ENGINE SYSTEM WITH REFORMER

An engine system includes a reformer for driving an engine by supplying the engine with a reformed fuel which the reformer reforms from a pre-reformed fuel. The reformer includes a reforming catalyst for reforming the pre-reformed fuel by a water vapor reforming reaction. The engine system also includes a pre-reformed fuel supply adjustment unit for supplying the pre-reformed fuel to the reformer. The reformer includes an extremity portion provided in an engine cylinder. The pre-reformed fuel supply adjustment unit supplies the pre-reformed fuel to the reformer during a suction stroke of the engine, and the reformed fuel is directly supplied from the reformer into the engine cylinder.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1is a first configuration diagram of this system. A reformer1is installed in an engine head in the vicinity of an exhaust valve7of an exhaust pipe9, or at the exhaust pipe immediately behind the engine head. A pre-reformed fuel3is supplied to the reformer1from a pre-reformed fuel tank3via a pre-reformed fuel supply adjustment unit11. Here, the reformer1is installed adjacent to an engine combustion chamber via an exhaust valve7which also functions as a reformed fuel supply adjustment unit. According to this configuration, a combustion gas right after exhausted from an engine cylinder10is supplied to the reformer1, resulting in supply of an engine exhaust heat at high temperature.

The exhaust valve7also functions as a reformed fuel supply adjustment unit to supply the reformed fuel into the engine cylinder10. Normally, since an accidental fire, and decrease in engine efficiency are caused by supplying the exhaust gas into the engine by more than a predetermined amount, supplying the exhaust gas into the engine cylinder10by more than the predetermined amount will become a problem. In order to solve this problem, a backflow preventer12is installed at a downstream side of the exhaust gas of the reformer1. This prevents the exhaust gas of the exhaust pipe at a downstream side of the reformer1from being supplied to the engine cylinder10when the reformed fuel is supplied from the exhaust valve7into the engine cylinder10. For this reason, when the reformed fuel is supplied to the engine cylinder10, the exhaust gas is supplied not more than the predetermined amount. An open/close valve can be used for the backflow preventer12. At this time, when the pre-reformed fuel is supplied to the reformer1, the open/close valve is closed so as to prevent the reformed fuel from being exhausted to a downstream.

A fuel supplying unit13to supply the pre-reformed fuel3is installed at the a suction pipe8of the engine so that the pre-reformed fuel can be supplied to the engine cylinder10without passing through the reformer1. In addition, an oxygen concentration detecting unit17to detect an oxygen concentration in the exhaust gas is installed at the exhaust pipe9of the engine. An excess coefficient of the engine is controlled based on the oxygen concentration detected by the oxygen concentration detecting unit17. An air flow adjustment unit18to adjust an air amount is installed at the suction pipe8of the engine. In addition, operations of the suction valve6, the air flow adjustment unit18, the exhaust valve7, the pre-reformed fuel supply adjustment units11and13, the open/close valve, and a pump4, etc. are controlled by an electric controlling unit (not shown).

Also, a pressure detecting unit15to detect a pressure in the engine cylinder10is installed. The pressure detecting unit15may be an axial torque sensor of the engine, or a detecting unit using an ion current, which can estimate the pressure in the engine cylinder10. Also, a pressure sensor14to measure a pressure in the exhaust pipe is installed at a downstream side of the reformer1of the exhaust pipe9. Since both of the exhaust gas and the pre-reformed fuel pass through the reformer1, a contact surface area with the exhaust gas is increased by using a honeycomb structure as shown inFIG. 2. Also, a catalyst is supported by the exhaust gas contact surface so that a reforming reaction occurs at the exhaust gas contact surface. By using the above structure, a reaction flow path doubles as an exhaust gas flow path, and a water vapor in the exhaust gas of the engine becomes to be available in the reforming reaction. Also, the catalyst in the reformer1is a zeolitic catalyst. Also, the reformer1may increase the exhaust gas contact surface area by using a structure such as a porous structure, a fin structure, or a microspace, etc. Also, the catalyst of the reformer1is a noble metal including at least one or more elements of nickel, ruthenium, platinum, palladium, rhenium, chromium, and cobalt, and a carrier is a simple substance of any one of, or a mixture of, alumina, titania, silica, and zirconia. Also, the reformer1may increase the exhaust gas contact surface area by using the porous structure, the fin structure, or the microspace, etc.

