CN113669156B

CN113669156B - Direct injection type dual-fuel engine using polymethoxy dimethyl ether prepared by methanol hydrolysis as ignition agent and control method thereof

Info

Publication number: CN113669156B
Application number: CN202110919364.XA
Authority: CN
Inventors: 丁宇; 马文举; 向拉; 贲虹凯; 李兆
Original assignee: Harbin Engineering University
Current assignee: Harbin Engineering University
Priority date: 2021-08-11
Filing date: 2021-08-11
Publication date: 2023-02-14
Anticipated expiration: 2041-08-11
Also published as: CN113669156A

Abstract

The invention aims to provide an in-cylinder direct injection type dual-fuel engine using polymethoxy dimethyl ether prepared by methanol hydrolysis as a combustion initiator and a control method thereof. The invention can fully utilize the waste gas energy of the dual-fuel engine under high load and improve the utilization rate of the energy.

Description

Direct injection type dual-fuel engine using polymethoxy dimethyl ether prepared by methanol hydrolysis as ignition agent and control method thereof

Technical Field

The invention relates to an engine and a control method thereof, in particular to a dual-fuel engine and a control method thereof.

Background

Natural gas is widely used in the engine industry because of its high calorific value, clean emission, and abundant reserves. Most of marine dual-fuel engines adopt Liquefied Natural Gas (LNG) as a main fuel, and the LNG is vaporized into gaseous natural gas to participate in combustion. The ignition temperature of natural gas under normal pressure is about 600-650 ℃, which is far higher than that of diesel oil (about 280 ℃), and the natural gas is difficult to ignite and burn directly in a compression ignition mode, so that an engine using the natural gas as a main fuel needs external conditions to assist ignition. At present, the marine dual-fuel engine mostly adopts an ignition type ignition mode using diesel oil as an ignition agent.

Polyoxymethylene dimethyl ether (PODON) is a general name of linear polyether substances, has a molecular structure with only two chemical bonds of C-O bond and C-H bond, has the characteristics of high cetane number, high oxygen content, good volatility, no sulfur and aromatic hydrocarbon and the like, and is considered to be the oxygen-containing fuel with the best application prospect. A large number of researches show that the oxygen-carrying in the oxygen-containing fuel molecules can obviously improve the local fuel-air equivalent ratio in the combustion process, can effectively reduce the generation of soot under the condition of not obviously changing the combustion characteristics, has obvious advantages in changing the two-law contradictory relation of NOx and soot, does not contain S element in polymethoxy dimethyl ether, and can realize the zero emission of SOx from the source.

When the dual-fuel engine works under low load, the turbine can fully utilize the energy of the exhaust gas discharged by the engine, but when the engine works under high load, the energy of the discharged exhaust gas is increased due to the increase of the displacement, so that the rotating speed of the turbine is increased, and meanwhile, the rotating speed of the compressor is synchronously increased, so that the supercharging pressure of the engine is directly overhigh, and the influence of engine knock, compressor surge and the like is generated.

Although the dual-fuel engine using diesel oil as an ignition agent can meet the requirement of reducing emission pollutants, the current marine dual-fuel engine only can meet the Tier II emission standard regulated by the International Maritime Organization (IMO), and is difficult to meet the Tier III emission standard to be implemented. In order to reduce pollutant emission as much as possible, the proportion of the ignition agent of the dual-fuel engine is extremely low, the combustion rate of natural gas cannot be obviously improved, and the problem of poor dynamic characteristics of the dual-fuel engine is caused, and the natural gas supply mode adopts a branch pipe natural gas injection mode, so that the volumetric efficiency loss is caused, and compared with a diesel engine of the same type, the output power is reduced by 20%. Therefore, how to reduce the pollutant discharge and avoid the output power reduction is always an urgent problem to be solved in the field.

Disclosure of Invention

The invention aims to provide an in-cylinder direct injection type dual-fuel engine which can fully utilize the energy of exhaust gas of the dual-fuel engine under high load and takes polyoxymethylene dimethyl ether prepared by hydrolysis of methanol as a detonator and a control method thereof.

