FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1920
1920 - 1312.PDF
to no less than 37 per cent, at about one-third full loadcorresponding to a fuel consumption of just under 0.36 pint of benzole per indicated horse-power hour. It will beseen that the curve of efficiency actually obtained follows the theoretical curve with a reasonable degree of approximation.In .Figs. 11-13 are shown some typical indicator diagrams taken from one of the two engines, with a Hopkinson opticalindicator. R should be noted that when working on this DECEMBER 30, 1920 In the writer's opinion the potentialities of working witha stratified charge cannot be over-estimated. It opens up the possibility of obtaining far higher efficiencies than are obtain-able by any other known means, and, what is perhaps equally important, it reduces the temperature of the cycle and withit all the troubles due to high temperatures which directly or indirectly are the root cause of most mechanical failuresSince the rate of heat flow to the cylinder walls varies roughly A f* sri: a. i» u 5 Oru MIXTURE. STRENGTH WEAK C«*m^n CMwumM »?ICM. to*/. »*A ttf «ft o uZ tot vAL «*% I \ ' F /* ^-—• o fa. a -^ 1 > I • 1- ClWVES SHOWING I M.E.P ^THERMKU EFFICIENCY *nr» VAI?VIN(; MIXTURE STUENSTH COMPRESSION RATIO 5 ' 1 Futu. BENZOL - j 1 i (J 111 h or •i MIXTURE STRENGTH FI us PER tu: INCH 3 S » 15 20 25 50 15 40 45 -F - 1 1—h~ ,1 •//z a . \ / Cui? si lf» STANDF i^#*O S.RO EF | •p-ic -~i i *>CTU^L t, THEOPE.T1CM. - DOWN TO THE POINT or NO HEAT SUPPUY. COMPRESSION R»VTIO. 5 : i 1 CCMfi M1X1 ru»t. system distribution troubles disappear. In any ordinarymulti-cylinder engine it is necessary so to proportion the mixture that the weakest cylinder receives a charge of acertain minimum strength to ensure regular running ; this means that other cylinders are receiving a slightly richercharge than is absolutely necessary and their efficiency is therefore reduced. On the other hand, when working witha stratified charge, the power output of each cylinder is dependent solely upon the quantity of fuel admitted to it,so that any cylinder which receives a richer mixture than others will develop correspondingly more power, and theeconomy will always be at a maximum, that is assuming, of course, that the mixture strength is at all times below thatrequired to consume the whole of the oxygen. Again, from the point of view of altitude compensation nothing could besimpler, for (so long as the oxygen in the cylinder is not all consumed) constant power can be maintained over anyreasonable range of density by merely supplying a constant fuel feed, e.g., by gravity, or if a carburettor is used in itscrudest form, the variation in power with altitude will correspond with the natural characteristic of the carburettor,and will therefore vary as the square root of the density. With a view to gaining further practical experience withthis system, one of the two gas engines-supplying power to the writer's laboratory was, about nine months ago, convertedto run with stratified charge and control on the fuel alone. Since that date it has run continuously under violentlyfluctuating loads and has developed no trouble of any kind. It is running in parallel with another engine identical inevery respect but working on the ordinary cycle. In the case of the latter engine it is necessary to remove the cylinderhead every two months for decarbonising and grinding in the exhaust valve, while the cylinder of the engine working onthe stratified charge has only been opened once, when it was found to be practically clean, while the exhaust valveappeared to keep almost as cool as the inlet valve in the other engine. As regards governing and regularity of running as the cube of the temperature, and the power output prac- tically directly as the temperature, it follows that quite a small reduction in power will reduce the heat losses to an extent that must render air-cooling quite a simple problem. The pessibilities of working with a short compression and long expansion stroke deserve careful consideration. In effect this can be accomplished by the simple expedient of O 5 IO ?* S !« ii J 30 4-u —1-/75. •J-V 1 . MIXTURE STRENGTH runoow •; 15 » !S SO SB 4O «S • j 1 AW CYCLE Emc H i LJI c •—= EHCY - —• 1 i . CUKVE& 5HOWINS EFFlCltMCIfcfe & Ml? B I .ULt TURC i E.NO STRENGTH ME FOR 1 closing the inlet valve late, so that compression does not startuntil well up the compression stroke ; this method has both direct and indirect advantages. The direct advantages arethat while the compression pressure is controlled by the nature of the fuel, the expansion ratio can be extended toany degree and very high efficiencies can be obtained, though, Fie. 17. there is nothing to choose between the two engines, each ofwhich can develop a maximum of 24 b.h.p. at 750 r.p.m. Although the above experiments suggest that the systemhas been developed to a practical stage, the writer feels that this is hardly yet the case, and that considerably moreresearch is required before it can be considered wholly satisfactory. of course, at the expense of the power developed per unit ofcylinder volume. For example, suppose that a fuel of toluene value O isused, then while the compression ratio is limited to 4.85 : r on the ground, the expansion ratio may be say 8:1. Thelimiting efficiency for 4.85 : 1 expansion is 32.7 per cent., and for 8 : 1, 40.6 per cent. The power output under these 1314
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
