NZ196916A - Metering gaseous fuel to compression ignition engine - Google Patents

Description

156016 NEW ZEALAND PATENTS ACT, ]955 No.: 136,916 Date: 23 June 1981 COMPLETE SPECIFICATION "DUAL FUEL SYSTEM FOR COMPRESSION IGNITION ENGINE" ^ We, WARRICK DONALD LAING, of 34 Fisher Street, Johnsonville, New Zealand, a New Zealand citizen, and GAIL FRANCES PRICHARD, of 6 Perry Street, Silverstream, Upper Hutt, Wellington, New Zealand, a New Zealand citizen, as administratrix of the estate of the late ALAN RAYMOND PRICHARD, previously of 4 Wyndham Road, Pinehaven, Upper Hutt, New Zealand, a New Zealand citizen, hereby declare the invention for which we pray that a patent may be granted to and the method by which it is to be performed, to be particularly described in and by the following statement:- (followed by page la) 196916 A COMPRESSION IGNITION ENGINE This invention relates to a system of gas fuelling of compression ignition engines preferably of the high-speed type. These engines would predominantly be in automotive applications fuelled by CNG and diesel.

The problem this invention aims to overcome is to provide a way of controlling the gas and diesel fuelling of engines, when operating in a dual fuel mode, in such a way as to provide satisfactory and efficient operation of these engines. A secondary problem the invention aims to overcome is that of being able to retrofit the control system to existing engines.

An object of the invention is to provide a means of gas fuelling which contains the desirable features of retention of the volumetric and thermodynamic efficiency of the engine coupled with the simplicity of design and maintenance of manifold admission of the gas fuel.

In addition, the related problem of control of detonation in the gas fuelled engine is provided for by wide variation of the air to gas ratio.

A further object is to provide a system that is basically fail-safe. Some of the benefits of satisfying this requirement should permit compliance with CNG vehicle installation regulations without the use of ancillary equipment.

Accordingly the present invention consists in a compression ignition engine having a pilot liquid fuel feed to the 196916 engine and a separate gaseous fuel feed characterized in that the separate gaseous fuel feed is controlled by means controlled by hydraulic pressure dependent on engine speed and/or engine load.

Preferably said means controlling said separate gaseous fuel feed is a valve.

Preferably said valve is a piston type valve.

A1 ternativelysaid valve xs a diaphragm type valve. i Preferably for any engine speed when the engine is running the hydraulic pressure has a predetermined maximum value there being bleeding off circuitry to enable reductions of hydraulic pressure below said maximum value for the engine speed.

Preferably means is provided whereby under low load conditions engine speed governor means cause the bleeding off circuitry to cause a reduction in hydraulic pressure and hence gaseous fuel feed for the particular engine speed.

Preferably said hydraulic pressure is dependant on engine speed and the means which controls the separate gaseous fuel feed is a regulator valve dependant on such hydraulic pressure, said regulator valve and the hydraulic pressure being arranged such that there is no flow of said separate gaseous fuel feed when the engine is not running.

In a further aspect the invention consists in a compression ignition engine of a Icind having a pilot liquid fuel feed into each combustion chamber and having a gaseous fuel feed to each combustion chamber characterized in that there is provided: 2 1SG316 means dependant on engine speed to generate a hydraulic pressure which increases with engine speed, means to govern the effect of load on any engine speed, means responsive to said means to govern to reduce said hydraulic pressure in low load situations to result in a t resultant hydraulic pressure less that otherwise would be the case, and means dependant on said resultant hydraulic pressure to control the feed of said gaseous fuel, the arrangement being such that when the engine is not running said means dependant on said resultant hydraulic pressure does not allow a gaseous fuel feed and such that for any speed there is a corresponding feed rate of gaseous fuel dependent on said resultant' i hydraulic pressure, the greatest gaseous feed for any engine speed being that when the engine is under load sufficient to minimize the reduction of said hydraulic pressure by said means responsive to said means to govern.

