m b e r s h a s b e e n inves t iga ted . A cy l indr i cal flameholder w i t h i t s l o n g i t u d i n a l axis n o r m a l t o t h e flow of c o m b u s t i b l e gases was r o t a t e d rap id ly a b o u t a t r ansverse axis para l le l t o t h e flow. T h i s r o t a t i o n r e su l t ed in t h e gene ra t i on of flame f ron t a t h i g h e r r a t e s t h a n w h e n t h e flameholder r e m a i n e d s t a t i o n a r y , a n d v o l u m e t r i c h e a t release r a t e s were cor respondingly increased . R o t a t i o n of t h e flameholder, however , also t e n d s t o r educe t h e s tab i l i ty l i m i t s . For a n y o n e t a i lp ipe l e n g t h , t h e c o m b u s t i o n efficiency increased w i t h inc reas ing r a t e of r o t a t i o n . T h i s increase t e n d e d t o b e g rea te r t h e lower t h e i n l e t gas veloci ty . T h e power r equ i r ed t o overcome t h e r o t a t i o n a l d r a g was ca lcu la ted t o be usua l ly less t h a n t h e losses d u e t o wall fr ict ion or axial d rag of t h e flameholder. Possible appl ica t ions of r o t a t i n g flameholders a re discussed.