By using the system configuration as shown inFIG. 1, the following effects can be obtained:

1. By using the water vapor in the exhaust gas for reforming, hydrogen in the water vapor can be used as the fuel,
2. A high temperature exhaust gas can be supplied to the reformer,
3. A high temperature EGR and the reformed fuel can be supplied into the engine cylinder,
4. A negative pressure during a suction stroke of the engine can be used for the reforming reaction,
5. There is no need to add a line for the reformed fuel, and
6. The reformed fuel never liquefies partially.

With respect to the effect 1, for example, assuming that the pre-reformed fuel is a gasoline, C8H18(normal octane), which is one of components in the gasoline, can cause a water vapor reforming reaction as follows.

The above reforming reaction is an endothermic reaction, and hydrogen in the water vapor can be used as a fuel. Therefore, it is found that a heat value of the reformed fuel is larger than that of the pre-reformed fuel by 1303 kJ. Since the heat value of the pre-reformed fuel is 5075 kJ and that of the reformed fuel is 6378 kJ, the heat value of the reformed fuel is more improved than that of the pre-reformed fuel by 25.7%. That is, it means that the reforming reaction improves a heat efficiency by 25.7% with reference to C8H18.

With respect to the effect 2,FIG. 3shows a relationship between an equilibrium temperature of the reforming reaction (1) and a conversion rate. According toFIG. 3, it is found that the higher the reforming temperature, the higher the reforming efficiency.FIGS. 4 and 5show exhaust gas temperatures at a gathering portion of exhaust manifolds on the downstream side of the exhaust pipe and at a position immediately behind an engine outlet, which are mapped using an engine revolution number and an engine torque in order to compare to each other, respectively. According toFIGS. 4 and 5, it is found that the nearer to the engine, the higher the exhaust gas temperature, and that a change in the exhaust gas temperature depending on an operating condition of the engine is small. From the above, by installing the reformer1in the exhaust pipe in the vicinity of the exhaust valve of the engine or in the engine head as shown inFIG. 1, an exhaust gas having higher temperature can be supplied to the reformer1, and the reforming efficiency of the reformer1can be improved. Also, since the exhaust gas having higher temperature can be supplied to the reformer1, various fuels such as the gasoline, alcoholic fuels such as a methanol and an ethanol, etc., an alicyclic hydrocarbon, and an aromatic hydrocarbon, etc., can be reformed, and various kind of fuel can be used.

With respect to the effect3, an explanation will be given. By using the configuration shown inFIG. 1, the reformed fuel can be supplied from the exhaust valve7. At that time, since the water vapor in the exhaust gas is used for reforming, a high temperature EGR gas is supplied to the engine cylinder10together with the reformed fuel.FIG. 6shows a relationship between an EGR rate and an adiabatic flame temperature at the time when an excess coefficient of a mixture supplied into the engine cylinder10is equal to 1. The EGR gas temperatures are compared at 25□ and 800□. According toFIG. 6, it is found that when the EGR rate is increased, an inert gas is increased and the adiabatic flame temperature is lowered, and that the higher the EGR gas temperature is, the more lowering of the adiabatic flame temperature is suppressed. That is, it means that lowering of the exhaust gas temperature of the engine associated with increasing in the EGR rate can be suppressed. When the water vapor in the exhaust gas is used for reforming, the EGR gas is mixed with the reformed fuel, However, by using the configuration shown inFIG. 1, the EGR gas temperature can be raised, lowering of the exhaust gas temperature can be suppressed, and the reforming efficiency at the time when the EGR gas is supplied can be improved. Next,FIG. 7shows an EGR rate of the mixture in the engine cylinder10in the horizontal axis, and a laminar flow combustion rate (SL) in the vertical axis. At that time, the mixture temperatures are compared. Since the combustion rate affects a degree of constant volume of the engine, it is an important factor to improve the heat efficiency.FIG. 7shows that the lower the EGR rate is and the higher the mixture temperature is, the higher the laminar flow combustion rate is. That is, even if the EGR rate is high, the combustion rate can be improved by raising the mixture temperature. Since the high temperature EGR gas can be supplied to the engine by using the configuration shown inFIG. 1and the mixture temperature can be raised compared to the normal temperatures of the EGR gas, the combustion rate can be improved and the degree of constant volume can be improved.

