GB572192A - Improvements in and relating to multi-cylinder 2-stroke cycle internal combustion engines - Google Patents

Abstract

572,192. Two-stroke engines. ARMSTRONG WHITWORTH & CO. (ENGINEERS), Ltd., SIR W. G., MANSFIELD, W. P., and WHITE, J. Feb. 1. 1944, No. 1866. [Class 7 (ii)] A multi-cylinder two-stroke internal-combustion engine has the exhaust openings of each cylinder connected by separate supercharging ducts to the inlet openings of another cylinder, the number of cylinders, crank spacings, and timing being arranged so that the exhaust opening of each cylinder occurs near the end of the charging period of its connected cylinder, the charge per cylinder being sufficient to charge the cylinder to the required high pressure and pass an excess charge to the supercharging duct.. The said excess charge is compressed by the exhaust action from the connected cylinder and delivered back to the cylinder as a supercharge. In a four-cylinder engine (Figs. 1 and 2), the inlet ports d are connected through non-return valves e to the air manifold f. The exhaust openings of each cylinder are connected to the inlet openings of another cylinder by the ducts g<1> to g<4> arranged as shown in Fig. 1, each duct having an outlet h leading to the atmosphere, silencer, turbine or other auxiliary apparatus. Thus, when an exhaust event occurs in No. 1 cylinder, some of the exhaust energy passes along duct g<1> and forces the excess charge which has passed through No. 4 cylinder back into the cylinder as a supercharge. The maximum effect of this exhaust action occurs just as the inlet openings close. A three-cylinder engine will give 120 degrees between exhaust events, the same spacings being attained with 6, 9 or 12 cylinder engines by connecting every second, third or fourth cylinder respectively in the firing order. A timing diagram for a four-cylinder engine is shown in Fig. 9. The inlet belt c is of minimum volume necessary to provide the charge movement. The non-return valves e prevent reverse movement of the charge out of the cylinder. In some cases, each cylinder may be provided with two sets of inlet orifices, Fig. 5, consisting of main charging orifices q and supercharging orifices r leading to the supercharging duct. In this form, the main orifices are closed before supercharging occurs. Preferably, the supercharging ducts should all be of the same length as shown in Fig. 1. By tapering the supercharging duct between the inlet orifices, the exhaust action is confined to give increased pressure. The loss of energy through the openings h during the supercharging period may be avoided by providing a cyclicallyoperated valve driven from the engine and controlling the outlet from each supercharging duct. This valve closes before each exhaust event and opens when the supercharging of the connected cylinder has been completed. A three-cylinder engine of this form is shown in Fig. 4, the outlets s from the supercharging ducts being controlled by disc valves n provided with slots t which open the outlets at the required times. The exhaust duct i beyond the openings s may be constructed so that the pressure wave following exhaust is followed by a zone of low pressure in the supercharging duct and cylinder, thus facilitating scavenging and charging. The valves n are enclosed by a cover u and may be cooled by water, air, oil, &c. In some cases the outlets from several supercharging ducts may be controlled by the same disc valves. For operating the engine without supercharging the gases may be byepassed so that they do not pass through the rotating disc valve. The exhaust gas in the pipe i may be used to drive a turbine a operating a charging-blower b. The length of the duct i should be such that positive reflections from the turbine inlet reach the supercharging duct at the time when the next exhaust event occurs. The required length is based on a mean wave velocity of the order of 400-550 metres per second depending mainly on engine speed and degree of supercharge. The valve n is closed when the reflected exhaust wave reaches it, thus trapping the gases and forming a highpressure zone favourable for driving the turbine and preventing interference with low-pressure scavenging and charging. In a modification, Fig. 7, each supercharging duct has two outlets k, l, the first leading to the duct i and the second to a duct m leading to atmosphere or silencer. The valves have openings v, w for giving the required open periods. An additional valve p may be provided in the duct i to control flow to the turbine. When more than one exhaust duct is used, these may be connected separately to the turbine or to different sections of the turbine ring. The turbine may return power to the crank-shalt or drive another machine.