GB2225386A

GB2225386A - I.C. engine exhaust system

Info

Publication number: GB2225386A
Application number: GB8926784A
Authority: GB
Inventors: Patrick Graham Hansen
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-11-25
Filing date: 1989-11-27
Publication date: 1990-05-30
Also published as: GB8926784D0

Abstract

Each exhaust port 1 has a primary exhaust pipe 2 attached at its exit from a cylinder head face 3. The primary exhaust pipe is connected at a junction 8 with a secondary exhaust pipe 5 communicating at its downstream end with another primary exhaust pipe (2', Figs. 3 and 4). At the flange 4 the flow cross-section at the inlet to the pipes 2 and 5 is greater than the flow cross-section of the port 1 to avoid turbulence and the creation of back pressure. <IMAGE>

Description

EXHAUST ARRANGEMENT FOR AN INTERNAL COMBUSTION ENGINE The invention relates to trodifications to conventional arrangements of exhaust systems for fourstroke internal combustion engines, but not necessarily exclusively, as used in vehicles aimed at enhancing engine performance by making use of energy which exists in the exhaust gases.

It is well known that engine output may be increased by the use of a tuned length of pipe fitted to each cylinder of a multi-cylinder engine. These have been applied to both inlet and exhaust systems either singly or simultaneously. Dependent on the length chosen for the pipes it is possible to increase the engine output at and about one speed in particular, usually towards the top end of the engine speed range. Alternatively a morse modest increase of performance can be obtained by selecting or "tuning" the pipe length(s) over a much wider speed range.

It is an object of the invention to provide a modification to an orthodox, untuned, exhaust manifolding arrangement for multicylinder engines with a view to improving engine performance without the use of tuning pipes as normally understood.

According to the invention there is provided an exhaaust system for an internal combustion engine, comprising a primary exhaust pipe adapted to be connected to the outlet or exhaust port in a cylinder head and a secondary exhaust pipe connected between a primary exhaust pipe of a first cylinder and a primary exhaust pipe of a second cylinder, the internal lateral dimensions of the primary exhaust pipe being greater than that of the associated port.

The internal lateral dimension of the primary exhaust pipe downstream of the position where the secondary exhaust pipe from a second cylinder joins the primary exhaust pipe may be greater than the internal lateral dimension of the primary exhaust pipe at the junction.

Using the invention it is possible to provide that the flow of exhaust gases at both the upstream and downstream ends of a primary exhaust pipe at the junctions with the secondary exhaust pipe is directed primarily along the primary exhaust pipe in a sncoth or larellar flow. In this way turbulence is sought to be obviated which might set up unwanted back pressure in the secondary pipe and in any event could provide interruptions in the flow in both pipes.

In the arrangement embodying the invention, gas exiting the first cylinder has an influence on the gases at the exhaust port of the second cylinder during the exhaust stroke of the second cylinder.

Exhaust systems embodying the invention are hereinafter described, by way of exarrple, with reference to the accompanying drawings.

Fig. 1 is a part section through an exhaust port of one cylinder of a multi-cylinder engine; Fig. 2 shows a fragmentary sectional side elevation of one form of a junction of primary and secondary pipes; Figs. 3 and 4 show a fragmentary sectional side elevation of a further form of a junction of primary and secondary pipes respectively during "sucking" and "blowing"; Figs. 5 and 6 show in tubular form performance data at positions 1-11 in Figs. 3 and 4; and Fig. 7 shows graphically the results of Figs. 5 and 6, as a plot of vacuum in inches against gas flow in cubic feet per minute (CFM).

Referring firstly to Fig. 1 of the drawings, there is shown a section through a typical exhaust track in a cylinder head of a multi-cylinder engine to which the invention is applied. Such a cylinder head, which also contains one or more inlet gas ports and valves, not shown, encloses the top of the engine cylinder block in the cylinders of which pistons operate to carry out the working events of a four-stroke engine and convert the gas work during the expansion stroke part of the cycle into output torque and power via connecting rods and the crankshaft. The e exhaust valve(s) is or are operated by means of a crankshaft, as is the inlet valve(s) not shown, to open and close at predetermined regular timings in relationship to the crankshaft and piston movement during each working cycle.

The timing intervals between sequential cylinders are determined by the number of cylinders, the crankshaft arrangement and the firing orders chosen for a particular engine.

Each exhaust track, or port 1, has a primary exhaust pipe 2 attached at its exit from the cylinder head face 3 usually by a bolted flange 4.