With respect to the effect4,FIG. 8shows the relationship between the equilibrium temperature and the conversion rate at the time of the reforming reaction of the chemical formula (1) by comparing reforming reaction pressures. In the reaction represented by the chemical formula (1) in which number of molecules increases after reforming, the lower the reforming reaction pressure is, the higher the conversion rate is. By using the configuration shown inFIG. 1, since a negative pressure during a suction stroke of the engine can be used for the reforming reaction, the reforming efficiency is increased, the amount of recovered waste heat is increased, and the heat efficiency of the engine is increased

With respect to the effects 5 and 6, in such a configuration disclosed in the patent document 1, since the reformed fuel is supplied from the reformer1to the suction pipe8, it is necessary to newly install a pipe used for the reformed fuel. Also, by installing the pipe used for the reformed fuel, the gasoline which was not reformed in the reformed fuel is cooled at the midway of the pipe and may liquefy partially. As opposed to the above, by using the configuration shown inFIG. 1, since the reformed fuel is supplied from the exhaust pipe9of the engine to the engine cylinder10, the pipe for the reformed fuel is not needed. Also, since the reformed fuel is supplied into the engine cylinder before the reformed fuel is cooled, the problem of partial liquefaction of non-reformed gasoline does not arise.

Next, a controlling method in the first configuration diagram will be explained. In a first configuration, the engine is controlled so that the engine is operated near the excess coefficient of about 1.FIG. 9shows a relationship between the excess coefficient and the adiabatic flame temperature. As shown inFIG. 9, it is found that the closer the excess coefficient approaches to 1, the higher the adiabatic flame temperature is. That is,FIG. 9shows that the exhaust gas temperature is raised. For this reason, the reforming efficiency in the reformer1is improved, and the heat efficiency is improved. Next,FIG. 10shows a relationship between the excess coefficient and a purification rate of a three-way catalyst. According toFIG. 10, in view of the purification of the exhaust gas, it is found that the operation on condition that the excess coefficient is about 1 is optimal.FIG. 11shows a relationship between a laminar flow combustion rate and the excess coefficient. According toFIG. 11, the laminar flow combustion rate is maximized at a point where the excess coefficient is slightly lower than 1. Also, when oxygen exists in a reforming reaction chamber of the reformer1, the pre-reformed fuel is oxidized at the time of reforming, thereby generating heat. Therefore, an endothermic value at the time of reforming is decreased, resulting in lowering of the heat efficiency. For this reason, the operation is performed on condition that the excess coefficient is equal to or less than 1 so that oxygen does not exist in the exhaust gas. For these reasons, in the first configuration, the operation on condition that the excess coefficient is equal to 1 is optimal. In order to realize this condition, at least one of controlling an air flow adjustment unit18installed in the suction pipe8, controlling an amount of the pre-reformed fuel supplied to the suction pipe8, and controlling an amount of the pre-reformed fuel supplied to the reformer1is performed so that an oxygen concentration in the exhaust pipe9is within a predetermined range.

Next, an open/close timing of the exhaust valve and a supply timing of the pre-reformed fuel will be explained.FIG. 12shows histories of a lift amount of the exhaust valve7, a control signal to the pre-reformed fuel supply adjustment unit11, and ΔP at each stroke of the engine. ΔP is defined as described below.

ΔP=pressure in engine cylinder−exhaust pipe pressure

During an exhaust gas stroke of the engine, the exhaust valve7is lifted, an exhaust gas in the engine cylinder10is exhausted to the exhaust pipe9, the exhaust gas is supplied to the reformer1, and the reformer1is warmed. After that, during a suction stroke of the engine, when the ΔP becomes a negative pressure, the exhaust valve7is opened again, and a supply instructing signal is input to the pre-reformed fuel supply adjustment unit11. By controlling as described above, since ΔP is the negative pressure, the pre-reformed fuel is supplied from the pre-reformed fuel supply adjustment unit11to the reformer1, the pre-reformed fuel is reformed in the reformer1, and the reformed fuel is supplied to the engine cylinder10via the exhaust valve7together with the exhaust gas. At that time, since there is a time lag in supplying of the reformed fuel from the reformer1to the engine cylinder10, supplying of the pre-reformed fuel from the pre-reformed fuel supply adjustment unit11to the reformer1is stopped during a suction stroke before the exhaust valve7is closed. Also, the suction valve6is opened after the exhaust valve7is closed. This is because the reforming reaction can be occurred in the reformer1at low pressure by opening only the exhaust valve7so as to supply the reformed fuel, and the reforming efficiency is improved.

