Premix Combustion Methods, Devices and Engines Using the Same

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of US Provisional Applications No. 60988941 filed on Nov. 19, 2007, 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, devices, and an internal combustion engine using the same, either compression ignition or spark ignition, or mixed-mode 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 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-area 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 HCCI/PCCI mixture formation requirements. The key wetting issues are associated with high HC and CO emissions and lower combustion efficiency. A fixed narrower spray angle optimized for premixing will generate more soot formation for high loads. Higher soot formation also reduces fuel efficiency. Thus, a variable spray angle 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 and devices has solved this wall-wetting issue through providing a variable spray angle, which is smaller for early injection and becomes larger for late injection, and a variable

spray pattern, which is formed with smaller holes with smaller spray angles for early injection with less penetration strength, and becomes larger multi-jets for late injection with higher penetration strength. Such a variable spray fuel injector was documented in PCT7IB2005/051474.

Mixture formation is most critical for PCCI combustion. The essential feature of PCCI is 'premixed charge', thus the in-cylinder equivalence ratio distribution is the most critical factor deciding engine emissions and performance. Currently practices indicated that, for HCCI and PCCI combustion, only low to moderate loads are practical to deploy HCCI or PCCI due to difficulty in controlling combustion starting point and pressure rise rate. Thus, an effective method to control the combustion reaction rate is important to extend the HCCI or PCCI operation maps.

SUMMARY OF THE INVENTION

The innovative design of said combustion method and devices has solved wall- wetting issue through providing variable 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 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 certain amount of fuel in desirable locations and prepare the fuel to join faster combustion reaction only after TDC. This innovative method is realized by distributing fuel on the chamber surface uniformly in the format of very small discrete fuel droplets (micro-dew format) approximately in the middle stage of compression stroke. Since fuel distributed in micro-dew format needs longer time to

evaporate, majority of the fuel will join faster reaction after TDC. But since the fuel in micro-dew format is formed by uniform distribution of micro droplets, after mixture ignition in combustion chamber space, the micro-dew fuel still can be quickly evaporated and become vapor to join faster reaction, thus it reduces conventional diffusion combustion. This method solves the contradiction of making fuel premixed and high pressure rise rate. This method of distributing fuel turns the 'premixed' combustion into a 'premixed' plus 'premixing' combustion, thus gives better control for combustion reaction rate and pressure rise rate. In another word, it turns into a desirable premixed combustion into a pre-conducted and on-going mixture forming process without the limitation of excessive pressure rise concerns, at the same time, eliminated or substantially reduced diffusion combustion.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an illustration of variable orifice fuel injector nozzle holes distribution patterns.

Fig. 2 is an illustration of variable orifice fuel injector opening process.

Fig. 3 is an illustration of early fuel injection and dew-film formation. 31- variable orifice fuel injector; 32 - center line of spray; 33 - small angle spray; 34 - piston top; 35 - micro-dew formation; 36 - swirl and squish flow; 2a - small spray angle;

Fig. 4 is an illustration of the said control method for variable sprays with the variable orifice fuel injector. Different signal widths give different needle lift time span and different spray patterns at different injection timings, with earlier injections having smaller angles (2a, 2b) for premixed combustion, and late injection around TDC having larger spray angles (2c) similar to conventional diesel combustion in the same engine cycle; 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

1. A combustion method, which is mainly for internal combustion engines, comprising steps of: (i) determining fuel injection timings based on engine speeds and fuel injection quantities or engine loads, (ii) utilizing a fuel injector composing a variable orifice nozzle, such as described in PCT/IB 2005/051474, (iii) providing variable spray angles with smaller spray angles for early or post fuel injection(s), which is(are) away from engine top dead center (TDC), and larger spray angles for main fuel injection(s), which is(are) close to engine TDC, respectively, in the same engine power cycle (which includes intake, compression, power, and exhaust stokes); (iv) providing variable spray patterns through different grouped fuel channel distributions (refer to Figure 1, 2) for a plural number of jets with smaller angles for said early fuel injection(s) and a plural number of jets with larger angles for said main fuel injection(s), in the same engine power cycle respectively, wherein it has adaptive means to selectively chose same or different spray patterns such as spray shape, size and distribution for early, late and main injections to distribute fuel into combustion chamber space based on fuel injection quantities or engine loads and injection timings; (v) providing variable spray exit area?, based on engine loads and speeds through selectively opening and closing a plural number of groups of micro fuel channels with different diameters or cross section areas to discharge fuel into combustion chamber, thus providing adaptive fuel injection flow rate for different engine loads and speeds. Refer to Figure 2, 3, 4, 5.