The purpose of the invention is realized as follows:

the invention relates to an in-cylinder direct injection type dual-fuel engine using polymethoxy dimethyl ether as a combustion initiator prepared by methanol hydrolysis, which is characterized in that: the device comprises an NG storage tank, an LNG storage tank, an oxidation reactor, a solid bed condensation reactor, a refining reactor, a dehydrogenation tower, a PODEN storage tank and a methanol storage tank, wherein an immersed pump is arranged in the LNG storage tank and is connected with a cold flow end inlet of a vaporizer, vaporized natural gas flows into the NG storage tank from an outlet end of the vaporizer, a turbocharger compressor is connected with a gas inlet main pipe through an intercooler, the gas inlet main pipe is connected with a high-pressure common rail system, an exhaust main pipe is connected with a turbocharger turbine, a waste gas bypass valve is arranged between the exhaust main pipe and the turbocharger turbine and is connected with the oxidation reactor, the oxidation reactor is connected with the solid bed condensation reactor, the solid bed condensation reactor is respectively connected with the refining reactor and the atmosphere, the methanol storage tank is respectively connected with the oxidation reactor and the solid bed condensation reactor through a flow divider, the refining reactor is connected with the PODEN storage tank through the dehydrogenation tower, polymethoxy dimethyl ether in the PODEN storage tank and gaseous natural gas in the NG storage tank enter a cylinder through the high-pressure common rail system, and impurities are separated out from the upper end of the dehydrogenation tower and circulated to the oxidation reactor.

The direct injection type dual-fuel engine using polyoxymethylene dimethyl ether prepared by hydrolysis of methanol as a combustion initiator can further comprise:

1. the method comprises the following steps that external air is compressed through a turbocharger compressor, the cooled compressed air enters an air cylinder, after an air inlet stage is finished, vaporized natural gas enters the air cylinder through a high-pressure common rail system at the beginning of a compression stroke and the closing time of an air inlet valve and is mixed with air in the air cylinder, liquid polymethoxy dimethyl ether is sprayed into the air cylinder through the high-pressure common rail system at the top dead center of compression, the polymethoxy dimethyl ether is subjected to spontaneous combustion in a high-temperature and high-pressure environment, so that the mixed air in the air cylinder is ignited, a pressure sensor is arranged at the outlet end of the turbocharger compressor, and a temperature sensor is arranged inside an oxidation reactor and a solid bed condensation reactor.

The invention relates to a control method of a direct injection type dual-fuel engine using polymethoxy dimethyl ether prepared by methanol hydrolysis as a detonator, which is characterized by comprising the following steps: the opening of the waste gas bypass valve, the preparation of the PODEN and the PODEN fuel ratio are respectively controlled according to different engine loads:

when the working load of the engine is in a low-load working condition of 0-50 percent, the waste gas bypass valve is in a completely closed state, all high-temperature and high-pressure waste gas flowing out through an exhaust pipe of the engine enters the turbocharger to push the turbine to do work, and the ignition agent PODEN required by the engine is provided by a PODEN storage tank;

when the working load of the engine is 50-80%, the engine is in a medium-load working condition, when the working load of the engine is more than 50%, a waste gas bypass valve is opened, a part of high-temperature and high-pressure waste gas is bypassed to a formaldehyde oxidation reactor, the bypassed high-temperature and high-pressure waste gas forms a high-temperature normal-pressure reaction condition of 350 ℃ in the oxidation reduction reactor to provide energy for preparing PODEN by hydrolyzing methanol, the opening of the waste gas bypass valve is in positive correlation with the load of the engine, and under the working condition of 80%, the opening of the waste gas bypass valve is maximum, and the consumption of an ignition agent in each cycle is equal to the generation amount;

when the engine working load is in a high-load working condition (80-100%), keeping the highest supercharging pressure of the turbocharger, completely introducing all redundant waste gas into a polymethoxy dimethyl ether system to prepare PODEN, when the engine load is higher than 80%, keeping the proportion of the ignition agent consistent with the 80% working condition, storing the redundant PODEN in a PODEN storage tank for use under a low working condition, and when the PODEN storage tank is full, keeping the proportion of the ignition agent in positive correlation with the engine load, namely, the consumption of the ignition agent in each cycle is equal to the generation.

The invention has the advantages that:

1. the waste gas energy of the dual-fuel engine under high load can be fully utilized, and the energy utilization rate is improved.

