CN109268170B - Compound air supply dual fuel engine system with dual needle valve injector and combustion method - Google Patents

Abstract

The invention discloses a compound air supply dual-fuel engine system with double-needle valve fuel injector and a combustion method, which belong to the field of dual-fuel engine combustion methods. The system includes intake port, intake valve, exhaust port, exhaust valve, manifold low-pressure injection natural gas injection valve, high-pressure in-cylinder direct injection natural gas injection valve, dual-needle valve injector and omega-shaped combustion chamber. When the engine is running at low load and medium load, the high-pressure in-cylinder direct injection natural gas injection valve is controlled to inject gas into the cylinder one or more times; Different fuel and gas injection control strategies are used under different engine operating conditions. By controlling the natural gas injection quantity, injection times and injection timing of the manifold low-pressure injection natural gas injection valve and the high-pressure in-cylinder direct injection natural gas injection valve, the engine can achieve high-efficiency and low-emission combustion in the full range of operating conditions, which can improve in-cylinder combustion and widen the engine load range. Effectively reduce NOx emissions.

Description

Compound air supply dual fuel engine system with dual needle valve injector and combustion method

technical field

The invention belongs to the field of dual-fuel engine combustion methods, and in particular relates to a dual-needle valve fuel injector compound air-supply dual-fuel engine system and a combustion method.

Background technique

With the shortage of fossil energy and increasingly strict emission regulations, natural gas has developed into a promising alternative fuel for diesel due to its high combustion efficiency, cleanliness and environmental protection, and good anti-knock performance. Compared with the spark ignition natural gas engine, the diesel pilot natural gas dual-fuel engine has better power performance, and the emission performance can meet the requirements of international emission regulations.

The dual-fuel engine is modified from a diesel engine, and the study of the combustion model of the dual-fuel engine is inseparable from the foundation of the traditional engine combustion model. After mixing natural gas, the heat release law changes, so the combustion model of the dual-fuel engine is different from the traditional combustion model. Spatially, the traditional combustion models of compression ignition engines can be divided into zero-dimensional models, quasi-dimensional models and multi-dimensional models. Both the zero-dimensional model and the quasi-dimensional model analyze the combustion process based on thermodynamic principles. The zero-dimensional model treats the entire cylinder as a uniform field and does not consider the variation of parameters with spatial position. The quasi-dimensional model treats the space as partitions, and the parameters between the regions are different from each other, which can predict the main performance parameters and emissions of the combustion process to a certain extent. These two types of models are simple in method and low in computational cost, and are currently widely used in engineering. The multi-dimensional model obtains information such as the transient spatial distribution of gas velocity, temperature, pressure and component concentration by solving basic partial differential equations such as mass conservation, momentum conservation, energy conservation and equation of state. But solving the partial differential equation will make the numerical calculation complicated and the computational cost is high. With the development of numerical simulation technology and computer technology, the coupling of multi-dimensional model and chemical kinetic model has become an important means to establish combustion model.

Yan Zhaoda et al. established a thermodynamic-chemical reaction kinetic mathematical model for the combustion process of a dual-fuel engine. The model uses 14 chemical components and 32 elementary reactions to simulate the combustion process of a uniform air/methane mixture in the cylinder. The constant volume combustion model and heat release model of pilot oil are proposed. The two models are coupled to establish a mathematical model of chemical reaction kinetics of the combustion process of diesel and natural gas dual-fuel engines. This model can give the temperature and pressure of various components in the cylinder. , concentration and heat release rate, and can reflect the influence of pilot fuel equivalence ratio, fuel injection timing, and intake air temperature on the combustion process. Zhao Luowei established a dual-fuel engine combustion model based on chemical kinetics, including pilot fuel spray model, ignition delay model, emission model, turbulent combustion flame propagation analysis model and methane containing 38 components and 113 elementary reactions By simplifying the dynamic model, the combustion model can be better used to predict the combustion heat release law, emission characteristics and in-cylinder pressure variation of dual-fuel engines. Song Jinou et al. used KIVI-3V software to study the effect of swirl ratio on the combustion rate of diesel-piloted natural gas engines. Pirouzpanah et al. established a pilot oil spray model, a multi-zone model of natural gas flame propagation, and an emission model of HC, CO, NO, and soot. Mousavi et al. used KIVI software to establish a diesel-ignition natural gas dual-fuel kinetic model to simulate the process of fuel spray atomization, combustion and pollutant emission. Jie Liu et al. used KIVA-3V to simulate the in-cylinder combustion of a dual-fuel engine, and studied the effect of engine speed on the combustion process of the dual-fuel engine and the effect on the in-cylinder temperature and the spatial distribution of pollutants. The dual-fuel combustion mechanism model based on chemical kinetics has great advantages in predicting the combustion process and emissions, and has gradually become a research hotspot.

