Internal-combustion engines – Combustion chamber means having fuel injection only – Injection of fuel onto igniter – deflector – heater – or atomizer
Patent
1999-09-14
2000-11-21
Solis, Erick
Internal-combustion engines
Combustion chamber means having fuel injection only
Injection of fuel onto igniter, deflector, heater, or atomizer
123305, F02B 302
Patent
active
061487929
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a spark ignition internal combustion engine having direct injection of liquid fuel into each engine cylinder.
Direct injection spark ignition engines are advantageous in that they may be run with a homogeneous charge for high load operation as well as a stratified charge for lean burn or part load operation. For homogeneous charge, the fuel can be injected early in the cycle (when the piston is near the bottom of its stroke) and is mixed well with the air before it is ignited. For stratified charge, on the other hand, it is necessary to inject later in the cycle when the piston is nearer the top of the compression stroke so that the fuel does not have sufficient time to mix with the air before it is ignited. This mode of operation, however, has certain problems in that fuel injected late in the cycle is deposited on the piston and unavoidably wets the piston surface. The fuel adhering to the surface of the piston is difficult to burn because it is not well mixed with air and for this reason it causes high hydrocarbon and soot emissions. If fuel is injected earlier in the compression stroke to reduce wetting of the piston, the spark timing must also be advanced in order to ignite an ignitable region of the stratified charge and the thermodynamic efficiency of the engine could suffer because the heat release could occur too early compared with the optimum timing for maximum power.
A further disadvantage of the conventional combustion chamber design employed in direct injection engines is that the fuel spray is aimed away from the spark plug in order to avoid wetting the spark plug electrodes and when a stratified charge is to be achieved it is difficult to ensure that an ignitable region is present in the vicinity of the spark plug.
It has been proposed in U.S. Pat. No. 5,421,301 to place one or more injectors in the side wall of the cylinder within the area of the cylinder bore swept by the piston rings and to aim the spray towards the cylinder head, rather than the piston, in particular towards the exhaust valve. The injectors in this patent are low pressure injectors and need to be isolated from the combustion chamber by the piston at the top of the compression stroke and injection can only therefore take place during the intake stroke or at the latest at the start of the compression stroke. The aim of the invention is to vaporise the fuel using the heat of the exhaust valve. The disadvantage of this proposal is that because of the fuel vaporisation by an early stage in the compression stroke the engine can only be operated with a homogeneous charge. The advantages associated with a stratified charge, for which direct injection should excel, cannot be realised using this proposal.
It has also been proposed in U.S. Pat. No. 5,233,956 to position the fuel injector in the cylinder head in such a way that while the fuel spray is aimed towards a cavity in the piston to create a charge when injected during the compression stroke, it is also aimed at the rear face of an intake valve when the intake valve is above a predetermined lift position when injected during the intake stroke. The intention is for the fuel spray to impinge on the rear face of the intake valve and to bounce back into the intake port before being drawn into the combustion chamber. The fuel injector is operated at a pressure in excess of 70 kg/cm.sup.2 in order to ensure the fuel spray impinges with force on the valve in order to bounce off the valve. Such an arrangement is effective in allowing a large quantity of fuel to be introduced into the combustion chamber without risk of excessively wetting the piston. On the other hand, because the fuel spray is deliberately arranged to impinge on the rear face of the intake valve, the valve itself will inevitably be wet with fuel.
Wetting of the intake valve is not desirable for several reasons. First, the rate of evaporation of the liquid fuel film is significantly lower than that of very fine fuel droplets because of the much smaller surface area. Second, any liqui
REFERENCES:
patent: 2800118 (1957-07-01), Scherenberg
patent: 5357925 (1994-10-01), Sasaki
patent: 5735240 (1998-04-01), Ito et al.
Drouillard Jerome R.
Ford Global Technologies Inc.
Solis Erick
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