From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical article from 'Automotive Industries' magazine discussing improvements in engine intake manifold design and carburetor application.
| Identifier | ExFiles\Box 50\3\ Scan042 | |
| Date | 27th January 1921 | |
| January 27, 1921 AUTOMOTIVE INDUSTRIES THE AUTOMOBILE 165 does not strictly confine the heat to the ribbed portion for practical reasons. The effect of the intake pipe construction upon the remainder of the intake passages to the cylinders is very important. Off-hand it would appear as though the deep ribbing would offer a severe obstruction to the fuel passing to the cylinders. Let us compare what happens with that of the ordinary manifold where the fuel as a rule travels very much slower than the air-stream flowing along the manifold walls. A considerable time interval occurs between the time the fuel leaves the carbureter nozzle and the time it reaches the cylinder. In the case of the intake pipe, Fig. 6, and the remaining passages to the cylinder, a highly heated surface can be used without heating the air, the vapor becomes so highly heated that it does not condense while in the air-stream. Of course, the vapor going into the air-stream receives a high velocity on the outset, and the time interval for it to condense is small. Most convincing observations are made when applying 2-in. carbureters to the engine, both on the dynamometer and on the road. For speeds below 800 r.p.m. with open throttle, the plain unheated intake-pipe could not be used at all. Even at higher speeds the economy was poor although the power was good, indicating poor distribution. With the new design intake-pipe the engine could be run as low as 200 r.p.m. with wide-open throttle. However, this was not true with 2-in. plain-tube carbureters which we have tried without making structural modifications in the design. Application of the exhaust-heated intake manifold made it possible to equip the engine with a 2-in. carbureter. The car accelerates well in cold weather, without using a choker, by the time it can be driven out of a cold garage onto the street. A manually operated valve is provided to force all the exhaust heat through the intake. This is used until the engine heats to the normal operating temperature, or it can be left on continuously without causing any harm except a slight restricted exhaust passage for high speed in this particular experimental design. The good acceleration while cold indicates super-heating of the fuel; in other words, it does not condense materially before reaching the cylinders, even when the engine is cold. When using the larger carbureter and developing correspondingly higher power at both low and high speeds, there is a smoothness in operation that never was obtained with smaller carbureters. The degree of flexibility, smoothness, economy and power are far in advance of the best previous results. The engine shows good torque, right down to the point of stalling. It is believed that even these preliminary investigations show that the conventional hot-spot method can be far surpassed and that the fuel can be heated without unduly heating the air. Here again the results obtained are a direct result of the change in viewpoint. We will next consider tests showing the effect of a proper correlation of car and engine characteristics using 4.25 to 1 and 5 to 1 compression pistons in the same engine. First a brief description of the engine and testing apparatus will be given. The Engine Used in the Test The engine used in the test is a valve-in-head type with six-cylinders, 3⅜ x 5½-in. (295.2-cu. in. displacement). The cylinder block and upper crankcase is a one-piece casting of aluminum alloy, with inserted cylinder sleeves of cast iron machined all over. The cylinder-head is of cast iron and detachable. Fig. 7 shows a cross-section of the engine and gives a fairly good idea of the detailed construction. The crankshaft is of the three-bearing type and of liberal dimensions. The hollow crankpins are 2¼ in. in diameter and 1⅜ in. long. The shaft is drilled for oil passage at 25-lb. per sq. in. pressure to all the main and connecting-rod bearings. Attention is called to the unique cylinder-sleeve construction with particular reference to the application of the packing at the bottom of the sleeve. The sleeve at the bottom diameter has a snug slip fit in the aluminum case. The sleeve, however, has been shown to have a very slight axial movement here. This follows from the fact that the aluminum case is not subject to as great a temperature range as the cast-iron sleeve, the higher Fig. 7—Transverse section of engine used in the test Fig. 8—Inlet and exhaust cam layout. AB and BC are straight lines intersecting at sharp angle at B Text from Fig 8: .1572, .595, .278 LIFT, .610 R. {Sir Henry Royce} , .005, 50°, 90°, 10°, 25°, .707 R. {Sir Henry Royce} | ||