At present, the natural gas supply methods of diesel-piloted natural gas dual-fuel engines mainly adopt two types of out-cylinder gas supply and in-cylinder direct injection. The out-of-cylinder gas supply method is to install a natural gas injection valve in the intake manifold, and control the natural gas injection valve through the electronic control unit ECU to perform multi-point sequential injection. This gas supply method can control the gas injection amount of each cylinder, but the intake air is used. Channel injection of natural gas reduces charging efficiency and reduces engine output. During the scavenging process, a portion of the unburned mixture is exhausted, which affects the fuel economy of the engine. And when the engine is under low load, there are problems of low thermal efficiency and high HC emissions. The direct injection natural gas supply method in the cylinder is to inject the natural gas directly into the cylinder at a certain pressure when the compression stroke piston moves to the vicinity of the top dead center. loss, and at the same time, a more precise gas injection amount can be achieved. However, the mixing degree of direct injection natural gas and air in the cylinder is low, which makes the concentration of the mixture in the cylinder uneven and affects the combustion process in the cylinder.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a dual-needle valve injector compound air-supply dual-fuel engine system and combustion method to realize fast and flexible switching between engine gas mode and diesel mode, improve fuel power, economy and emission.

The object of the present invention is achieved through the following technical solutions:

The compound air supply dual fuel engine system with dual needle valve injector includes intake port, intake valve, exhaust port, exhaust valve, manifold low pressure injection natural gas injection valve, high pressure in-cylinder direct injection natural gas injection valve, Twin needle valve injectors and omega combustion chambers.

The low-pressure injection natural gas injection valve of the manifold is installed on the intake manifold, and the central axis of the low-pressure injection natural gas injection valve of the manifold is perpendicular to the central axis of the cylinder, which can speed up the intake process and is conducive to the formation of an intake vortex.

The high-pressure in-cylinder direct-injection natural gas injection valve is arranged obliquely on the cylinder head, and the high-pressure in-cylinder direct-injection natural gas injection valve has high gas injection precision and injects natural gas into the cylinder at high pressure.

The dual-needle valve injector is arranged on the cylinder head. The dual-needle valve injector is composed of two independent electronically controlled injectors with different flow rates. Each electronically controlled injector has an independent needle valve. , spring, solenoid valve, oil supply channel and multi-hole nozzle, that is, two independent solenoid valves in the valve body control the two needle valves to open and close independently.

Further, the dual-needle valve injector has two independent oil inlet passages, one oil inlet passage provides light diesel oil to the small-flow injector, and the other provides heavy oil to the large-flow injector. The light diesel oil has less impurities and ensures the injection accuracy of the small flow injector.

Further, the dual-needle valve fuel injector has two multi-hole nozzles, the nozzle part of the large-flow fuel injector has 8-12 nozzle holes; the nozzle part of the small-flow fuel injector has 4-6 nozzle holes. Under the same injection pulse width, the fuel injection flow rate of the small-flow injector is about 1% of the fuel injection flow of the large-flow injector, which realizes the precise control of the small flow rate of igniting diesel in the gas mode.

The combustion method of a compound air-supplied dual-fuel engine with dual-needle valve injector is as follows:

