References are made to published results of similar tests of air-cleaner devices conducted in 1922, and the scope of the 1924 tests is described. Road tests of air-cleaners were carried out and the tabulated data are presented. Efforts were made to find out how much dust the engine would draw in if the cleaner and connections were removed and to catch and weigh the dust the air-cleaner under test failed to catch.
Dust was raised by a car running about 50 ft. ahead of the test-car and, to produce heavy dust-conditions, the road was dragged with a chain attached to the car and forming a loop behind it. The leading drivers maintained as nearly as possible a constant speed of 25 m.p.h. and chose the dustiest part of the road, following the same course on all the rounds.
The specific items of the 1924 program were (a) to continue the testing work begun in 1922, (b) to devise a satisfactory method of testing types of air-cleaner that cannot well be tested by the 1922 method, (c) to determine how much dust an automobile or truck encounters in service and (d) to find out how the use of air-cleaners affects the rate of engine wear.
After describing the “absolute” air-cleaner used in connection with the air-cleaners under test, standard dust for testing purposes and Fuller's earth are discussed, as are also some tests made of the latter substance. Road-tests are treated generally and specifically, road-test and laboratory-test comparisons are made, and the 32 air-cleaners submitted for test are described, together with tabular data of the results obtained while testing them.
Air-cleaners have different degrees of efficiency. Certain places exist in the United States and elsewhere where it is worth having an air-cleaner of any sort on an automotive machine, if the cleaner has any efficiency whatsoever. On a typical desert road in California, the dust and sand encountered constitute a very different proposition from that found on the highways. In New Mexico, Southern California, Texas and Arizona, I have known of cases in which sandstorms have cut the enamel entirely off one side of a car, clear down to the bright steel. In such cases it is not necessary that the air-cleaner should be efficient to do a great amount of good. About 5 years ago I saw an air-cleaner on a tractor in Northern California that was nothing more than a periscope. Its efficiency as an air-cleaner was about 97 per cent. The engineer of a large fig-growing holding near Fresno, Cal., told me that tests he had made showed a periscope 2 ft. high to be capable of taking out 90 per cent of the dust that was encountered by the engine.
I am not predicting at all that automobiles will be equipped with periscopes that will extend into the air above them, but perhaps such a use on trucks is possible. A periscope might be developed that would go up on the inside of the cage or front part of the machine and yet not be unsightly; but, for automobiles, I think that would be practically out of the question. However, I want to make a plea for the ordinary user of automobiles. Not 1 per cent of the cars in use give evidence that the designer has devoted any thought whatever to the possibility that an air-cleaner might be wanted on the engines of the car. The same statement is true for trucks. It costs about $5 just to make it possible to put an air-cleaner on some machines.
The laboratory tests here reported follow closely those of the 1922 series. The 1922 results are stated briefly in the University of California Agricultural Experiment Station Bulletin No. 362, entitled Dust and the Tractor Engine. Also, they are given in detail in Agricultural Engineering, June and July, 1923.
The road-tests were made because the regular laboratory test was inapplicable to some cleaners that were sent in for test. Considerable study was given the subject so that the road-tests as run might be duplicated readily elsewhere. Two main things are sought: First, to find out how much dust the engine will draw in if cleaner and stove and their connections are removed; second, to catch and to weigh what the tested cleaner fails to catch. To determine the dust encountered, a 90-deg. ell of plumbers' thin brass tubing having an outside diameter of 2 in. is placed with its opening forward on the level with the midline of the radiator core and, longitudinally and laterally, as near as possible to the regular position of the carbureter inlet on the car or the truck on which the test is made. The hood is closed, holes being cut for connections to the “absolute” cleaner. The absolute cleaner is a slight modification of No. 17 of the 1922-test series. The run with the cleaner off is made as nearly as possible like the run with the cleaner on.
Dust is raised by a leading car 50 ft. ahead. For heavy dust-conditions, a standard chain is dragged in a loop. For medium dust, no drag is used. The dust per mile caught in the absolute air-cleaner is made the basis of the efficiency determinations. Check-runs are necessary. The leading driver endeavors to maintain a constant speed of 25 m.p.h., to pick the dustiest part of the road and to follow the same course as nearly as possible on all the rounds. The data are interpreted in accordance with what is deemed to give results nearest to the truth, when the circumstances of the tests are known, and reference is made to the notes in connection with the road-test tables.
Too much stress should not be placed on the results of these first road-tests. They should first be verified by several repetitions. The position of the air-cleaner on the car, the tightness of the fan-belt, the diameter and the design of the fan, the car speed, type of soil, conditions of road, wind, weather and the like may change the results very appreciably. In the road-test of June 2, the fan-belt was found slipping considerably at the close of the tests. Also, on that day, Cleaner No. 56 was found shifted slightly from its correct position.