Preferably said means to govern is a mechanical governer, or alternatively a.hydraulic governor, the mechanical movement of: which is constrained from adjusting the liquid fuel feed and instead arranged to coact with said means responsive to said means to govern.

Preferably said gaseous feed J- is into the inlet manifold or manifolds of the engine.

Preferably said means responsive to said means to govern is a bleeding circuit.

In«yet a further aspect the present invention consists - 3 196916 in a fuel system for a compression ignition engine which results in a compression ignition engine in accordance with the present invention. The present invention also consists in componentry for retrofitting .to a compression ignition engine (preferably a governed compression ignition engine) to provide a compression ignition engine in accordance with the present invention.

Preferred forms of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a flow diagram showing part of the componentry in accordance with the present invention, T designating a diesel or other liquid fuel tank, P designating a fuel pump, V designating a change over valve, G designating a governor , G.F. designating a gaseous fuel supply, R designating a regulator which is the preferred form of valve in accordance with the present invention, and E designates the engine and preferably the engine manifold to receive the gaseous fuel flow, components P and R being shown diagrammatically in section, Figure 2 is a diagrammatic view of a hydraulic governor having the accelerator linkage designated as A and the flow into the governor being designated by an arrow, the flow out from the governor being designated by an arrow and the two-way flow also designated by arrow between the governor and ^TeaT^ // ' o 4 V 156516 the regulator e.g., R of Figure 1, Figure 3 is a governor valve sensing mechanical movement of the engines ceutrifugal governor to provide the bleeding wanted in low load situations again with the arrows designating the same features and Figure 4 shows an alternative governor valve to that of Figure 3 again sensing mechanical movement of the engine's centrifugal governor to provide the bleeding wanted in low load situations, again with the arrows designating the same features.

The preferred forms of the present invention were designed to meet the afore mentioned objects 1. Not having restrictive carburettor parts in the air way facilitates maintenance of volumetric efficiency and retains simplicity of manifold admission. 2. Control of detonation is necessary to limit the pressure rise in the cylinders and hence the point of peak pressure relative to TDC. This is obtained by tive compression ratio or exhaust gas recirculation for dilution control of the flame propagation rate or fitment of or modifications to variable ignition timing were not favoured as they involve loss of thermodynamic efficiency and greater modifications to the engine. 3. Auto-ignition of the pilot injection of diesel fuel provides sufficient energy to ignite the lean gas mixes used. This ignition system yields hundreds of times more energy 1' (i) knock resistance of the fuel related to the high auto-ignition temperature of a methane mixture such as CNG, (ii) control of flame propagation rate by use of a lean mixture.

Other means such as throttling to reduce the effec- spark system. 4. In variable speed applications.some loss of torque or lugging power at low revs on dual fuel or in constant speed applications a transitory engine overload on dual fuel can be overcome by reversion to a higher percentage of diesel under these conditions. Equally it is possible to trim back the percentage of diesel at higher revs.

The fail-safe constraints were as follows 1. Engine stop shuts the gas flow off positively as hydraulic pressure is lost in the control system. 2. Flooding prevention is provided as hydraulic pressure in the control system is slow to build up on starting. 3. Simplicity is achieved by the use of small bore gas plumbing, between the regulator and the engine , at the higher than usual pressures so that accurate orifice metering of the gas flow is possible as the pressure varies with engine revs and load. The same high pressure and small bore line allows the regulator to be mounted remotely from the manifold with no significant loss of response. 4. Simplicity is also achieved by allowing the changeover valve for diesel/dual fuel to be manually or electrically controlled as the installation requires. 1369t6 The invention also consists of apparatus for providing such feed(s) and/or control and various conversion methods.

Basically the system described involves the metering of gas to the inlet manifold of the engine by hydraulic servo-control of a gas pressure regulator. Hydraulic fluid, which may be a fuel with the desired property of low viscosity, such as diesel, is admitted to one side of the regulator diaphragm to balance gas pressure on the other side. System control is therefore primarily obtained in the hydraulic fluid circuit although final adjustment of gas flow is by an adjustable metering orifice.

