GB2502995A

GB2502995A - Dual Fuel Auto-ignition Engine

Info

Publication number: GB2502995A
Application number: GB1210431.1A
Authority: GB
Inventors: Marcos Alonso
Original assignee: Nissan Motor Manufacturing UK Ltd
Current assignee: Nissan Motor Manufacturing UK Ltd
Priority date: 2012-06-13
Filing date: 2012-06-13
Publication date: 2013-12-18
Also published as: GB201210431D0

Abstract

An Internal combustion engine cylinder uses a conventional primary fuel injector in an intake port 13, and an auxiliary fuel injector 17 for supplying an auxiliary fuel into the centre of a combustion chamber 15. The auxiliary fuel will auto-ignite when the mixture of primary fuel and air is compressed. The engine is preferably a four-stroke petrol (gasoline) engine that has no requirement for a spark plug to ignite the fuel-air mixture. The engine may comprise an integral or discrete cylinder head and a monospace combustion chamber. The auxiliary fuel may be diethyl ether. The engine produces reduced heat losses from a centrally produced flame front that propagates from the inside to the outside of the combustion chamber volume.

Description

Dual Fuel Auto-ignition Engine The present invention relates to an internal combustion engine, and particularly to a petrol (gasoline) engine where a fuel-air mixture is ignited to generate power, by compression ignition of an auxiliary fuel.

In a conventional petrol engine, combustion of the fuel-air mixture is initiated by a spark plug having electrodes which are necessarily close to a cylinder head wall. The general principles of operation for this type of spark ignition internal combustion engine have not significantly changed

since its first introduction.

while petrol engines are generally considered to be faster, guieter and lighter than, e.g. a diesel engine eguivalent, a spark plug ignition system is often a weak point in overall reliability.

Furthermore, due to the location of the sparking end of a spark plug close to the cylinder head wall in an engine, considerable heat losses occur on the cylinder head once the flame front of the ignited mixture is close to or reaches said cylinder head, leading to a decrease in the engine's thermal efficiency. It is preferable to initiate combustion of the fuel-air mixture as close to the centre of the combustion chamber as possible (or at least at a distance from the cylinder or piston walls) Therefore, a need has been identified to find an alternative to this method of ignition in a petrol engine. Prior art engines as described in 0N23,654,505Y, US5,050,550 and EP064,309 involve some overlap with features of the present invention, and the relevance of each will be discussed hereinafter.

In one broad aspect of the invention, there is provided an internal combustion engine including: at least one cylinder in a cylinder block; a piston mounted for reciprocating movement within the cylinder; a combustion chamber defined by the free volume in the cylinder when the piston is at the top of its stroke; an intake or injector port for supplying a fuel-air mixture to the combustion chamber; an exhaust port for removing exhaust gas from the combustion chamber; and an auxiliary fuel injector for supplying an auxiliary fuel into the combustion chamber that will auto-ignite when the fuel-air mixture is compressed.

In an example, the combustion chamber is bounded by the piston and by plural surfaces of the cylinder.

In an example, the engine comprises a cylinder head corresponding to the at least one cylinder, said cylinder head being fastened to said cylinder block and sealed thereto.

Where the engine comprises a cylinder head, the combustion chamber may be bounded by the piston, the cylinder walls, and the cylinder head.

In an example, the combustion chamber is a monospace. In this context, a monospace is a single, homogeneous cavity, without any side chambers or re-entrant features. This is advantageous in limiting the ratio of surfaoe area to volume, so as to minimize heat losses. There will be a groove around the piston head down to the top piston ring; this is a necessity for integrity of the piston ring, but is not a re-entrant feature, as the angle of entry into the groove is less than or equal to ninety degrees.

In the above definitions, the valves, fuel injectors, and any other necessary components in this area such as combustion chamber preheaters ("glow plugs"), are regarded as parts of the cylinder; or where fitted, the cylinder head.