2. The polyoxymethylene dimethyl ether prepared by hydrolysis of methanol is used as an ignition agent, is an oxygen-containing fuel, can improve the local fuel-air equivalent ratio in the combustion process, can effectively reduce the generation of soot under the condition of not remarkably changing the combustion characteristics, does not contain S element, and can realize the zero emission of SOx from the source. Moreover, the polyoxymethylene dimethyl ethers have high combustion speed, can obviously improve the combustion rate of natural gas, and realize the high-efficiency combustion of the natural gas.

3. The direct injection type fuel supply mode in the cylinder is adopted, natural gas is injected at the beginning of a compression stroke and the closing time of an air inlet valve, volumetric efficiency loss is avoided, the power of the dual-fuel engine can be almost consistent with that of a diesel engine with the same type, and the problems of methane escape and the like can be reduced.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a flow chart of the present invention.

Detailed Description

The invention will now be described in more detail by way of example with reference to the accompanying drawings in which:

referring to fig. 1-2, the dual fuel engine may be classified into an out-cylinder supply type and an in-cylinder supply type according to an intake mode. The cylinder gas supply type engine sprays natural gas after an air inlet valve is closed, fuel does not occupy air inlet volume, volume efficiency loss hardly exists, thermal efficiency of the cylinder gas supply type engine is close to that of a diesel engine of the same type, and methane escape and other problems hardly exist. However, the in-cylinder direct injection type dual-fuel engine has uneven gas mixture, and more ignition agent is needed to ignite natural gas in order to ensure the combustion quality, and the diesel combustion product is rich in SOx and particulate matters. The molecular formula of polyoxymethylene dimethyl ethers (PODEN) is CH3O- (CH 2O) n-CH3, and the polyoxymethylene dimethyl ethers are linear polyether substances with low molecular weight. The PODEN only contains C-O bonds and C-H bonds in a molecular structure, has the characteristics of high cetane number, high oxygen content, good volatility, no sulfur, no aromatic hydrocarbon and the like, and when the polymerization degree n = 3-5, the density, viscosity, melting point and other physicochemical properties of the PODEN are very close to those of diesel oil, so that the PODEN is an oxygen-containing fuel which can perfectly replace the diesel oil as a combustion initiator, the local fuel-air equivalent ratio in the combustion process is improved, the soot generation can be effectively reduced under the condition of not remarkably changing the combustion characteristic, and the polymethoxy dimethyl ether does not contain S element, so that the zero emission of SOx can be realized from the source. Moreover, the polyoxymethylene dimethyl ethers have high combustion speed, can obviously improve the combustion rate of natural gas, and realize the high-efficiency combustion of the natural gas.

The technical scheme adopted by the invention is as follows: methanol is used as an initial raw material to prepare oxygen-containing fuel polymethoxy dimethyl ether, PODEN is used as a detonator to ignite natural gas for combustion, and the combustion characteristic of the PODEN with a high combustion rate is used to accelerate the combustion rate of the natural gas, so that the dynamic characteristic of the dual-fuel engine is improved. The synthesis of PODEn requires two types of starting materials: the invention provides a terminal group (CH 3O-and CH 3-) and a methyleneoxy polymeric monomer (-CH 2O-), wherein methanol is adopted to provide the terminal group, formaldehyde aqueous solution is adopted to provide the methyleneoxy polymeric monomer, and the two raw materials generate PODEN under the catalysis of ion exchange resin.

