HK1179319A - Method and system for operating a pressure ignition engine - Google Patents

Description

Method and system for operating a compression ignition engine

The present invention relates to a method of operating a compression ignition engine and in particular to operating said engine using ether containing fuel.

The invention also provides a system for applying the invention.

The most typical example of a compression ignition engine is a diesel engine that operates on high cetane diesel fuel. In order to reduce the environmental pollution caused by the combustion of diesel fuel, several attempts have been made in the past to replace diesel fuel with alternative fuels having a small environmental impact.

Ethers, particularly ethers prepared by dehydration of lower alcohols, such as dimethyl ether and diethyl ether, have proven to be superior diesel fuels.

The use of lower ethers as diesel fuel has been described in a number of publications, such as U.S. Pat. nos. 4,892,561, 5,906,664 and 7,449,034.

Although ether-based fuels have high efficiency and clean combustion characteristics in diesel engines, their main drawback is the difficulty of on-board storage and handling. At ambient conditions, dimethyl ether is in gaseous form. To convert dimethyl ether fuel to a more convenient liquid form, the fuel must be stored and handled under pressure.

Although diethyl ether is in liquid form at ambient conditions, this ether has a high vapor pressure and presents a high risk of explosion upon contact with air.

Modern diesel engines are provided with common rail fuel systems. The system consists of a high pressure pump and a fuel accumulator chamber (accumulation chamber) that stores fuel at high pressures greater than 2,000 bar. The accumulator chamber provides high pressure fuel to a plurality of fuel injectors. Excess fuel is withdrawn from the chamber, depressurized and recirculated to the fuel tank.

Such a system using ether as a fuel for a diesel engine is described in U.S. Pat. No. 6,340,003. By the method of this patent, the primary methanol fuel is pressurized and converted to ether-containing diesel fuel prior to being introduced into the accumulator chamber. The disadvantage of this method arises when the excess ether-containing fuel must be removed from the chamber and recycled to the fuel tank, which requires two tanks, one for the alcohol fuel and one for the converted ether-containing fuel.

It is a general object of the present invention to provide a method for converting a primary fuel based on a lower alcohol or a mixture of lower alcohols on board a vehicle into an ether containing secondary fuel for operating a compression ignition engine equipped with a common rail fuel system without the difficulties of handling and storing the secondary fuel, in particular in the vehicle.

In accordance with the above purpose, the present invention is a method for operating a compression ignition engine using an ether containing fuel obtained by converting a primary fuel based on an alcohol, comprising the steps of:

(a) continuously withdrawing the alcohol-based primary fuel from the fuel tank and pressurizing it to a final engine injection pressure in liquid form of the alcohol-based primary fuel;

(b) continuously introducing the pressurized alcohol-based primary fuel into a fuel accumulator chamber;

(c) continuously distributing the pressurized alcohol-based primary fuel into a tube connecting the accumulator chamber with an engine fuel injector;

(d) continuously converting the pressurized alcohol-based primary fuel into an ether-containing fuel prior to the fuel injector by contact with an alcohol dehydration catalyst disposed in each tube upstream of the fuel injector;

(e) continuously injecting the ether containing fuel into the engine at injection pressure; and

(f) continuously withdrawing a portion of the introduced alcohol-based primary fuel from the accumulator chamber; and

(g) depressurizing and recycling the withdrawn primary alcohol-based fuel to the fuel tank.

The present invention also provides a system for the above method, comprising:

a compression ignition engine;

a fuel tank adapted to store an alcohol-based primary fuel;

a high pressure pump for pressurizing the alcohol-based primary fuel;

an accumulator chamber adapted to receive and store the pressurized alcohol-based primary fuel;

a connecting pipe for connecting the accumulator chamber with a fuel injector for injecting fuel into the compression ignition engine;

an alcohol dehydration catalyst disposed within each of the connecting tubes between the accumulator chamber and the fuel injector; and

a recirculation line for recirculating excess alcohol-based primary fuel from the accumulator chamber to the fuel tank.

An advantage of the method and system of the present invention is that all of the ether fuel formed is immediately available for combustion in the engine and storage of excess ether fuel is avoided. The excess primary alcohol-based fuel is recycled to the fuel tank.

The formation of the ether fuel is achieved by the catalytic dehydration of the alcohol to its corresponding ether according to the following reaction:

2C_nH_{( 2n+2)}O ↔ C_2nH_(4n+2) + H₂O

the dehydration of alcohols to ethers is catalyzed by liquid or solid acids, such as sulfuric acid, alumina, silica alumina, zeolites, sulfonic acids, zirconium dioxide-tungstate, aluminum oxide phosphate.