The engine operates in pure diesel mode at start and idle conditions, and can be switched to gas mode when the engine is running at low and medium loads. During the engine intake stroke, air enters the cylinder through the intake port. In the range from the closing of the intake valve to the top dead center of compression, the direct injection natural gas injection valve in the high-pressure cylinder is controlled to inject an appropriate amount of natural gas into the cylinder one or more times. The specific injection amount, injection timing and injection pulse width are determined by the actual engine The condition is fed back to the electronic control unit to control and adjust, so that a richer mixture is formed around the injector. Natural gas and air first form a mixture in the cylinder. Before the compression stroke is close to the top dead center, the dual-needle valve injector is controlled to inject a small amount of diesel pilot pre-mixed gas into the cylinder to realize the natural gas pre-mixed trace diesel pilot combustion. When the engine is running at high load, in the engine intake stroke stage, the low-pressure injection natural gas injection valve of the manifold is controlled to inject an appropriate amount of natural gas into the intake manifold, and the natural gas and air are mixed in the cylinder to form a relatively uniform mixture. Before the intake valve is closed to the compression top dead center, the high-pressure in-cylinder direct injection natural gas injection valve is controlled to inject two-stage gas into the cylinder. When approaching the top dead center of compression, the time interval between two gas injections is greater than 10°C A. The number of gas injections in the first stage is single or multiple. By controlling the timing of each gas injection and the ratio of the gas injection amount between the high-pressure in-cylinder direct injection natural gas injection valve and the manifold low-pressure injection natural gas injection valve, the gas injection in the cylinder can be controlled. A weakly stratified gas mixture is formed. The number of times of the second stage gas injection is single, so that a richer mixture is formed around the injector. The mixture is ignited with self-igniting diesel fuel and the stratified mixture in the cylinder is ignited. When the engine is converted from gas mode to diesel mode, the dual-needle valve injector can be controlled first to continue to inject pilot diesel, and when the compression is close to the top dead center, the dual-needle valve injector can be controlled to inject main fuel, main fuel and pilot diesel. Simultaneous injection ensures that both needle valves and nozzles are cooled by diesel oil and the thermal stress is balanced.

The beneficial effects of the present invention are:

According to the actual working conditions of the engine or when the gas mode fails, the two needle valves of the dual-needle valve injector can be controlled to work, so as to realize the fast and flexible switching between the engine gas mode and the diesel mode; in the gas mode, according to the different working conditions of the engine. It can adapt to different engine loads by controlling the natural gas injection quantity ratio and injection timing of the manifold low-pressure injection natural gas injection valve and the high-pressure in-cylinder direct injection natural gas injection valve; Theoretical gas mixture concentration around the ignition source improves fuel power, economy and emissions.

Description of drawings

Fig. 1 is the schematic diagram of the combustion system of the present invention;

Figure 2 is a partial schematic diagram of a dual-needle valve injector nozzle.

The corresponding relationship between the labels is: intake port 1, intake valve 2, exhaust port 3, exhaust valve 4, manifold low-pressure injection natural gas injection valve 5, high-pressure in-cylinder direct injection natural gas injection valve 6, double needle valve injection valve Fuel injector 7, ω-shaped combustion chamber 8, large flow injector needle valve body 9, small flow injector needle valve body 10.

Detailed ways

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings:

As shown in Figure 1 and Figure 2, the dual-needle valve fuel injector compound air supply dual-fuel engine system includes intake port 1, intake valve 2, exhaust port 3, exhaust valve 4, and manifold low pressure injection. Natural gas injection valve 5 , high pressure in-cylinder direct injection natural gas injection valve 6 , double needle valve injector 7 and ω-shaped combustion chamber 8 . The manifold low-pressure injection natural gas injection valve 5 is installed on the intake manifold, and the central axis of the manifold low-pressure injection natural gas injection valve 5 is perpendicular to the cylinder central axis, which can speed up the intake process and is conducive to the formation of an intake vortex. The high-pressure in-cylinder direct injection natural gas injection valve 6 is obliquely arranged on the cylinder head, and is used for multiple injections of gas into the cylinder. The angle between the center axis of the high-pressure cylinder direct injection natural gas injection valve 6 and the cylinder center axis is 40°-50°, and there is a certain installation distance between the high-pressure cylinder direct injection natural gas injection valve 6 and the double-needle valve injector 7, so that The natural gas injected by the high-pressure in-cylinder direct injection natural gas injection valve 6 is distributed near the central axis of the cylinder and near the nozzle of the double-needle valve injector 7 . The central axis of the double needle valve injector 7 is collinear with the central axis of the cylinder. The dual-needle valve injector 7 has an integrated structure composed of two injectors with different flow rates, and each injector has an independent needle valve, a spring, a solenoid valve, an oil supply channel and a multi-hole nozzle. The diameter of the two needle valves and the hole diameter of the multi-hole nozzle are different, and the needle valve and the multi-hole nozzle of the smaller diameter correspond to the small flow injector. In the case of the same injection pulse width, the injection flow of the small-flow injector is within 1% of the injection flow of the large-flow injector. An omega-shaped combustion chamber 8 is provided at the central position of the top surface of the piston. Among them, the manifold low pressure injection natural gas injection valve, the high pressure in-cylinder direct injection natural gas injection valve and the double needle valve fuel injector are connected with the engine electronic control unit and controlled by the electronic control unit.