The invention relates to an in-cylinder direct injection type dual-fuel engine using polymethoxy dimethyl ether prepared by methanol hydrolysis as a pilot agent and a control method thereof, which comprises an immersed pump 1, an LNG storage tank 2, an LNG stop valve 3, a vaporizer 4, an NG storage tank 5, an air inlet main pipe 6, an intercooler 7, a pressure sensor 8, a compressor 9, a turbine 10, a dehydrogenation tower 11, a refining reactor 12, a solid bed condensation reactor 13, a waste gas bypass valve 14, an oxidation reactor 15, a flow divider 16, a PODEN storage tank 17, a methanol storage tank 18, an exhaust main pipe 19, a cylinder 20, a high-pressure common rail system 21, a connecting pipeline and the like. An immersed pump 1 is arranged in an LNG storage tank 2, the immersed pump 1 is connected with a cold flow end inlet of a vaporizer 4 through a pipeline, vaporized natural gas flows into an NG storage tank 5 from an outlet end of the vaporizer, an inlet end of an intercooler 7 is connected with an outlet end of a turbocharger compressor 9, an outlet end of the intercooler 7 is connected with an air inlet manifold 6, a turbocharger turbine 10 is directly connected with an exhaust manifold 19, a waste gas bypass valve 14 is arranged between the exhaust manifold 19 and the turbocharger turbine 10 to bypass a part of high temperature and high pressure into an oxidation reactor 15 to form a 350 ℃ high temperature and normal pressure reaction condition, waste gas after acting continues to enter a solid bed condensation reactor 13 to form a reaction condition with the temperature of 120 ℃ and the pressure of 2.0MPa, and then the reaction condition is directly discharged into the atmosphere. The methanol storage tank 18 is respectively connected with the oxidation reactor 15 and the solid bed condensation reactor 13 through a flow divider 16, the outlet end of the solid bed condensation reactor 13 is connected with the refining reactor 12, the refined polymethoxy dimethyl ether mixture enters the dehydrogenation tower 11 for separation, impurities are separated from the upper end of the dehydrogenation tower 11 and circulate to the oxidation reactor 15, the polymethoxy dimethyl ether is separated from the lower end of the dehydrogenation tower 11 and enters the PODEN storage tank 17, and the polymethoxy dimethyl ether in the PODEN storage tank 17 and the gaseous natural gas in the NG storage tank 5 enter the cylinder 20 through the high-pressure common rail system 21 to participate in combustion.

When the dual-fuel engine works, outside air is firstly compressed by a turbocharger compressor 9 and then enters an intercooler 7 for cooling, the cooled compressed air enters an air cylinder 20, after the air inlet stage is finished, vaporized natural gas enters the air cylinder 20 through a high-pressure common rail system 21 at the moment when a compression stroke starts and an air inlet valve is closed, the natural gas is mixed with the air in the air cylinder, liquid polymethoxy dimethyl ether is sprayed into the air cylinder 20 through the high-pressure common rail system 21 at the moment of a compression top dead center, and the polymethoxy dimethyl ether spontaneously ignites in a high-temperature and high-pressure environment, so that the mixed gas in the air cylinder is ignited to do work. In order to meet the output power of the turbine and the internal temperature of the reactor, a pressure sensor 8 is arranged at the outlet end of a compressor 9 of the turbocharger, and temperature sensors are arranged inside an oxidation reactor 15 and a solid bed condensation reactor 13 and used for monitoring the internal temperature of the reactor. The opening degree of the waste gas bypass valve 14 is comprehensively adjusted through the pressure at the outlet end of the turbocharger compressor 9 and the internal temperature of the oxidation reactor 15 and the solid bed condensation reactor 13.

When the dual-fuel engine works under medium and high load, the energy of exhaust gas discharged by the engine is increased rapidly, so that the rotating speed of a turbine is increased, and the influences of engine knock, compressor surge and the like caused by overhigh supercharging pressure of the engine are avoided.

The system for preparing polymethoxy dimethyl ether by hydrolyzing methanol mainly comprises a formaldehyde production unit, a condensation reaction unit, a refining unit and a separation unit. In the invention, high-temperature waste gas which is led out through a waste gas bypass valve 14 firstly enters an oxidation reactor 15, high-temperature normal-pressure reaction conditions of 350 ℃ are formed in the oxidation reactor 14, methanol which flows out from a methanol storage tank 14 is evaporated in the oxidation reactor 15 and mixed with air, formaldehyde is generated under the action of an iron-molybdenum oxidation catalyst, the formaldehyde is mixed with water to obtain a concentrated formaldehyde aqueous solution, the formaldehyde aqueous solution is mixed with the methanol and enters a solid bed condensation reactor 13 to carry out condensation reaction, a terminal group is provided by the methanol, a methylene oxide group polymerization monomer is provided by the formaldehyde aqueous solution, a condensation reaction is carried out under the catalysis of ion exchange resin to generate a crude polymethoxy dimethyl ether product, main impurities comprise water, methyl formate, formic acid, unreacted formaldehyde and the like, the crude polymethoxy dimethyl ether product continuously enters a refining reactor, refined polymethoxy dimethyl ether is obtained under the catalysis of a catalyst, the refined polymethoxy dimethyl ether and residual impurities enter a dehydrogenation tower 11, a mixture of the methanol, the formaldehyde and the like is separated out at the top of the tower, the mixture circulates to the oxidation reactor 15 to continuously participate in an oxidation-reduction reaction, a polymethoxy dimethyl ether mixture of n > 2 is obtained at the bottom of the tower, an En dimethyl ether common rail is stored in a high-pressure compression system 17, and is stored on a piston system, and then passes through a piston, and is stored on a piston, and is finished piston, and is stored on a common rail, and a piston system, and is finished cylinder, and the common rail.