Alcohol dehydration is an equilibrium reaction. Thus, equilibrium limitations prevent 100% conversion of alcohols to ethers and water.

At the reaction temperature of the ethanol-based primary fuel, for example consisting of 95w% ethanol and 5w% water, the equilibrium composition is 9-21w% ethanol, 19-22w% H at a dehydration temperature between 150 ℃ and 350 ℃₂O and 59-71w% diethyl ether. To ensure that the composition remains homogeneous, it is advantageous either as an additive when the primary fuel is supplied to the accumulator chamber, or as an additive in the fuel tank or when the primary fuel is supplied to the vehicleThe additive of the primary fuel is added to an emulsifier which is not substantially converted by the dehydration catalyst.

Suitable alcohols on which the primary fuel in the present invention can be based are, in addition to methanol and ethanol, also mixtures thereof and other alcohols.

The preferred alcohol mixture is a mixture of methanol and ethanol.

Other suitable primary alcohol-based fuels include methanol and blends of alcohols with hydrocarbons such as gasoline. The latter includes commercially available E85 (which typically comprises 85% ethanol, 13% gasoline, and 2% MTBE (methyl tertiary butyl ether)), other compositions of alcohol, gasoline, and gasoline additives may also be used in the present invention. Although they are referred to as mixtures of alcohols and hydrocarbons, gasoline and gasoline additives may contain small amounts of non-hydrocarbon materials, such as organometallic combustion catalysts. The primary fuel may also include water, provided that the primary fuel is miscible with water or an emulsifier is present so that water can be uniformly distributed in the primary fuel.

For purposes of this disclosure, secondary fuel shall be defined as a fuel mixture formed from a primary fuel as defined above. The secondary fuel contains ether and has useful ignition and combustion characteristics suitable for use in a compression ignition engine. The secondary fuel comprises the diethyl ether/ethanol/water mixture described above as well as a dimethyl ether/methanol/water mixture with a methanol content of up to 20% and a water content of up to 20%, and similar mixtures additionally comprising hydrocarbons, such as gasoline. In U.S. Pat. No. 7,449,034, diesel fuel containing dimethyl ether, methanol and up to 48% water has proven to be an effective fuel for compression ignition engines. When the primary fuel comprises gasoline (including additives), the gasoline will also be included in the secondary fuel because no significant gasoline conversion will occur over the dehydration catalyst.

Within the above range for the secondary fuel composition, the operating conditions of the process of the invention will generally be adjusted to an injection temperature of from 150 ℃ to 350 ℃ and an injection pressure of from 200 to 2,400 bar. Thus, the conversion of the alcohol into a mixture of ether, water and alcohol is carried out adiabatically in the presence of the dehydration catalyst and at a suitable reaction rate.

In order to raise the temperature of the alcohol-based primary fuel to the dehydration reaction temperature, the fuel must be heated from ambient temperature. It is preferably carried out as follows: indirectly exchanging heat from the pressurized fuel through a heat exchanger with hot exhaust gas from an engine prior to accumulating the alcohol-based primary fuel in the accumulator chamber.

The primary alcohol-based fuel passes from the accumulator chamber into each of the tubes connecting the chamber with the fuel injectors and comes into contact with a catalyst that catalyzes the above-mentioned alcohol dehydration reaction at a suitable temperature.

The dehydration catalyst may be provided on the side walls of the tubes in the form of catalytic hardware (catalyzed hardware) as disclosed in us patent 6,319,877, or within a reactor chamber on each of the tubes mounted between the accumulator chamber and the fuel injector.

In one embodiment of the invention, the catalyst is electrically heated to the reaction temperature.

During the engine start, the exhaust gas may be at a temperature that is not effective to heat the alcohol-based primary fuel to the necessary reaction temperature. In this case, it is preferred to include in the above-described operating method a further step of additionally heating the pressurized fuel, for example by means of an electric heater or engine heater mounted on the accumulator chamber.

The operating conditions of the process of the present invention are adjusted to achieve the desired ignition properties of the ether fuel.

The above features and aspects of the invention are explained in more detail below with reference to the figures, wherein the only one figure schematically shows a system with a common rail fuel injection unit equipped with an alcohol dehydration reactor for the method of the invention.

The compression ignition engine with common rail fuel injection system for a particular embodiment of the invention comprises a fuel tank 2 for primary fuel based on alcohol, which is connected by a line 3 to a high pressure pump 4. The primary alcohol-based fuel is pressurized in a pump 4 to a final injection pressure and is conveyed to an accumulator chamber 6 of the common rail system. The pressurized alcohol-based primary fuel is heated in a heat exchanger 8 by indirect heat exchange with hot exhaust gas 7 from an engine (not shown) before being introduced into the chamber 6.