The combustion method of a compound air-supplied dual-fuel engine with dual-needle valve injector is as follows:

The engine operates in pure diesel mode at start-up and idle conditions, and can be switched to gas mode when the engine is running at low and medium loads. In the gas mode, the manifold low-pressure injection natural gas injection valve 5 does not work, the high-pressure in-cylinder direct injection natural gas injection valve 6 works, and the engine adopts the in-cylinder direct injection natural gas supply mode. During the intake stroke of the engine, air enters the cylinder through the intake port. Before the intake valve 2 is closed to the compression top dead center, the high-pressure in-cylinder direct injection natural gas injection valve 6 is controlled to inject an appropriate amount of natural gas into the cylinder. The specific injection amount, injection timing and injection pulse width are fed back to the electronic control unit by the actual working conditions of the engine. Control adjustment. Natural gas and air first form a mixture in the cylinder. Within the range of 10-30°C A before the top dead center of the compression stroke, the dual-needle valve injector 7 is controlled to inject a small amount of diesel pilot premixed gas into the cylinder to achieve natural gas premixed with trace diesel pilot combustion.

When the engine is running at high load, the manifold low-pressure injection natural gas injection valve 5 and the high-pressure in-cylinder direct injection natural gas injection valve 6 both work, and the engine adopts the natural gas inlet port low-pressure injection combined with the in-cylinder direct injection natural gas supply mode; In the stroke stage, before the intake valve is closed, the low-pressure injection natural gas injection valve 5 of the manifold is controlled to inject an appropriate amount of natural gas; before the intake valve is closed to the compression top dead center, the high-pressure in-cylinder direct injection natural gas injection valve 6 is controlled. The natural gas is directly injected into the cylinder at high pressure, and the injection method is two-stage multiple injection. The high-pressure in-cylinder direct injection natural gas injection valve 6 performs the first-stage injection before the intake valve is closed to the compression top dead center, and the injection times are single or multiple times. When the second-stage injection time is close to the compression top dead center, the injection times for a single time. The time interval between two stages of natural gas injection is greater than 10°C A, and the specific injection amount, injection timing and injection pulse width are fed back to the electronic control unit for control and adjustment by the actual working conditions of the engine. Due to the different injection methods and timings of natural gas, the in-cylinder mixture forms different levels of concentration stratification and spatial distribution. The last direct injection of natural gas in the cylinder can form a richer mixture near the injector, while the natural gas and air mixture injected by the intake port, due to the early injection time, has sufficient mixing time to form a homogeneous mixture . In addition, when the in-cylinder air-fuel mixture is in a state of concentration stratification, the homogeneous air-fuel mixture has been deposited in the lowermost layer, which is beneficial to increase the flame propagation speed in the rapid combustion stage, and is beneficial to the propagation of the in-cylinder flame. At the time of pilot fuel injection, the high-temperature fuel ignites the surrounding rich mixture, and the ignition is stable and reliable. The stratified mixture in the cylinder is ignited with self-igniting diesel. Under this working condition, the gas injection quantity ratio and injection timing of the high-pressure in-cylinder direct injection natural gas injection valve 6 and the manifold low-pressure injection natural gas injection valve 5 are controlled to adapt to the engine load change and improve the combustion process.

When the engine gas mode fails or the natural gas reserves are insufficient, the engine is switched from the gas mode to the diesel mode, and the manifold low pressure injection natural gas injection valve 5 and the high pressure in-cylinder direct injection natural gas injection valve 6 do not work. The dual-needle valve injector 7 small-flow injector can be controlled to work first, and a small amount of diesel oil can be injected into the cylinder. When the compression stroke is close to the top dead center, the dual-needle valve injector 7 large-flow injectors are controlled to work, and the main fuel is injected into the cylinder. Double needle valve injector 7 large flow and small flow injectors work at the same time to ensure that both needle valves and nozzles are cooled by diesel oil to achieve thermal stress balance. At the same time, the main fuel and pilot diesel are injected at the same time, and the fuel beams influence each other, which is beneficial to the atomization and mixing of the fuel.