2. A combustion method of as described in above paragraph 1, which is mainly for internal combustion engines, which has means to uniformly distribute fuel in micro- dew shape droplets with majority of diameters being under 20 micron meter on the surface of the combustion chamber on piston top for fast evaporation after top dead center, with smaller spray angles approximately in the range of 40-100 degree, and the fuel injection for micro-dew formation occurs preferably between 120-50 degree

BTDC, depending on engine bore diameter and compression ratio, with smaller bore diameters and larger compression ratios intend earlier injections for dew-film formation. Refer to Figure 3.

3. A control method for controlling spray patterns of the said fuel injector in paragraph 1 through controlling its needle lift wherein it has means, preferably with dual-springs and flow networks for two- staged lifts or direct needle control, for varying sprays from multi-jets with smaller spray angles to multi-jets with larger spray angles selectively and continuously. Refer to Figure 2 and Figure 4.

4. A combustion method of paragraph 1, wherein it has a variable spray angle approximately between 50 -120 degree for said early or late fuel injection(s) which is away from engine TDC, and a variable spray angle of approximately between 120-150 degree, preferably around 140 degree, for said main fuel injection(s) closing to engine TDC;

5. A combustion method of paragraph 1, wherein it has single injection or a plural number of earlier injections with injection conducted approximately between 120-30 degree before TDC (BTDC) with multi-jets having smaller angles, and at least one main fuel injection conducted approximately between -10-30 degree after TDC (ATDC), preferably starting at 0-15 degree ATDC, with multi-jet sprays having larger spray angles. Refer to Figure 4.

6. An internal combustion engine using the combustion methods or devices as described in above paragraph 1, 2, 3, 4, 5 individually or collectively having means to distribute fuel, to control pressure rise rate, to control quantity of fuel for premixed mixture formation for adaptive premix combustion for different engine speeds and loads;

7. An internal combustion engine as described in paragraph 6, wherein it has a compression ratio preferably in the range of 14-18, and a low swirl ratio preferably in the range of 0-1.5;

8. An internal combustion engine as described in above paragraph 6, has following integrated features: a. for said engine at low to medium engine loads, with approximately 20-60% of total fuel dose injected as earlier fuel injection(s) approximately between 100-50

BTDC, and the rest of the fuel injected proximately between -10-30 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;

9. An internal combustion engine as described in above paragraph 6, has following integrated features: a. for said engine at low to around medium loads, with approximately 20-60% of total fuel dose injected as earlier injection with nozzle hole diameter approximately 70-100 micron meter within 100-50 degree BTDC, and the rest of the fuel injected approximately between -10-30 degree ATDC, preferably starting injection at 0-15 degree ATDC with larger nozzle hole diameters approximately 100-180 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. using a variable orifice fuel injector with at least two-row holes with different angles wherein the different rows of holes can be opened selectively; e. said variable orifice fuel injector has 6-10 larger holes with larger spray angles approximately 120-150 degree, and 6-20 smaller holes with smaller spray angles approximately 60-120 degree;

10. An internal combustion engine using the combustion method as in described in paragraph 2, wherein the quantity of fuel in micro-dew format distributed on combustion chamber surface increases along with the increase of engine loads, and the first injection timing advances along with the increase of engine loads, wherein the fuel distributed as micro-dew format on the combustion chamber surface on piston top is preferably less than 20% of the total injected fuel in the power cycle.