GB2097057A

GB2097057A - Ejector reduction of I.C. engine exhaust back pressure

Info

Publication number: GB2097057A
Application number: GB8204163A
Authority: GB
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1981-02-13
Filing date: 1982-02-12
Publication date: 1982-10-27
Also published as: DE3204952A1; FR2500058A1

Abstract

A compressor 12 driven by the engine 1 is provided to supply compressed air to the nozzle 8 of the ejector 6. The engine exhaust pipe 5 is connected to an exhaust pressure reducing chamber 17 of the ejector, whereby the back pressure in the exhaust pipe may be reduced, the gases being discharged through a pipe ejector 6. The engine exhaust pipe 5 is connected to an exhaust pressure reducing chamber 17 of the ejector, whereby the back pressure in the @

Description

SPECIFICATION Exhaust system for an internal combustion engine The present invention relates to an exhaust system suitable for a four-stroke internal combustion engine.

The or each piston of a four-stroke internal combustion engine discharges burnt gases from its cylinder against the back pressure during the exhaust stroke and this requires a certain amount of work. On the other hand, during the induction stroke, the or each piston draws an air-fuel mixture into its cylinder through an opening controlled by a throttle valve. The difference between the back pressure and the intake pressure is called the pumping loss. In operation where the throttle is wide-open, the intake pressure in the induction passage is relatively high and the back pressure is nearly equal to the atmospheric pressure. Therefore, the pumping loss for wide-open throttle operation is small.

However, during operation with a part-open throttle, the intake pressure in the induction passage is lower than that in the case of wideopen throttle operation. Generally, therefore, the pumping lbss increases with part-open throttle operation and this causes a decrease of the thermal efficiency resulting in a deterioration of fuel consumption.

An object of the present invention is to provide an exhaust system which is capable of decreasing the back pressure, whereby the pumping loss may be reduced.

According to the present invention, an exhaust system suitable for a four-stroke internal combustion engine comprises an ejector consisting of an exhaust pressure reducing chamber, a nozzle in the chamber, and a suction throat pipe adjacent to said nozzle; a compressor arranged to be driven by said engine; a pipe for connecting said compressor with said nozzle of the ejector; a pipe connecting the exhaust port(s) of the engine with said exhaust pressure reducing chamber; and an exhaust pipe connected to said suction throat pipe.

In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure la is an indicator diagram of a conventional four-stroke internal combustion engine; Figure 1 b is an indicator diagram of a fourstroke internal combustion engine according to the present invention; Figure 2 is a sectional view of one embodiment of the present invention; and Figure 3 is a sectional view showing another embodiment of the invention.

Referring to Figure 1 a, the back pressure is P, and the intake pressure is P2. The pumping loss Lp is represented by the area A-B-G and the work L is represented by the area C-D-E-F. In the indicator diagram of Figure 16 according to the present invention, the symbols L' and Lp' correspond to those of L and Lp above-mentioned.

Conditions for producing the same power by the engine of the present invention as the conventional engine may be written as follows: L Lp=LLpLC ( 1 ) where: L' is the work, Lp' is the pumping loss, and Lc is the compressor driving loss.

If the friction loss plus mechanical losses Lf of both engines are equal, the equation becomes: L-L,-Lf=L'-L,'--LcL, (2) which may be written in the form: L-- Lp Lf L LD Lf L' L L' L This equation may be written into the form of efficiency equation: L' (3) L In order to obtain 171 > 77, the condition of L' - > 1 L is necessary.Accordingly, from the equation (1), necessary condition is: Lp > Lp'=Lc (4) Since the pumping loss Lp is proportional to (P 1-P2) and the compressor driving loss Lc is proportional to the pressure of the ejector Pc/ the equation (4) may be rewritten in the form: /3(P, P2) > ,B(P1 P2 )+YPC (5) where p is a constant dependent on engine specifications, y is a constant dependent of ejector specifications and air flow velocity.

The back pressure P,' is determined by the efficiency of the ejector. Thus, the back pressure P11 is a function of y Pc and ejector specification (E), which is written in the form: P1,=F(y PC,E) (6) Thus, the most preferable efficiency TI' may be obtained by selecting the specification for satisfying the equation (5).

Referring the Figure 2, which shows a first embodiment of the present invention, an engine 1 is provided with an air cleaner 2 in communication with a carburettor 3 and the latter is in communication with an intake port of the engine. An exhaust pipe 5, connected at one end to an exhaust port 4, is also connected to an ejector 6. The ejector 6 comprises an exhaust pressure reducing chamber 7, a nozzle 8 extending into the exhaust pressure reducing chamber and a suction throat pipe 9, one end of which extends into the exhaust pressure reducing chamber 7 facing the nozzle and the other end of the pipe 9 is connected to an exhaust pipe 1 0.

The nozzle 8 is connected to a compressor 12 by way of an air pipe 1 The compressor 12 is adapted to be driven by the engine from the crankshaft by means of gears or chains or the like.

A part of the exhaust pipe 5 constitutes a heat exchanger 1 5 which is positioned adjacent to and situated upstream of the ejector 6. The heat exchanger 1 5 comprises an outer tube 14 connected to the exhaust pipe 5 and to the chamber 7 and an inner tube 13 which is connected to the air pipe 11.

Compressed air from the compressor 1 2 jets from the nozzle 8 at a high speed to create suction in the suction throat portion between the nozzle 8 and the pipe 9. Thus, the back pressure in the exhaust pipe 5 is reduced.

The compressed air is heated by the heat exchanger 1 5. Velocity W of the jet air can be expressed as:

where: Wo is velocity before the nozzle, y is expansion ratio (Po/P, where Po: pressure before the nozzle; P: pressure after expansion), T is absolute temperature of air before the nozzle, R is gas constant, k is ratio of specific heat, 71n is nozzle efficiency, and g is gravitational acceleration.

From the equation, it will be appreciated that jet air of a higher velocity can be generated by elevating the air temperature T. Thus, a decrease of the back pressure is promoted by heating the compressed air with the heat exchanger 15.

Referring to Figure 3 showing a second embodiment, the same parts as the system of Figure 2 are identified by the same reference numerals. The system is similar to the system of Figure 2 in construction except that the heat exchanger is omitted. Although the system of this embodiment is not provided with a heat exchanger, the back pressure may be reduced by the operation of the ejector 6.

From the foregoing, it will be understood that the present invention provides a system which reduces the back pressure by an ejector provided on the exhaust pipe whereby the pumping loss may be reduced.

While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that this disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended

Claims

claims. Claims

1. An exhaust system suitable for a four-stroke internal combustion engine comprising an ejector consisting of an exhaust pressure reducing chamber, a nozzle in the chamber, and a suction throat pipe adjacent to said nozzle, a compressor arranged to be driven by said engine; a pipe for connecting said compressor with said nozzle of the ejector; a pipe connecting the exhaust part(s) of the engine with said exhaust pressure reducing chamber; and an exhaust pipe connected to said suction throat pipe.

2. The exhaust system of an internal combustion engine according to claim 1 , further comprising a heat exchanger by which exhaust gases are used to heat the compressed air passing from said compressor to the nozzle.

3. The exhaust system as claimed in claim 2, in which the heat exchanger comprises a chamber defined by part of the pipe connecting the exhaust port(s) with the pressure reducing chamber with part of the pipe connecting the compressor with the nozzle extending through the chamber.

4. An exhaust system for a four-stroke internal combustion engine substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.