When the dual-fuel engine works, outside air is firstly compressed by a turbocharger compressor 9 and then enters an intercooler 7 for cooling, the cooled compressed air enters an air cylinder 20, after the air inlet stage is finished, vaporized natural gas enters the air cylinder 20 through a high-pressure common rail system 21 at the moment when a compression stroke starts and an air inlet valve is closed, the natural gas is mixed with the air in the air cylinder, liquid polymethoxy dimethyl ether is sprayed into the air cylinder 20 through the high-pressure common rail system 21 at the moment of a compression top dead center, and the polymethoxy dimethyl ether spontaneously ignites in a high-temperature and high-pressure environment, so that the mixed gas in the air cylinder is ignited to do work.

The outlet end of a turbocharger compressor 9 is provided with a pressure sensor 8, a waste gas bypass valve is arranged between the inlet end of an oxidation reactor 14 and an exhaust manifold, and temperature sensors are arranged inside the oxidation reactor 14 and a solid bed condensation reactor 13 and used for monitoring the temperature inside the reactors.

The invention relates to an in-cylinder direct injection type dual-fuel engine using polyoxymethylene dimethyl ether prepared by methanol hydrolysis as a combustion initiator and a control method thereof, wherein the opening of a waste gas bypass valve of the dual-fuel engine, the preparation of PODEN and the fuel proportion of the PODEN can be respectively controlled according to different engine loads, and the specific method comprises the following steps:

low load (0-50%): when the working load of the engine is between 0 and 50 percent, the working condition is called a low-load working condition. In order to prevent the turbocharger boost pressure from being too low, the engine output is greatly reduced. At the moment, the waste gas bypass valve is in a completely closed state, all high-temperature and high-pressure waste gas flowing out through an exhaust pipe of the engine enters the turbocharger to push the turbine to do work, the ignition agent PODEN required by the engine is provided by the PODEN storage tank, and the PODEN cannot be actively prepared under the working condition, so that the proportion of the ignition agent is extremely small (about 0.2%), and at the moment, the PODEN mainly plays a role in ignition.

Medium load (50% -80%): when the working load of the engine is 50% -80%, the engine is called as a medium-load working condition. When the working load of the engine is more than 50%, a waste gas bypass valve is opened, a part of high-temperature and high-pressure waste gas is bypassed to a formaldehyde oxidation reactor, the bypassed high-temperature and high-pressure waste gas forms a 350 ℃ high-temperature and normal-pressure reaction condition in the oxidation reduction reactor, energy is provided for preparing PODEN through methanol hydrolysis, the opening of the waste gas bypass valve is in positive correlation with the load of the engine, and the opening of the waste gas bypass valve is the largest under 80% of working conditions. Similarly, the proportion of the ignition agent is in positive correlation with the engine load, and in order to utilize the characteristic of high PODEN combustion rate, the combustion rate of natural gas is accelerated, the combustion process of the engine is improved, and the consumption amount of the ignition agent per cycle is equal to the generation amount.

High load (80-100%): when the working load of the engine is 80% -100%, the engine is called as a high-load working condition. Under the high-load working condition, under the condition that the highest supercharging pressure of a turbocharger is kept, all redundant exhaust gas is led into a polymethoxy dimethyl ether system to prepare PODEN, when the engine load is higher than 80%, the proportion of the ignition agent is kept consistent with the 80% working condition, at the moment, the preparation amount of the PODEN is larger than the consumption amount, the redundant PODEN is stored in a PODEN storage tank to be used under the low working condition, after the PODEN storage tank is filled, the proportion of the ignition agent is kept in positive correlation with the engine load, namely, the consumption amount of the ignition agent per cycle is equal to the generation amount.