The auxiliary fuel auto-ignites by virtue of the pressure and temperature of the compressed mixture in the combustion chamber to generate sufficient heat to trigger combustion of the primary fuel (i.e. the petrol-air mixture such as in an otherwise conventional petrol engine) Preferably the auxiliary fuel injector is arranged such that the auxiliary fuel is injeoted towards the centre of the combustion chamber. Hence, the flame front of the ignited auxiliary fuel will not start too close to the walls of the combustion chamber or piston, but will start at the centre of a relatively large volume (compared to the restricted area surrounding the electrodes of a spark plug), resulting in better engine performance from reduced heat loss and a quicker combustion process for the main fuel; as the explosion propagates outward from a central point in the chamber, rather than from a point close to one wall.

Tt should be noted that in the prior art, "dual fuel" type engines have been proposed. For example, ON 23,654,505Y describes an engine which runs in diesel mode at low engine revolutions; and which is able tc run with a mixture cf diesel and petrol at medium to high loads. However, the present invention is a petrol engine which uses a second (or "auxiliary") fuel as an ignition system for the petrol-air mixture.

US5, 050,550 describes a hybrid step combustion system, which may work as a normal diesel engine; or as a hybrid engine in which a mixture of petrol and air is ignited by diesel fuel injected during the compression stroke (supposedly at high loads) . It should be noted that this system uses a precoinbustion chamber for the diesel fuel, it is therefore an indirect injection diesel engine. Most modern diesel engines are direct injection engines, as these have been found to be more economical on fuel. Petrol engines do not need precombustion chambers. The present invention is essentially a pure petrol engine wherein there is an external (auxiliary) fuel source for starting the combustion, namely the self ignition of a small amount of diethyi ether injected into the combustion chamber fuel-air mix.

Regarding the above prior art, these systems are essentially diesel based engines which have been improved to work at higher loads through the combustion of a second, different, fuel which contributes to the work of the engine.

EP 0643209Al describes a diesel engine that reguires detection of a load on the engine. For example, when working at high loads, a main fuel is introduced into a combustion chamber prior to a pilot fuel (responsible for starting the combustion), i.e. the latter is introduced once the main fuel has been injected. The combustion of the main fuel is partially by pre-mix and partially by diffusion. However, at low loads the pilot fuel is injected in advance to the main fuel which burns by diffusion. This prior art engine is mainly intended to be applied to the use of diesel and natural gas; and needs to detect the engine load status in order to decide the order of injection. In comparison, the present invention reguires a pre-mixture of fuel and air, (i.e. indirect injection) as in a conventional petrol engine. When this mixture is burned, it produces engine power. Furthermore, the present invention has a simpler control regime (comparable to the same parameters that need to be known for spark generation) and simpler hardware (only one injector per cylinder is required whereas EP0643209 illustrates two) . It is acknowledged that the engine of the present invention recjires a fuel injector in the intake port to the or each cylinder to supply the primary fuel; but port injectors are simpler and cheaper than combustion chamber injectors, as they are exposed to considerably lower pressures and temperatures in use. As the fuel injector in the port supplies the primary fuel, it may be regarded as the primary injector. Air is mixed with injected primary fuel in the intake port in the conventional way, so that the primary fuel arrives in the cylinder as a fuel-air mixture, which would conventionally be ignited by one or more spark plugs.

Ihe present invention results in an improved petrol engine in terms of performance and emissions by addressing the way the flame front is created and propagated; rather than reguiring an entirely new engine tpe (hybrid), or an improved diesel engine.

An internal combustion engine according to the present invention will be described hereinafter by reference to the accompanying drawing, wherein:-Figure 1 illustrates a sectional view of an engine cylinder incorporating the invention.

As illustrated by Figure 1 a cylinder 11, bored into or formed in a cylinder block CB, includes conventional petrol engine features such as a piston 12, an air/fuel mixture intake port 13 with valve iSa, and an exhaust port 14 with valve l4a. The piston is illustrated at the top of its stroke, such that a combustion chamber 15 is effectively defined in the headspace of the cylinder 11. At least one piston ring 16 is provided to form an annular seal about the piston 12, and to isclate the combustion chamber 15 from the remainder of the cylinder 11.