The pressurized alcohol-based primary fuel is indirectly preheated in heat exchanger 8 to an alcohol dehydration reaction temperature, e.g., 150 ℃ to 300 ℃.

During a normal engine load cycle (load cycle), the preheated and pressurized alcohol-based primary fuel is continuously passed through accumulator chamber 6 and distributed to fuel injectors 11a, 11b, 11c and 11d via lines 9a, 9b, 9c and 9 d. The alcohol-based primary fuel is dehydrated in the presence of a dehydration catalyst disposed in each of lines 9a-9d prior to introduction into the fuel injector. The dehydration catalyst may be in the form of catalytic hardware in lines 9a-9d or as shown in the fixed bed arrangement in reactors 10a, 10b, 10c and 10 d. The primary alcohol-based fuel is partially converted by contact with the dehydration catalyst into the secondary fuel mixture described above, which includes ether, alcohol and water, and possibly gasoline.

During start-up or low load cycles of the engine, the engine exhaust gas temperature may not be high enough to provide adequate heat in the heat exchanger 8. In these engine cycles, the pressurized alcohol-based primary fuel is further heated in the accumulator chamber 8 by means of an electric heater 12 arranged in said chamber. Alternatively or in addition thereto, the catalyst may be heated by electric heating (not shown).

When the above system is continuously operating, excess primary alcohol-based fuel must be continuously withdrawn from chamber 6. This is achieved by means of a valve 14, wherein the valve 14 is hydraulically or electromagnetically operated.

The withdrawn primary fuel based on alcohol is depressurized 8 in a line 16 leading to the fuel tank 2.

The above description has been given in terms of an engine having a common rail injection system, but those skilled in the art will appreciate that the present invention is also applicable to other types of compression ignition engines.

The above description and drawings are purely schematic and otherwise conventional components and arrangements in compression ignition engines, not shown in the drawings, will be apparent to those skilled in the art.

Claims (11)

1. Method for operating a compression ignition engine using an ether containing fuel obtained by converting an alcohol based primary fuel, the steps comprising:

(a) continuously withdrawing the alcohol-based primary fuel from the fuel tank and pressurizing it to a final engine injection pressure in liquid form of the alcohol-based primary fuel;

(b) continuously introducing the pressurized alcohol-based primary fuel into a fuel accumulator chamber;

(c) continuously distributing the pressurized alcohol-based primary fuel into a tube connecting the accumulator chamber with an engine fuel injector;

(d) continuously converting at least part of the pressurized alcohol-based primary fuel into an ether-containing fuel prior to the fuel injector by contact with an alcohol dehydration catalyst in each tube disposed upstream of the fuel injector;

(e) continuously injecting the ether containing fuel into the engine at injection pressure; and

(f) continuously withdrawing a portion of the introduced alcohol-based primary fuel from the accumulator chamber; and

(g) depressurizing and recycling the withdrawn primary alcohol-based fuel to the fuel tank.

2. The method of claim 1, including the further step of preheating said alcohol-based primary fuel by indirect heat exchange with hot exhaust gas from said engine.

3. The method of claim 1 or 2, including the further step of heating said pressurized fuel within said accumulator chamber.

4. The method of claim 1, 2 or 3, wherein the alcohol-based primary fuel comprises a mixture of different alcohols.

5. The method of claim 1, 2 or 3, wherein the alcohol-based primary fuel comprises methanol and/or ethanol.

6. The method of claim 1, 2, 3, 4 or 5, wherein the primary alcohol-based fuel comprises gasoline.

7. A system for the method of claim 1, comprising

A compression ignition engine;

a fuel tank adapted to store an alcohol-based primary fuel;

a high pressure pump for pressurizing the alcohol-based primary fuel;

an accumulator chamber adapted to receive and store the pressurized alcohol-based primary fuel;

a connecting pipe for connecting the accumulator chamber with a fuel injector for injecting fuel into the compression ignition engine;

an alcohol dehydration catalyst disposed within each of the connecting tubes between the accumulator chamber and the fuel injector; and

a recirculation line for recirculating excess alcohol-based primary fuel from the accumulator chamber to the fuel tank.

8. The system of claim 6, further comprising a heat exchanger for heating the alcohol-based primary fuel by indirect heat exchange with hot exhaust gas from the engine.

9. The system of claim 7 or 8, further comprising a heating device disposed within said accumulator chamber.

10. The system of claim 7, 8 or 9, further comprising a heating device for heating the dehydration catalyst.

11. The system of claim 7, 8, 9 or 10, wherein the dehydration catalyst is provided in catalytic hardware.