GB2143894A - Internal combustion engine ignition control - Google Patents

Abstract

The igniting element X is positioned near one end of a primary duct A open to the combustion chamber at the other end and of low impedance to gas flow over the whole engine speed range. This duct is continued as a secondary duct or ducts B of broadly equal cross section area to communicate with the combustion chamber. The ducts B have low impedance to gas flow at low and starting engine speeds but with an impedance to gas flow which is high compared to the impedance of the primary duct at higher engine speeds. Residual non-ignitable gas held in the ducts A and B is compressed by inflow of combustible mixture both via the primary and secondary duct sections during the compression stroke. At higher engine speeds the combustible mixture reaches the element X earlier in the compression stroke to provide more advanced ignition. The element X may be a spark plug, catalytic surface or an electrically or combustion heated glow plug. <IMAGE>

Description

SPECIFICATION Internal combustion engine with improved ignition system Control of power in spark ignition internal combustion engines, of the kinds used at the present time in road vehicles, is by control of the total charge of fuel-air mixture admitted in each working cycle.

These engines have a maximum power which is about three times the average requirement.

The induced throttled charge is initially much below atmospheric pressure under average running conditions.

It is known that a higher thermal efficiency is obtained in an i.c. engine if the fuel per cycle is controlled and the air per cycle is kept at the highest practicable value.

But the spark ignition used at the present time in the engines of many road vehicles is not capable of propagating combustion throughout a hydrocarbon fuel and air mixture where the fuel fraction is less than about 80% of the chemical combining proportions. (Ref.

H. Ricardo; The High Speed Internal Combustion Engine) In the engine of the invention now described ignition is by a solid igniter surface with which the compressed fuel and air mixture makes contact. The igniter surface is heated to a temperature in the region 500"C to 1 200 C, or it is otherwise catalytic to the combustion.

It appears in trials that the arrangement according to the invention gives flame propagation in fuel-air mixtures where the fuel fraction is much less than 80% of the combining proportion.

It is usually necessary to vary the ignition timing, for example as between starting and running, and in a form of the presently described invention, the arrival phase of the ignitable gas at the igniter surface is varied with engine speed.

The ignition surface in engines according to the invention now described, (and this ignition surface may in some embodiments of the invention be the heated surface of a glow plug) is held in a duct of small bore of which both ends open into the combustion chamber of an engine cyliner.

A representation of this ignition duct is shown in Figs. 1 and 2 with its axis shown as a straight line, and with open ends at A and B.

The ignition surface is shown at X in Figs. 1 and 2. From A to X the wall of the duct is smooth to allow easy gas flow, but in the end section near the end B, the duct, while of the same order of flow section as in the X to A section, has an impedance to gas flow formed at Z. This impedance is arranged to dissipate gas momentum.

In Fig. 1 let it be supposed that the ignition duct was initially filled with non-combustible gas as at starting, and that it is now surrounded with combustible gas in the combustion chamber of a reciprocating engine where the piston has risen slowly to the top dead centre.

During the slow compression, as at starting, combustible gas has entered at A and B at nearly equal rates.

The non-combustible gas is now compressed to the short column a, to b,. The ignition surface is at X and so the column of gas from X to A carries a flame to the combustion chamber in the form of a jet.

In Fig. 2 the compression rate has been much faster and the impedance Z has caused the compressed non-combustible gas to take a position such as a2 to b2.

At the higher speed the inflammable gas entering at A has made contact with the ignition surface earlier than at the starting speed.

The best dimensions are not yet known.

The movement of gas in the ignition duct at practical compression rates is taken to be. in phase with the piston. The gas column in the small bore duct has no larger diameter eddy motion.

In Fig. 3 the ignition duct is shown in what approximates to an experimental form. The bore from X to A has been varied from 3 mm to larger diameters; the length X to A was approximately 16 mm.

The igniter solid surface has an effective area which may be that of a small glow plug, that is about 0.5 sq.mm, or in a larger engine it may be of the order of 1.0 sq. cm.

The temperature of the ignition surface requires to be generally in excess of 500 C The required heating of the igniter may be obtained by electrical current in the material of the solid which provides the ignition surface.

This surface in another embodiment of the invention may be heated from another source.

Radiation may be used to transfer energy from such a source. The fuel-air combustion may be a source. The igniter surface in another embodiment of the invention may be catalytic to the fuel-air combustion.

In one embodiment of the invention the heating current in a solid igniter element is provided by a high frequency transformer, preferably operating in the hundred kilohertz range, mounted on a plug formed igniter generally as shown in Fig. 3.

In an embodiment of the invention spark ignition may also be provided. The spark gap may be in the neighbourhood of X or elsewhere. Spark ignition may in some engines according to the invention be used at starting.

The discs shown in Fig. 3 as part of Z may have the B holes on different axes. These elements of Z, discs in Fig. 3 of fins in Fig. 1 and Fig. 2, require sufficient heat transfer to keep them below ignition temperature.

Dimensions are mainly determined by the compression ratio. More than a single igniter may be used at more than one station.

Claims (5)

1. An ignition system for recriprocating internal combustion engines of the type which compress a fuel/air mixture in the combustion chamber said ignition system comprising an igniting element sited in a narrow bore duct of which a primary length from said igniting element to the combustion chamber is of low impedance to gas flow an inner secondary length from the igniting element to the outer secondary length said inner secondary length formed to accommodate and locate said igniting element together with that gas body which filled at the start of compression the whole ducts of the ignition system described herein said resident gas body compressed to the condition at firing time said inner secondary length joining an outer secondary length said outer secondary length comprising one or more channels inner-connected or not said channels communicating with combustion chamber by a route other than wholly by the primary duct said channels of a total mean cross section area of the same order as that of the primary duct said outer secondary length being of low impedance to gas flow at low rates of compression as at engine starting but of higher impedance to gas flow than the impedance of the primary length at rates of compression corresponding to the engine running the nominal junction between inner and outer secondary ducts being the diffuse boundary between said gas body compressed to the condition at firing time and fuel/air gas mixture from the combustion chamber another such boundary existing at this time in the neighbourhood of the igniting element.

2. An ignition system as claimed in Claim 1 wherein the igniting element is an electrically heated solid surface.

3. An ignition system as claimed in Claim 1 wherein the igniting element is a catalytic surface.

4. An ignition system as claimed in Claim 1 wherein an igniting surface is heated by the engine combustion.

5. An ignition system according to any preceding claim co-operating as an item in an engine using variation of fuel/air ratio exclusively or otherwise to control engine power.