The primary exhaust pipe is connected with a secondary exhaust pipe 5 adjacent to port 1. The secondary exhaust pipe 5 is connected at the downstream end with a primary exhaust pipe 2' of the previous cylinder in the firing sequence of the engine. In a four cylinder engine firing order can be 1 - 2 - 4 - 3 - 1 with the pipes 2, 5 being connected in pairs.

Welds 6, 7 show where pipe sections are connected.

At the port 1, the internal diameter of the primary exhaust pipe 2 at its junction with the secondary exhaust pipe 5, and internal diameter of that pipe 5 are greater than the diameter of the port 1. Stated in another way the exhaust port is smaller that the mouth of the pipes. Therefore exhaust gases exiting the port 1 discharge, in the direction of flow as shown by the arrows, directly into the pipe 2, in a smooth flow as it does not engage any pipe lips 8' at the junction 8. This results in the avoidance of turbulence at the junction and in the pipe which would effect the gas flow for exarrple by setting up back pressures particularly in the secondary exhaust pipe 5 which would have a deleterious effect on engine performance.

In a similar manner, the downstream end 9 of the primary exhaust pipe 2' at the junction 10 with the secondary exhaust pipe 5 from a second cylinder is greater in diameter than the upstream end 11 so that gas flow across the junction is smooth and lamellar, in other words the gas from 11 passes to a larger diameter pipe at 9.

Results from European cycle tests show reductions in the emission levels of carbon monoxide (CO) and nitrogen oxides (NOx) together with a 20% improvement in fuel consumption when the exhaust system according to the invention is fitted. Similarly the steady state tests show improvements in the carbon monoxide levels and significant improvements in fuel consumption.

Referring now to Figs. 3-7 of the drawings, Figs. 3 and 4 show a primary exhaust pipe 2' connected with a secondary exhaust pipe 5'.

In a four cylinder engine firing order can be 1 - 2 - 4 - 3 - 1 with the pipes 2', 5' being connected in pairs.

The downstream end of the primary exhaust at the junction 10' with the secondary exhaust pipe 5' from a second cylinder is greater in diameter than the upstream end so that gas flow across the junction is smooth and lamellar, in other words the gas passes to a larger diameter pipe at the junction 10'.

In a system modified according to the invention, there are achieved improvements in power, economy and exhaust gas emisions over conventional arrangements. Such a system is capable of modification to suit different engines and operating conditions wherein pulses and relative pressure levels in the various branches of the exhaust system provide improved exhaust conditions and better scavenging of the engine cylinders. These improvements, result from a high pressure release of gas when the exhaust valve opens. An object of the invention is thus to utilise this pulse in a direct manner to create a negative pressure that can assist the scavenging of the following cylinder in the firing order.

Th achieve this objective the pulse (travelling at a speed in the region of 600 metres per second), will take the most direct route available to it. Hence it will travel directly out of the port and down the pipe directly off the port. Further downstream in this pipe, the pulse will travel through the junction constructed and will create a negative pressure in the larger pipe at this junction. This negative presure is then made available by interconnection, to assist the evacuation of the balance of exhaust gas from the following cylinder in the firing order.

Once again, the high pressure pulse from this cylinder will travel via the most direct route, and because of the very high velocity will by-pass the negative pressure available at the exhaust port and once again take the most direct route and proceed to do its work in the following junction. The balance of exhaust residue will then be dispersed into the negative pressure provided by the previous cylinder, thereby providing more complete scavenging and reducing the work load required from the engine to evacuate this cylinder. It also provides more complete evacuation and a reduction in contamination of the incoming charge.

Claims

1. An exhaust system for an internal combustion engine, cart- prising a primary exhaust pipe adapted to be connected to the outlet or exhaust port in a cylinder head and a secondary exhaust pipe connected between a primary exhaust pipe of a first cylinder and a primary exhaust pipe of a second cylinder, the internal lateral dimensions of the primary exhaust pipe being greater than that of the associated port.

2. An exhaust system according to Claim 1, the internal lateral dimension of the primary exhaust pipe downstream of the position where the secondary exhaust pipe from a second cylinder joins the primary exhaust pipe being greater that the internal lateral dimension of the primary exhaust pipe at the junction.

3. An exhaust system according to Claim 1 or Claim 2, the primary and secondary exhaust pipes being connected at a junction adjacent the port, the internal lateral dimension of the port being less than that of the junction.

4. An exhaust system for an internal combustion engine, substantially as hereinbefore described with reference to the accopanying drawings.

5. An internal combustion engine, including an exhaust system according to any preceding Claim.

6. A method of operating an internal combustion engine according to Claim 5, wherein exhaust gases are arranged to flow smoothly from an outlet or exhaust port thereof into a primary exhaust pipe.