Next, an operating method without supplying the pre-reformed fuel to the reformer1will be explained. Since the reforming temperature in the reformer1is low at the time of starting or warming-up of the engine, the reforming efficiency is lowered as shown inFIG. 3. For this reason, the pre-reformed fuel is prevented from being supplied to the reformer1, and the pre-reformed fuel can be supplied to the engine cylinder10by the fuel supplying unit13without passing through the reformer1. At the same time, since the exhaust valve7is controlled so as not to open at the suction stroke, the EGR gas is prevented from being mixed into the engine. By operating as described above, warming-up time of the reformer1is shortened, thereby enabling an operation with high reforming efficiency.

Next,FIG. 13shows a second configuration. An adjustment valve16, which is adjusted to be opened at a differential pressure equal to or greater than a predetermined differential pressure, is installed at a pipe connecting the pre-reformed fuel tank3to the reformer1. Since a backflow preventer12of the exhaust gas makes the pressure in the reformer1to be negative during the suction stroke of the engine, a differential pressure occurs between the pre-reformed fuel tank3and the reformer1. This differential pressure causes the pre-reformed fuel to be supplied to the reformer1. At this time, the adjustment valve16prevents the pre-reformed fuel from being supplied to the reformer1after the exhaust valve7is closed. Also, the air amount supplied to the engine cylinder10is adjusted by the air flow adjustment unit18. The air flow adjustment unit18may be a valve mechanically adjusting the air flow.

Compared to the first configuration, a second configuration does not need the pre-reformed fuel supply adjustment unit or the electric controlling unit, and the pre-reformed fuel can be supplied to the reformer1mechanically. Therefore, the number of parts and cost of the system are reduced, and the reformed fuel can be supplied from the exhaust valve7to the engine cylinder10reliably. In the second configuration, when a ratio of a supply amount of the pre-reformed fuel supplied to the engine cylinder10to a suction air amount is adjusted, by adjusting the open/close timing or the open/close lift amount in addition to the supply amount of the pre-reformed fuel and a throttle opening of the exhaust valve7, a reformed fuel supply amount to the air amount supplied to the engine cylinder10becomes to be adjustable.FIG. 14shows a method for adjusting the open/close lift amount of the exhaust valve7. By changing the lift amount and the open/close timing of the exhaust valve7continuously or stepwise as described above, the supply amount of the pre-reformed fuel can be adjusted. Also, a reformed fuel supply amount supplied into the engine cylinder10may be adjusted by adjusting the adjustment valve16in order to adjust a pre-reformed fuel supply amount supplied to the reformer1. Also, in the second configuration, when the temperature of the reformer1is lower than a predetermined temperature (e.g., at the time of starting of the engine, or warming-up of the reformer1), or when the reformer1is out of order, a pipe supplying the pre-reformed fuel to the suction pipe8without passing through the reformer1may be provided. Here, for example, the predetermined temperature is a temperature at which a dopant ratio is equal to or less than 10% when the fuel is reformed in the reformer1. As methods for detecting a temperature, a method for directly detecting the temperature in the reformer1, or a method for detecting the exhaust gas temperature to estimate the temperature in the reformer1may be used.

Next,FIG. 15shows a third configuration. In the third configuration, the pre-reformed fuel supply adjustment unit11supplies the pre-reformed fuel to the reformer1, and the reformer1is provided in the engine cylinder10. For example, the pre-reformed fuel supply adjustment unit11may be a gasoline direct-injector, and the reformer1may be provided in the gasoline direct-injector.

Compared to the first configuration, by using the third configuration, there is no need to modify the engine drastically, and the number of parts can be reduced. Also, since the reformer1is provided in the engine cylinder10, the reformed fuel can surely be supplied to the engine cylinder10. Specifically, in the controlling method, since the reaction pressure at the time of reforming can be lowered by supplying the pre-reformed fuel to the reformer1during the suction stroke, the reforming efficiency is improved (seeFIG. 8). Further, as shown inFIG. 16, by opening the suction valve6after the pre-reformed fuel is supplied to the reformer1by the pre-reformed fuel supply adjustment unit11during the suction stroke, the reforming reaction pressure in the reformer1can be lowered, and the reforming efficiency is improved.

EXPLANATION OF REFERENCE SYMBOLS