For variable speed engines the system is described as follows below. A fixed displacement hydraulic pump driven by the engine in combination with a bleed orifice produces an output pressure related to engine speed. For certain rotary fuel injection pumps as fitted to these engines this variable pressure may be tapped directly from its transfer pump. This output is led via a valve, the purpose of which is to change over from operation on diesel fuel to gas/pilot fuel operation and thence via a governor valve for speed control of the engine to one side of the pressure regulating valve. Gas pressure produced in the regulator is thus in balance with the pressure output of the said hydraulic oil pump unless the governor valve is shut and is therefore related to the engine speed. By virtue of the pressure related flow characteristics through the gas metering orifice maximum gas fuel to the engine at any given speed is determined for control of combustion chamber detonation. Under engine acceleration conditions - restrictive damping of the hydraulic line between the governor assembly and the regulator may be used to control combustion chamber detonation. Figure 1 of the accompanying drawings outline the system in the manner of a flow chart.

For constant speed engines the control system is able to be constructed more simply by connecting the governor valve to the engine lubrication oil pressure supply. The system as described a"bove can then be adjusted to give the appropriate gas fuelling for the oil pressure available. A restrictor orifice ensures a minimum bleeding off of the lubrication oil.

For engines consuming gas from a low pressure supply, normally constant speed engines fuelled by producer gas or biomass digestor gas of suitable calorific value, the control system is described as follows. A constant pressure lubrication oil supply is used as noted above. A changeover valve and governor valve are incorporated. A pressurising fan such as a centrifugal compressor type fan is required to yield a positive pressure at the regulator valve by drawing gas through a pipe from the gas generator. The pressure regulating valve is of a different type and would comprise either a large bore regulator valive as diagrammed or a butterfly valve in the gas admission pipe under hydraulic control.

-.With reference to the operation of the governor and the pilot fuel control two systems are used.

Firstly a system has been devised in which the existing engine fuel control mechanism is restrained in the pilot fuel position mechanically, or by use of a solenoid or a small pressure-operated ram and the existing engine governor is not used for speed control. The speed related output pressure of the system pump is used in a hydraulic governor valve one form of which is shown in Figure 2. Here hydraulic pressure moves a control piston against spring pressure determined by the accelerator position to produce a reduced pressure in the static line between the governor 9 19(>$l6 valve and the gas pressure regulator. That reduced pressure is related to the demand requirements for engine speed.

Secondly a system has been devised in which the speed related hydraulic pressure of the pump is only used to control maximum fuelling of the engine and governing is obtained by the action of the engine's own centrifugal governor or hydraulic governor with a mechanical movement on a small hydraulic valve. Restraint of the engine's fuel control rack or equivalent is obtained by action of a small hydraulic piston two forms of which are shown in Figures 3 and 4, These have shut-down piston and governing valve combined into one unit. Admission of fuel oil pressure by the changeover valve causes the piston to move forcing the control rack to move to the pilot fuel position which may be variable according to engine speed as determined by a stiff spring. Movement of the piston to the pilot fuel position uncovers a port admitting governor control pressure to the static line between the governor valve and the gas pressure regulator. The movement of the engine's fuel control rack to operate the governor valve is confined to a small range about the pilot fuel position. On some engines on which heavy overload cannot be sustained on gas , provision is made for the fuel control rack force to overcome the force on the piston which returns the engine to diesel operation until the load reduces.

For constant speed engines a pressure as set for that engine can be used rather than a speed related hydraulic pressure as noted above. The descriptions of the operation of 106916 the governor and the pilot fuel control in both systems is unchanged however.

On the basis of the foregoing the many advantages of the present invention can readily be seen, for example, it can be seen that by using a small diesel or other liquid fuel pilot feed CNG or other combustible gas can be effectively employed in a wide range of engine usages without the drawbacks of most pre-existant systems. Also it can be seen that the choice of a higher than usual gas delivery pressure would permit a number of advantages including (i) small bore plumbing with overall size reductions, (ii) small physical size of the gas regulator allowing precise control, (iii)remoteness of the gas regulator from the manifold, (iv) with high flows gas expansion is less so cooling effects are reduced.

