Practical Conclusions
Airplanes require about one third more power during the take-off than in flight. In diesel-engined airplanes the size of the engine could be reduced by 25 percent by feeding oxygen into the intake air during the takeoff. Applying the results of the experiments to a transport plane, Fig. 31 shows the possible weight saving with various oxygen boosts. The curves are based on 6000 cruising horsepower and an estimated engine weight of 2 lb per hp.
For the take-off 8000 hp are necessary. To supply the additional 2000 hp, 200 lb of oxygen are fed into the intake air during the take-off. The volume of 200 lb of liquid oxygen is approximately 20 gal. Standard liquid air containers of 55 litre capacity weigh 75 lb. Therefore the weight of the oxygen and container is 350 lb while the possible saving in engine weight is 4000 lb. The weight per take-off horsepower is thereby reduced from 2 to 1.54 lb. The calculation is shown in Table 1.
| Figure 38.—Effect of Oxygen Boost on Power and Weight. (Cruising horsepower 6000, takeoff horsepower 8000.) |
Oxygen addition may be used for starting diesel engines. The raising of the oxygen concentration from the normal 21 per cent to 45 per cent was found to be equivalent to a raise of approximately 10 cetane numbers as far as starting is concerned.
Five per cent increase in oxygen concentration eliminated exhaust smoke completely.
Table 1
| Normal horsepower | 6000 |
| Take-off horsepower | 8000 |
| Normal fuel consumption | 0.4 lb per hp-hr, or 53.5 lb per min |
| Normal air consumption | 900 lb per min |
| Normal oxygen consumption, 21 per cent oxygen concentration | 189 lb per min |
| Boosted oxygen consumption, 32 per cent oxygen concentration | 289 lb per min |
| Oxygen to be supplied | 100 lb per min |
| Weight of 8000-hp engine | 16,000 lb |
| Weight of boosted 6000-hp engine | 12,000 lb |
| Weight of oxygen for 2-min boost | 200 lb |
| Weight of container for 29 lb of liquid oxygen | 150 lb |
| Net weight saving by oxygen boost | 3650 lb |
| Weight per horsepower, nonboosted engine | 2 lb |
| Weight per horsepower, boosted engine | 1.54 lb |
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