CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of US Provisional Applications No. 61224900 filed on July 12, 2009, the contents of which are

incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to combustion methods, and an internal combustion engine using the same, either compression ignition or spark ignition, or mixed-mode combustion engine using both compression ignition and spark ignition.

2. Description of the Related Art

While the engine industries have put great efforts for Homogenous Charge

Compression Ignition (HCCI) and Premixed Charge Compression Ignition (PCCI) combustion, the conventional multi-hole fuel injector limits the operation ranges of HCCI and PCCI and flexibility for combination of different combustion modes in the same engine power cycle. The major reasons are the fixed injection spray angle and dense jet nature of conventional sprays. Since current HCCI or PCCI can only operate in low to medium loads in practical applications, conventional fixed- spray- angle nozzle designs have to be compromised for low and high loads. A larger spray angle for high loads will bring severe wall (cylinder liner) wetting issues for early injections dictated by

HCCiyPCCI mixture formation requirements. The major wetting issues are associated with high HC and CO emissions and lower combustion efficiency. A fixed narrower spray angle optimized for premixed combustion will generate more soot formation for high loads. Higher soot formation also reduces fuel efficiency. Thus, a variable spray angle or using different spray angel injection and penetration are much better positioned to solve this contradiction between the requirements for different injection timings and operation loads. The innovative design of said combustion method has solved this wall- wetting issue through providing a variable spray angle or using different spray angles, which is smaller for early injection and becomes larger for late injection, and a variable spray pattern or different spray patterns, which is formed with smaller holes with smaller spray angles for early injection with less penetration strength, and tends to larger multi- jets for late injection with higher penetration strength. Such a variable spray angle can be provide by either a fuel injector with variable orifice such as documented in

PCT7IB2005/051474. The said different spray angles and patterns can also be provided by two fuel injectors in a single cylinder with different fixed spray angles and nozzle hole layouts.

SUMMARY OF THE INVENTION

A adaptive mixed-mode combustion method, which is mainly for internal combustion engines, either compression ignition or spark ignition, or mixed-mode engines using both compression ignition and spark ignition. The said combustion method utilizes a variable orifice fuel injector or at least two injectors per cylinder wherein it has means to produce variable spray patterns with smaller spray angle multi-jets for earlier injection(s), and larger spray angle multi-jets for main injection(s) around engine top dead center, respectively, in the same engine power cycle, wherein it has adaptive means to distribute fuel into combustion chamber space based on engine loads and speeds, to produce a separate twin triangular heat release curves to effectively reduce emissions and fuel consumptions. A combustion engine using the said combustion method is also provided.

The innovative design of said combustion method has solved wall- wetting issue through providing variable spray angles or different spray angles, which are smaller for early injection(s) and becomes larger for late injection(s), and variable spray patterns, which are formed with smaller jets with smaller spray angles for early injection(s) with less penetration strength, and becomes larger multi-jets with larger spray angles for late injection(s) with higher penetration strength. The said combustion method can significantly reduce soot and nitride oxygen emission formation and fuel consumption.

A premixed charge of fuel and air is desirable for reducing emissions. However, for high engine loads, if all fuel and air is premixed before TDC, in the event of out of controlled combustion before TDC, the sudden release of all the heat could damage the engine. Thus, at high engine loads, only partially premix fuel and air before TDC is desirable. At the same time, in order to reduce emissions, an on-going 'premixing' process is desired. Thus, a novel method for introducing fuel into the combustion chamber space is desired to distribute partial fuel in desirable locations and prepare the fuel to join faster combustion reaction only close or after TDC. This is realized by distributing partial fuel in a fine mixture format close to chamber surface approximately between the middle stage of compression stroke and 40 degree before TDC.

Until recently, most internal combustion engines using open loop control due to lacks of in-cylinder pressure censor or other reliable sensor feedbacks. It is also due to the fact of the complexity associated with real time control and lacking of a simple effective guiding rules to dynamically adjust the key operating parameters such as fuel injection timings and quantity ratios. The look-up table which was predefined during engine calibration is not sufficient to adapt to real engine operating environment which generally different from calibration conditions. The simple criteria of setting the heat release centroid to an optimized predetermined crank angle provide a simple but yet effective means to optimize engine thermal efficiency in real time based on real time in-cylinder pressure measurement. The simple rule of separating the heat release of premixed combustion with that of main injection diffusion combustion forms an effective means to reduce NOx emissions due to the simple fact of reducing high temperature crank angle window due to high peak heat release.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an illustration of heat release for conventional diffusion combustion. Initial heat (11) release is associated with high NOx formation and is overlapped with main heat release (12).

Fig. 2 is an illustration of heat releases for said Adaptive Mixed-Mode Combustion method. First heat release (21) is associated with clean early premixed combustion, thus reduces diffusion combustion of main injection (22). The twin triangular heat release reduces emissions and provides more flexibility for thermal efficiency optimization. The vertical line (2C) is the Centroid line of heat release, which can be dynamically set to an optimized crank angle to optimize combustion.

Fig. 3 Exemplary hest release curves of a combustion engine using the said Adaptive Mixed-Mode Combustion method. Heat release from smaller earlier jets is separate from heat release from larger later fuel jets. Heat release from smaller jet and that from larger jet are separate sequential events, with heat release from smaller jet happens first, and that from larger jets follows. The separate heat releases form a twin triangular shape heat release curves.