The present invention is generally intended for incorporation into a petrol engine with conventional components and control systems, with the exception of the ignition system that will be described below.

According to the invention, an auxiliary fuel injector 17 is provided to penetrate through a boundary of the combustion chamber (which in the illustrated embodiment has a concave hemispherical ceiling surface), such that an auxiliary fluid fuel can be injected into the combustion chamber. Injector 17 is fed by a fuel line from a suitable reservoir (e.g. a secondary fuel tank) for the auxiliary fuel. The auxiliary fuel feed system is not illustrated and, likewise, conventional main fuel lines and exhaust systems are not illustrated.

By virtue of the extent of the projection of injector 17 into the combustion chamber 15, the shape of the injector nozzle, the nature of the fuel or a combination of all three of these factors, the auxiliary fuel preferably auto-ignites at a central point P in the combustion chamber 15. This ignition causes a second combustion in the chamber of the main fuel-air mixture previously introduced via intake port 13 in the conventional way. The petrol engine incorporating the invention otherwise operates in a normal four stroke sequence where ignition occurs after the piston has reached the top of its strcke, and the fuel-air mixture is therefore maximally cc mp r e s s e d.

By design and selection of the auxiliary fuel, the pressure of the compressed fuel-air mixture within the chamber is sufficient to ignite the auxiliary fuel; which in turn ignites the fuel-air mixture, and pushes the piston 12 downwards to drive a crankshaft (not illustrated) in the conventional way. On the upstroke of piston 12, exhaust valve 14a opens to allow combusted gas to escape. When piston 12 reaches the top of its stroke, intake valve l3a opens to enable a new charge of fuel-air mixture to be introduced to the chamber 15 by virtue of the downstroke suction of piston 12 or, potentially, by positive injection.

The subsequent piston upstroke compresses the fuel-air mixture. The auxiliary fuel is then injected to cause ignition and combustion.

One example of auxiliary fuel according to the invention is diethyl ether; which has a relatively low auto-ignition temperature. Only a small amount of such fuel is needed to trigger the combustion of the primary fuel-air mixture and hence, to drive the piston down. The auxiliary fuel does not need to contribute to the power output of the engine, as it simply replaces the need for a spark plug. Alternative auxiliary fuel types can be tested and implemented with the invention.

A typical petrol engine operates at about a 10:1 compression ratio, which at maximum compression is sufficient to ignite the auxiliary fuel. Preferably no additional heating or ignition method is needed to initiate the first cycle on engine start up; which will otherwise be by virtue of a conventional starter motor, used to crank the engine. The operating temperature in a petrol engine at high compression (but before combustion) is about 200°C.

With regard to injector (17) construction it is expected that a single hole, to deliver a concentrated charge of auxiliary fuel is preferred over a multiple hole ("mist") injector, as may be used in a diesel engine that intentionally delivers a distributed mist of fuel for primary combustion.

General timing and control aspects of the internal combustion engine of the invention can be determined according to known skill in the art. There is no minimum or preferred octane rating for the petrol fuel which may be used with the engine of the invention.

Although a monoblock or fixed head engine construction has been shown in the Figure for ease of illustration and understanding, the invention is equally applicable to an engine using a separate cylinder block and cylinder head, which are conventionally bolted together, the joint between block and head being sealed by a head gasket.

As previously mentioned, current petrol engines produce a spark close to the cylinder head such that: 1. The combustion flame front guickly contacts the cylinder head wall when propagating; and 2. The flame front takes a relatively long time to reach the mixture which is far from the spark (i.e. close to the piston edges) As a result, the first effect makes the flame locally extinguish due to heat losses (not enough temperature to self-maintain burning close to the walls) , losing thermal efficiency and increasing emissions; whilst the second effect results in a reduction of the maximum achievable pressure, due to the time reguired for the combustion to finish during the expansion cycle.