As mentioned above, in the engine gas mode, the stratified combustion in the mixed cylinder can be realized and the load range can be widened by controlling the gas injection quantity ratio and injection timing of the manifold low-pressure injection natural gas injection valve and the high-pressure in-cylinder direct injection natural gas injection valve. The use of high-pressure in-cylinder direct injection natural gas injection valve can realize more precise control of gas injection quantity and injection timing, and realize the gradient distribution of mixture gas concentration in the cylinder. A lean and homogeneous mixture is formed inside, which can effectively reduce _NOx emissions and optimize the combustion process.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (5)

1. Take double needle valve sprayer combined type gas feed dual fuel engine system, including intake duct (1), (2) intake valve, exhaust passage (3), exhaust valve (4), manifold low pressure injection natural gas injection valve (5), direct injection natural gas injection valve (6) in the high-pressure cylinder, double needle valve sprayer (7), omega shape combustion chamber (8), large-traffic sprayer needle valve body (9), small flow sprayer needle valve body (10), its characterized in that: the manifold low-pressure natural gas injection valve (5) is arranged on an intake manifold, the central axis of the manifold low-pressure natural gas injection valve (5) is vertical to the central axis of a cylinder, the direct-injection natural gas injection valve (6) in the high-pressure cylinder is obliquely arranged on a cylinder cover, the included angle between the central axis of the direct-injection natural gas injection valve (6) in the high-pressure cylinder and the central axis of the cylinder is 40-50 degrees, a gap is reserved between the direct-injection natural gas injection valve (6) in the high-pressure cylinder and a double-needle valve oil injector (7), natural gas injected by the direct-injection natural gas injection valve (6) in the high-pressure cylinder is distributed on the central axis of the cylinder, the central axis of the double-needle valve oil injector (7) is collinear with the central axis of the cylinder, the double-needle valve oil injector (7) has, the omega-shaped combustion chamber (8) is positioned in the center of the top surface of the piston.

2. The compound gas-fed dual fuel engine system with a dual needle valve injector of claim 1, wherein: the double needle valve oil injector is provided with two independent oil inlet channels, wherein one oil inlet channel provides light diesel oil for the small-flow oil injector, and the other oil inlet channel provides heavy oil for the large-flow oil injector.

3. The compound gas-fed dual-fuel engine system with the dual needle valve fuel injector of claim 1, characterized in that: the double-needle valve oil injector is provided with two multi-hole nozzles, and the nozzle part of the large-flow oil injector is provided with 8-12 jet holes; the nozzle part of the small-flow oil sprayer is provided with 4-6 spray holes, and the fuel injection flow of the small-flow oil sprayer is within 1% of the fuel injection flow of the large-flow oil sprayer under the condition of the same injection pulse width.

4. The combustion method of the combined type gas supply dual-fuel engine with the double-needle valve oil sprayer is characterized by comprising the following steps of:

(1) the engine adopts a pure diesel mode when starting and running under an idling working condition, is switched to a gas mode when running under low load and medium load, and controls a direct injection natural gas injection valve in a high-pressure cylinder to perform single or multiple natural gas injection to the cylinder in a range from an inlet valve to the front of a compression top dead center;

(2) when the engine runs at a high load, in the stage of an intake stroke of the engine, controlling a manifold low-pressure injection natural gas injection valve to inject a proper amount of natural gas to an intake manifold, and controlling a high-pressure in-cylinder direct injection natural gas injection valve to perform two-stage gas injection to the cylinder before an intake valve is closed to a compression top dead center, wherein the first-stage gas injection is performed when the intake valve is closed to a compression front half stage, and the second-stage gas injection is performed when the intake valve is close to the compression top dead center;

(3) when the engine is switched from a gas mode to a diesel mode, firstly, the double-needle valve oil injector is controlled to continuously inject pilot diesel oil, when the compression is close to a top dead center, the double-needle valve oil injector is controlled to inject main fuel oil, and the main fuel oil and the pilot diesel oil are simultaneously injected.

5. The combustion method of the compound gas supply dual-fuel engine with the double-needle valve oil injector as claimed in claim 4, is characterized in that: the first-stage fuel gas injection frequency is single or multiple, and the fuel gas injection quantity ratio of a direct injection natural gas injection valve and a manifold low-pressure injection natural gas injection valve in each time is controlled; and the second stage fuel gas injection frequency is single, so that a relatively thick mixed gas is formed around the fuel injector, a small amount of diesel oil injected by the double-needle valve fuel injector ignites the relatively thick mixed gas around the fuel injector after compression ignition at the fuel ignition injection time, and the self-ignited diesel oil is used for igniting the mixed gas with layered concentration in the cylinder.

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