Internal-combustion engines – Charge forming device – Heating of combustible mixture
Reexamination Certificate
2003-12-02
2004-09-14
McMahon, M. (Department: 3747)
Internal-combustion engines
Charge forming device
Heating of combustible mixture
C123S549000, C123S179210
Reexamination Certificate
active
06789530
ABSTRACT:
OBJECT OF THE INVENTION
The present invention relates to a series of improvements introduced in the cold start system of diesel engines, whereby an optimisation is achieved of said starting in the ambit of unitary cylinder capacities of the order of 200 to 650 cubic centimetres.
The object of the invention is the development of a system for the uniform heating of the intake air flow in direct-injection diesel engines of small unitary cylinder capacity through an electrical resistance, in the form of a continuous and optimally distributed tape in the section of passage of said fluid, to achieve the starting of such engines at temperatures below −10° C. and without impairing the performance of the engine in conditions of maximum power operation as a consequence of a high head loss in the heating element.
BACKGROUND OF THE INVENTION
High-speed direct-injection diesel engines employed in motor vehicles and with unitary cylinder capacities of the order of 200 to 650 cubic centimetres, are being used massively in substitution of the divided-chamber or indirect-injection engines, mainly due to the smaller specific consumption of direct-injection engines.
Also, with relatively high supercharging pressures and due to the new concept of fuel injection systems at constant pressure, it is possible to obtain specific powers of the order of 60 kW/l, which makes that type of diesel engine very competitive when compared with petrol engines.
However, one of the main problems with diesel engines is associated with cold starting, especially in severe climates where ambient temperatures usually attain very low levels, so that to overcome said drawback or problem, high-speed direct-injection diesel engines use glow plugs (electrical resistances) located, through the head, inside the combustion chamber of the engine, to provoke the self-ignition of the fuel that is present on the surface of said spark plug which in turn initiates the engine combustion process. However, although such a solution is accepted practically universally, it in turn presents a series of drawbacks, problems and difficulties due to three fundamental concepts that can be summarized as follows:
1.—Reduced reliability, through being an element subjected to high mechanical and thermal stress.
2.—Difficulty in location, due to the use in a widespread way of the concept of four valves per cylinder in new-generation diesel engines, so that this solution leaves scant margin for manoeuvring in locating the preheating spark plugs, bearing in mind that the location should assure their interaction with the fuel jet, allow accessibility from the exterior and guarantee an adequate thermodynamic design of the head, a problem that can be augmented by the demand for greater specific powers while simultaneously reducing emission levels.
3.—Influence on the combustion process, since once its function in cold starting has been carried out, the preheating plug is an obstacle located inside the combustion chamber that hinders the process of mixing the air with the fuel, disturbing the range of air speeds and inevitably worsening engine performance, like a poor combustion process for example. Also, in diesel engines of the type described the size of the chamber is reduced and high injection pressures are employed, which leads to a greater number of injector nozzles, to assure a good fuel atomisation, which in turn leads to an improvement in the mixing process and therefore in the combustion. However, the presence of the preheating plug inside the chamber produces an unavoidable interaction with the injection jets that finally imposes a limit to all the improvements introduced in the process, as a consequence of an incomplete combustion process.
To overcome the drawbacks of cold starting in diesel engines it is possible to employ the concept of heating the intaken air by means of a heat source that can be a flame or an electrical resistance as is described in the U.S. Pat. No. 4,512,322. However, these solutions, as they have been conceived, are only possible to apply to the case of engines with unitary cylinder capacities above 800 cubic centimetres, since these engines are more adiabatic and therefore have smaller heat losses. Engines with smaller unitary cylinder capacities require more optimised systems, both from the point of view of heat energy transfer and of head losses. For this reason, it is essential in these engines to perform a uniform heating of the intake air along the entire section of fluid passage, an aspect which is inconceivable with the solution proposed in the patent mentioned, since due to the arrangement of the heating element, the heating would only be achieved in a very small portion of air concentrated in the central area, there still remaining around this an important quantity of air at a very low temperature, which means a very low thermal efficiency in achieving appropriate air temperatures for cold starting in motor vehicle engines. Moreover, the direct drawback associated with a heater distributed over the orifice section of the fluid passage relates to the loss of pressure produced, which in small engines constitutes a critical aspect regarding their performance at high running speeds. This demands a hydrodynamic design of the heater that is far removed from that proposed in the U.S. Pat. No. 4,685,437, a solution conceived with the goal of achieving more uniform air temperatures than with the above-commented solution (U.S. Pat. No. 4,512,322) but with unacceptable values of head loss in small engines under operating conditions different to cold starting.
In the Spanish Patent of Invention 9900616 a diesel engine cold starting system is foreseen also based on performing a preheating of the orifice intake air load, said preheating of the air being carried out before the latter reaches the combustion chamber of the cylinders of the engine. The electrical resistance or resistances are arranged before the intake manifold and/or preceding the intake valves of the engine, so that when the heating energy losses through the walls of the manifold are low, either because the corresponding intake manifold is of a material with low thermal conductivity or for other reasons, generally a single electrical resistance (
7
) is fitted for the preheating, which is located at the inlet of said manifold, whilst if the losses through the walls are high, for example because the manifold is of a material with high thermal conductivity, a series of electrical resistances are fitted immediately before the inlet of each of the cylinders of the engine.
DESCRIPTION OF THE INVENTION
The improvements object of the present certificate of addition, applicable to the Patent of Invention 9900616 mentioned in the last paragraph of the previous section, supposes a higher functional efficiency of said system, by achieving less resistance to the passage of the air, which implies a smaller head loss, and a greater contact surface between the heating element and the air, which improves the heat transfer.
For this reason and in a more specific manner the improvements of the invention consist essentially in the use as heating medium of an electrical resistance in tape form, optimally distributed over the section of fluid passage and in the direction of the flow, whereby a uniform temperature of the air charge is achieved that the cylinder breathes adequate for starting the engine at low temperatures, as well as perfectly acceptable levels of head loss for the engine under other operating conditions.
It has also been foreseen that the support for fastening the tape resistance to the engine incorporates in diametrically opposed areas of the external mouth of the orifice for the passage of air to the engine, individual groups of recesses of approximately semicircular configuration, with a nipple inside, defining grooves having an arched trajectory in which are mounted and fastened the inflections of the laminar resistance, with the interposition of respective ceramic insulators, there also being two special slots, one blank and lacking an insulator for f
Broatch Jacobi Jaime Alberto
Desantes Fernandez José Maria
Navalon Carretero Herminio
Payri Gonzalez Francisco
Katten Muchin Zavis & Rosenman
McMahon M.
Nagares, S.A., Universidad Politecnica de Valencia
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