Claims

1. An in-cylinder direct injection type dual-fuel engine using polyoxymethylene dimethyl ether prepared by methanol hydrolysis as a detonator is characterized in that: the device comprises an NG storage tank, an LNG storage tank, an oxidation reactor, a solid bed condensation reactor, a refining reactor, a dehydrogenation tower, a PODEN storage tank and a methanol storage tank, wherein an immersed pump is arranged in the LNG storage tank and is connected with a cold flow end inlet of a vaporizer, vaporized natural gas flows into the NG storage tank from an outlet end of the vaporizer, a turbocharger compressor is connected with a gas inlet main pipe through an intercooler, the gas inlet main pipe is connected with a high-pressure common rail system, a gas outlet main pipe is connected with a turbocharger turbine, a waste gas bypass valve is arranged between the gas outlet main pipe and the turbocharger turbine and connected with the oxidation reactor, the oxidation reactor is connected with the solid bed condensation reactor, the solid bed condensation reactor is respectively connected with the refining reactor and the atmosphere, the methanol storage tank is respectively connected with the oxidation reactor and the solid bed condensation reactor through a flow divider, the refining reactor is connected with the PODEN storage tank through the dehydrogenation tower, polymethoxy dimethyl ether in the PODEM storage tank and gaseous natural gas in the NG storage tank enter a cylinder through the high-pressure common rail system, and impurities are separated from the upper end of the dehydrogenation tower and circulated to the oxidation reactor.

2. The in-cylinder direct injection type dual-fuel engine for preparing polyoxymethylene dimethyl ethers as ignition agents through methanol hydrolysis as claimed in claim 1, wherein: the method comprises the steps that external air is compressed through a turbocharger compressor, the cooled compressed air enters a cylinder, after the air inlet stage is finished, vaporized natural gas enters the cylinder through a high-pressure common rail system at the moment when a compression stroke starts and an air inlet valve is closed and is mixed with air in the cylinder, liquid polymethoxy dimethyl ether is sprayed into the cylinder through the high-pressure common rail system at the moment of a compression top dead center, the polymethoxy dimethyl ether is subjected to spontaneous combustion in a high-temperature high-pressure environment to ignite mixed air in the cylinder, a pressure sensor is arranged at the outlet end of the turbocharger compressor, and temperature sensors are arranged inside an oxidation reactor and a solid bed condensation reactor.

3. A control method of a direct injection type dual-fuel engine which is suitable for preparing polyoxymethylene dimethyl ethers as ignition agents through methanol hydrolysis according to claim 1 or 2 is characterized in that: the opening of the waste gas bypass valve, the preparation of the PODEN and the PODEN fuel ratio are respectively controlled according to different engine loads:

when the working load of the engine is 50-80%, the engine is in a medium-load working condition, when the working load of the engine is more than 50%, a waste gas bypass valve is opened, a part of high-temperature and high-pressure waste gas is bypassed to a formaldehyde oxidation reactor, the bypassed high-temperature and high-pressure waste gas forms a high-temperature normal-pressure reaction condition of 350 ℃ in the oxidation reduction reactor, energy is provided for preparing PODEN through methanol hydrolysis, the opening of the waste gas bypass valve is positively correlated with the load of the engine, under the 80% working condition, the opening of the waste gas bypass valve is the largest, and the consumption and the generation amount of a combustion agent in each cycle are equal;

when the engine working load is in a high-load working condition (80-100%), keeping the highest supercharging pressure of the turbocharger, completely introducing redundant exhaust gas into a polymethoxy dimethyl ether system to prepare PODEN, when the engine load is higher than 80%, continuously keeping the proportion of the ignition agent consistent with the 80% working condition, wherein the preparation amount of the PODEN is larger than the consumption amount, storing the redundant PODEN in a PODEN storage tank so as to be used under the low working condition, and after the PODEN storage tank is filled, continuously forming a positive correlation relationship between the proportion of the ignition agent and the engine load, namely the consumption amount of the ignition agent per cycle is equal to the generation amount.