JP2930457B2 - Low cetane fuel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber and a fuel injection system of a diesel engine using a low cetane number fuel.

[0002]

2. Description of the Related Art When a low cetane number fuel is used for a diesel engine, it is necessary to ignite using a forced ignition device because of its poor self-ignition property. As shown in FIG. 7, when low cetane fuel is injected from the injection valve 01 into the combustion chamber A recessed at the top of the piston 03, when the initially injected fuel spray reaches the glow plug 02, the glow plug Then, the fuel spray injected subsequently self-ignites and burns rapidly because the gas temperature and pressure in the combustion chamber are sufficiently high.

[0003]

In the prior art, when low cetane number fuel is started to be injected from the injection valve 01, the fuel spray reaches the glow plug 02 and is immediately ignited by using the glow plug 02 as a heat source to reach combustion. This indicates that the period from the start of the injection to the ignition is short, and the combustion ends while the fuel spray is not sufficiently diffused throughout the combustion chamber. Therefore, in addition to the poor air utilization, or generate black smoke, there are problems such as many emission of nitrogen oxides NO _x,
Since combustion occurs at a specific position in the combustion chamber, the surface temperature distribution of the piston becomes uneven, and there is a problem that the piston is often cracked and damaged by thermal stress.

[0004] An object of the present invention is to solve the above-mentioned problems and to provide an HC
Well as and NO _x and soot, etc. failure due to thermal stress can be reduced emissions of harmful combustion products to provide a diesel engine using a low-octane fuel can be suppressed.

[0005]

According to the low cetane number fuel engine of the present invention, in a direct injection type diesel engine having a combustion chamber recessed at the top of a piston, an injection port 1A is provided from a lower surface of a cylinder head B to a combustion chamber side. , A main injection valve 1 having a multi-injection nozzle slightly projecting, a spray guide hole C formed in a trumpet shape from the inside of the cylinder head toward the combustion chamber, and an injection port located in the back of the spray guide hole. And a glow plug 3 attached such that a heating portion protrudes into the trumpet-shaped spray guide hole.

[0006] The present invention also provides a main injection valve 1 in addition to the above.
The fuel injection system is set so that the fuel injection is started sufficiently before the injection valve 2 for ignition. Δθ is the angle of the preceding injection, θ is the crank angle, and the symbol minus indicates the value before the top dead center. For example, when Δθ: main injection leading angle (deg) θ _FB : injection start timing (deg) of the ignition injection valve, the following equation is satisfied. (−2 / 15 × θ _FB + 8 °) ≦ Δθ ≦ (−10 / 15 × θ _FB + 20 °) However, −15 ° ≦ θ _FB ≦ 0 °

[0007]

The present invention operates as follows because the present invention is configured as described above. Since the main injection valve is a multi-injection nozzle and starts injection before the ignition injection valve in the entire operation range, a large number of main sprays are first formed in the combustion chamber according to the number of injection ports, and then slightly later. The fuel spray injected from the ignition injection valve is forcibly ignited by the glow plug in the trumpet-shaped spray guide hole and jets into the combustion chamber. This ignites the main spray that has sufficiently diffused into the combustion chamber, leading to combustion of the entire main spray. That is, according to the present invention, the injection in which the ignition spray is formed is performed at a time when the main spray is sufficiently diffused throughout the combustion chamber by the preceding injection,
Air utilization is improved. In addition, the main injection valve is arranged in a center injection format, and the number of ignition sprays is selected according to the number of main sprays, or the number of ignition sprays and injection timing are selected according to the size of the combustion chamber Therefore, the combustion performance and the exhaust gas characteristics are improved, and the piston has a variation range of the preceding injection that can make the piston surface temperature uniform.