It can also been seen that the use of hydraulic control circuitry reduces the need for engine model specific parts in control linkages.

It can also be seen that the use of control within the hydraulic circuit itself yields the following benefits:- (i) the need is obviated for low friction gas tight seals, (ii) any failure or loss of control pressure makes the system failsafe.

It can also be seen that the provision for control of the amount of pilot fuel permits (i) the governor to allow the engine to lapse back onto P P i ii & 196916 diesel under heavy overload, (ii) variation of pilot injection with engine speed particularly to compensate for variations of injection pump efficiency at different speeds.

It is believed therefore that the present invention in the form as claimed or the more preferred form hereinbefore described should find wide spread acceptance. " - 196916

Claims (12)

WHAT WE CLAIM IS:

1. A compression ignition engine havinga pilot liquid fuel feed to the engine and a separate gaseous fuel feed characterized in that the separate gaseous fuel feed is controlled toy means controlled toy hydraulic pressure dependent on engine speed and/or engine load.

2. An engine as claimed in claim 1 wherein said means controlling said separate gaseous fuel feed is a valve.

3. An engine as claimed in claim 2 wherein said valve is a piston type valve.

4. An engine as claimed in claim 2 wherein said valve is a diaphragm type valve.

5. An engine as claimed in any one of the preceding claims wherein for any engine speed when the engine is running the hydraulic pressure has a predetermined maximum value there being bleeding off circuit ry; to enable reductions of hydraulic pressure below said maximum value for s.aid engine speed.

6. An engine as claimed in claim 5 wherein means is provided whereby under low load conditions engine speed governor means cause the bleeding off circuitry |to cause a i reduction in hydraulic pressure and hence gaseous fuel feed for the particular engine speed.

7. An engine as claimed in any one of the preceding claims wherein said hydraulic pressure is dependent on engine speed and the means which controls the separate gaseous fuel feed is a regulator valve dependent on such hydraulic pressure, said regulator valve and the hydraulic - 13 i- OECV)85 ; 10691$ pressure being arranged such that there is no flow of said separate gaseous fuel feed when the engine is not running.

8. A compression ignition engine of a kind having a pilot liquid fuel feed into each combustion chamber and having a gaseous fuel feed to each combustion chamber characterized in that there is provided means dependent on engine speed to generate a hydraulic pressure which increases with engine speed, means to govern the effect of load on any engine speed, means responsive to said means to govern to reduce said hydraulic pressure in low load situations to result in a resultant hydraulic pressure less that otherwise would be the case, and means dependejnt on said resultant hydraulic pressure to control the feed of said gaseous fuel, the arrangement being such that when the engine is not running said means i dependent on said resultant hydraulic pressure does not allow a gaseous fuel feed and such that for any ' speed there is a correspond!ng feed rate of gaseous fuel dependent on said resultant hydraulic pressure, the greatest gaseous feed for any engine speed being that when the engine is under load sufficient to minimize the reduction of said hydraulic pressure by said means responsive to said means to govern.

9. An engine as claimed in claim 8 wherein said means to govern is a mechanical governor constrained from adjusting the liquid fuel feed and instead arranged to coact with said means responsive to said means to govern. *-7;> m f.;

10. An engine as claimed in claim 8 or claim 9 wherein said gaseous feed is into the inlet manifold or manifolds of the engine.;

11. An engine as claimed in any one of claims 8 to 10 wherein said means responsive to said means to govern is a bleeding circuit.;

12. An engine as claimed in any one of the preceding claims substantially as hereinbefore described with reference to any one, some or all of the accompanying drawings. —-c— _;i) ^ day of;DATEDTH1! \ park & SON;A- " i O n;PI* ,«,NT= ^ p ipPLtCA!"' agents fob the afp - 15 -