The purpose of the present invention is to improve combustion quality and speed, leading to a cleaner engine in terms of emissions; whilst increasing its performance (power and torgue) The invention consists of a petrol engine with a normal "making mixture" system (i.e. indirect multi-point injection into ports, etc.); but without a spark plug. Once the mixture is compressed as in a normal petrol engine cycle, there is a direct injection system for each engine cylinder such that a "secondary" fuel is injected that is able to self-burn under the prevailing combustion chamber pressure and temperature conditions, so that it causes the combustion chamber mixture of primary fuel and air to commence combustion.

The main difference with regards to a spark plug engine is that instead of starting the flame front on a region proximate to a metallic boundary of the combustion chamber (around the spark plug electrodes), the flame front corresponds to the perimeter of the volume occupied by the direct "secondary" injected fuel thus (similarly to a diesel engine) leading to a more homogeneous, quick, and complete combustion.

Although terms such as "ceiling" have been used to describe components in suoh a way as to imply that the cylinder block is mounted upright and that the pistons reciprocate vertically, the invention is equally applicable to an engine with canted or horizontal cylinders.

Claims

WHAT WE CLAIM IS: 1. An internal combustion engine including: at least one cylinder in a cylinder block; a piston mounted for reciprocating movement within the cylinder; a combustion chamber defined by the free volume in the cylinder when the piston is at the top of its stroke; an intake or injector port for supplying a fuel-air mixture to the combustion chamber; an exhaust port for removing exhaust gas from the combustion chamber; and an auxiliary fuel injector for supplying an auxiliary fuel into the combustion chamber that will auto-ignite when the fuel-air mixture is compressed.
2. The internal combustion engine of claim 1, wherein the combustion chamber is bounded by the piston and by plural surfaces of the cylinder.
3. The internal combustion engine cf claim 1, wherein the engine comprises a cylinder head corresponding to the at least one cylinder, said cylinder head being fastened to said cylinder block and sealed thereto.
4. The internal combustion engine of claim 3, wherein the combustion chamber is bounded by the piston, the cylinder walls, and the cylinder head.
5. The internal combustion engine of any preceding claim, wherein the combustion chamber is a monospace.
6. The internal combustion engine of any preceding claim, wherein the auxiliary fuel injector is arranged for injecting the auxiliary fuel towards the centre of the combustion chamber.
7. The internal combustion engine of claim 6, wherein the auxiliary fuel injector projects substantially into the combustion chamber in order to supply auxiliary fuel to the centre of the combustion chamber.
8. The internal combustion engine of claim 6 or 7, wherein the auxiliary fuel injector has a nozzle that is shaped in order to supply auxiliary fuel to the centre of the combustion chamber.
9. The internal combustion engine of claim 8, wherein the auxiliary fuel injector has a nozzle with a single hole.
10. The internal combustion engine of any preceding claim, configured for use with petrol fuel as a primary source of power.
11. The internal combustion engine of claim 10, wherein the auxiliary fuel is diethyl ether.
12. A method of igniting a primary fuel of an internal combustion engine including the step of providing an auxiliary fuel to a combustion chamber via an injector, wherein the auxiliary fuel is combustible at the temperature and pressure of a compressed mixture of primary fuel and air.
13. The method of claim 12, wherein the auxiliary fuel is injected substantially to a centre of the combustion chamber.
14. The method of claim 13, wherein injection to the centre of the combustion chamber is achieved by virtue of the extent of projection of the injector into the combustion chamber, the shape of a nozzle of the injector, the nature of the auxiliary fuel, or a combination of more than one of these factors.
15. The method of any of claims 12 to 14, wherein the primary fuel is petrol, and is utilised as a petrol-air mixture for combustion in the combustion chamber.
16. The method of any of claims 12 to 15, wherein the auxiliary fuel is diethyl ether.
17. A petrol internal combustion engine, substantially as herein described with reference to the accompanying drawing.
18. A method of igniting the primary fuel of an internal combustion engine, substantially as herein described with reference to the accompanying drawing.