FIG. 4 shows the injection timing of the main injection valve and the ignition injection valve. Here, Q _N : main spray injection amount, θ _M : main spray injection period, θ _MB : main spray injection start timing Q _F : ignition spray injection amount, θ _F : ignition spray injection period,
θ _FB : ignition spray injection start timing Q _F / (Q _F + Q _M ) ≦ 0.15 according to this definition
FIG. 5 shows experimental results on the relationship between the main injection preceding period Δθ defined as Δθ = θ _FB −θ _MB and the emission amount of harmful exhaust gas components under the condition of 〜0.2. In FIG. 5, HC is the total hydrocarbon concentration in the exhaust gas, a concentration of the NO _x nitrogen oxides in the exhaust gases, when not wearing the ignition injector subscripts S which was subjected to each invention the subscript W Means the case of adopting the means. HC _W / HC in FIG.
_s ≦ 1.0 and _NO XW / _{NO XS} ≦ 1.0 approximately satisfying region is at a good combustion situation in consideration of the prevention of exhaust pollution, appropriate for ignition spray injection start timing in this light (theta _FB) FIG. 6 shows the relationship between the main injection leading periods (Δθ). The above equation (1) expresses this appropriate Δθ by a simple linear equation.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment in which one ignition injection valve 2 is used in the present invention, and FIG. 2 shows a second embodiment in which four ignition injection valves having a large cylinder diameter are mounted. Each is shown. In FIG. 1, a piston 4 that slides in a vertical direction is inserted into a cylinder F, and a cylinder head B is attached to an upper end of the cylinder F. A main injection valve 1 having multiple injection ports is mounted at the center of the cylinder head B, and the injection port 1A slightly projects into the combustion chamber A from the lower surface of the cylinder head B. The ignition injection valve 2 is mounted at a position corresponding to the peripheral portion of the combustion chamber A and deeply depressed inward from the lower surface of the cylinder head B. The injection valve 2 of the cylinder head B to which the injection valve 2 is mounted
A trumpet-shaped spray guide hole C is formed from a portion corresponding to the injection port portion 2 </ b> A toward the combustion chamber A. A glow plug 3 is mounted in the spray guide hole C and at a position slightly deeper than the lower surface of the cylinder head B. I have.

The fuel injection pumps for supplying the low cetane number fuel to the main injection valve 1 and the ignition injection valve 2 are D and E, respectively, and any fuel injection timing can be selected. Since the main injection valve 1 is a multi-injection nozzle and starts the injection before the ignition injection valve 2, a large number of main spray patterns y corresponding to the number of injection holes are firstly provided in the combustion chamber in the example shown in FIG. Then, the flame of the ignited spray x forcibly ignited at the injection timing as shown in FIG. 4 is ejected from the spray guide hole C, igniting the main spray sufficiently diffused into the combustion chamber, and It becomes the whole combustion.

[0011]

According to the present invention, the main spray is at least 8 ° at the crank angle and at most 30 ° at the crank angle as compared with the spray for ignition.
Since there is a means to advance and advance the injection,
With diffusing main spray to the whole combustion chamber, improved air utilization rate, significantly reducing the emission of unburned hydrocarbon HC and nitrogen oxides NO _x as an exhaust gas purification measures, the combustion of for an additional combustion chamber throughout It is possible to provide a low cetane number fuel engine that can make the piston surface concentration relatively uniform and prevent the occurrence of trouble due to local concentration of heat load.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a low cetane number fuel engine according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a low cetane number fuel engine according to a second embodiment of the present invention.

FIG. 3 shows a fuel spray pattern according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of the injection timing of the main injection valve and the ignition injection valve of the present invention.

FIG. 5 is an explanatory diagram of an experimental result regarding exhaust gas purification of the present invention.

FIG. 6 is an explanatory diagram showing a region of an appropriate Δθ according to the present invention.

FIG. 7 is a configuration diagram of a conventional low cetane number fuel engine.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Main injection valve, 1A ... Injection part of main injection valve, 2 ... Ignition injection valve, 2A ... Injection part of ignition injection valve, 3 ... Glow plug, A ... Combustion chamber, B ... Cylinder head, C ... Spray Guide hole.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02P 13/00 303 F02P 13/00 303A 19/00 19/00 A

Claims (1)

(57) [Claims] In a direct injection type diesel engine using a low cetane number fuel and having a combustion chamber (A) recessed at the top of a piston, an injection port (from the lower surface of a cylinder head (B)) to the combustion chamber side. 1A) a main injection valve (1) having a multi-injection nozzle protruding slightly, and a spray guide hole (C) formed in a trumpet shape from the inside of the cylinder head toward the combustion chamber (A). An ignition injection valve (2) having an injection port (2A) located at the back of the spray guide hole, and a glow plug (3) arranged such that a heating section protrudes into the spray guide hole. The main injection valve (1) is pre-injected to the ignition injection valve (2), the angle of the pre-injection is Δθ, and the ignition spray injection start timing is θ _{FB. / 15 × θ FB + 8 °} ) ≦ Δθ ≦ (-10 / 15 × θ FB + 0 °) where _{-15 ° ≦ θ FB ≦ 0 °} ( negative is a jetting apparatus is set to be BTDC) low cetane number fuel engine.