Fig. 4 is an illustration of different spray patterns optimized for different injection timings, with earlier injections having smaller angles (2a) for premixed combustion, and late injection around TDC having larger spray angles (2c) similar to conventional diesel combustion. 41 and 42 - small angle sprays for premixed combustion; 43 - larger angle sprays for conventional combustion;

Fig. 5 is an illustration of the internal combustion engine using the said combustion methods and variable orifice fuel injectors; 51 - variable orifice fuel injector; 52 - small angle sprays for early or late injections away from TDC; 53 - piston chamber surface; 54 - piston, 55 - cylinder; 56 - cylinder head; 57 - larger angle sprays for main injections;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A adaptive mixed-mode combustion method for internal combustion engines, comprising steps of: (i) setting fuel injection timings and fuel quantities based on engine speeds and loads, (ii) utilizing at least one fuel injector which has means to introduce fuel into a combustion chamber with different fuel injection spray angles, with smaller spray angles for an early or post fuel injection, which is away from engine top dead center (TDC), and larger spray angles for a main fuel injection, which is close to engine TDC, respectively, in the same engine power cycle which typically includes intake,

compression, power and exhaust strokes; (iii) introducing fuel into a combustion chamber with at least one said early injection with a plural number of smaller jets with smaller spray angles, and with at least one said main injection with a plural number of larger jets with larger spray angles, and with an optional post injection after said main injection with a plural number of smaller jets, in the same engine power cycle respectively based on predetermined fuel quantity ratios, wherein it has adaptive means to selectively chose same or different spray patterns for early, main and post injections based on engine loads, speeds, and injection timings; (iv) dynamically adjusting injection timings for introducing the smaller fuel jets and larger fuel jets such that the accumulated heat releases from the smaller fuel jets and larger fuel jets are separate sequential events, with the heat release from all early smaller jets happens first and ends, then after the heat release from larger jets follows; (v) dynamically adjusting the fuel injection quantities for the smaller jets and larger jets such that the total fuel quantity from all the larger jets is equal or greater than all of the fuel from early injected smaller jets; (vi) dynamically readjusting fuel quantities and injection timings for the smaller and larger fuel jets such that the crank angle of the centroid of the separated heat releases from smaller fuel jets and larger fuel jets is close to a predetermined crank angle point which tends to maximize the engine thermal efficiency and minimize engine emissions. In embodiment, such a centroid of heat release can be calculated from the sampling of real time in-cylinder pressure censor and form a real time pressure curve, then calculate the heat release curves. Based on area below the heat release curves, we can easily calculate the centroid position of the twin heat releases. Then we can dynamically adjust the fuel injection timings and quantity of smaller earlier jets and that of larger main injections. The centroid is preferably set between 5-20 degree ATDC.

For the above said combustion method, where in the smaller fuel jets are coupled with lower injection pressure, preferably between 300-1000 bar, and larger fuel jets are coupled with higher injection pressure, preferably above 1200bar, wherein the different fuel pressure levels are provided by at least one of the following means including different cam profiles, different pressure common rail reservoirs, or local pressure amplification inside injectors;

In one exemplary internal combustion engine using said Adaptive Mixed-Mode Combustion method, has following integrated features:

a. for said engine at low to medium engine loads, with approximately 20-50% of total fuel dose injected as earlier fuel injection(s) with smaller jets with smaller spray angles between 50 to 120 degree approximately between 100-50 BTDC, and the rest of the fuel injected with larger jets with larger spray angles between 120 to 150 degree proximately between -5-40 degree ATDC, preferably starting between 0-15 degree ATDC;

b. for said engine at above medium to full engine loads, fuel is injected in the similar manner as (a) but with less fuel percentage of approximately 5-20% injected as earlier injection(s), wherein the percentage decreases along with increased loads; c. having a variable orifice fuel injector with 6 to 10 larger holes having larger spray angles, and 6 to 20 smaller holes with smaller spray angles;

d. Said engine has an exhaust gas recirculation (EGR) ratio approximately between 5-60%, depending on engine loads, with lower loads tend to have higher EGR ratios.

e. wherein it has a compression ratio approximately in the range of 14-18, and a low swirl ratio approximately in the range of 0-1.5;

In another exemplary internal combustion engine using said combustion method, has following integrated features:

a. for said engine at low to around medium loads, with approximately 20-50% of total fuel dose injected as earlier injection with a nozzle having hole diameter approximately 70-120 micron meter within 100-50 degree BTDC, and the rest of the fuel injected approximately between -5-40 degree ATDC, preferably starting injection at 0-15 degree ATDC with a separate larger nozzle having hole diameters approximately 100-250 micron meter, depending on engine bore diameters;

b. for said engine at above medium to full engine loads, fuel is injected in the similar manner as (a) but with less fuel percentage of approximately 5-20% injected as earlier injection(s);

c. said engine has a lower swirl ratio preferably between 0-1.5, a preferred

compression ratio of 14 tol8;

d. said engine has a nozzle with 6-10 larger holes with larger spray angles

approximately 120-150 degree, and a separate nozzle with 6-20 smaller holes with smaller spray angles approximately 60-120 degree. The two separate nozzles are mounted in the same engine cylinder;

e. said engine has an exhaust gas recirculation (EGR) ratio approximately between 5-60%, depending on engine loads, with lower loads tend to have higher EGR ratios.