Compression rate reduction process by adding cold material at the cylinder head of engines converted to natural gas to be used as fuel

Abstract

One of the processes needed for the conversion of a diesel engine so that it can use natural gas as fuel is the reduction of the compression ratio, since the one that the diesel engine originally has is greater than the one needed for the optimal operation with natural gas. The proposed process consists of adding cold material to the cylinder head or engine head through metallization or electric arc or plasma spraying to form a combustion chamber therein.

Claims

1. A process for converting a diesel internal combustion engine having a cylinder head, a combustion chamber, a sealing surface and valve seats to natural gas, the process comprising: a) performing compression ratio calculations for obtaining the combustion chamber volume required for a gas-fuel engine; b) removing the cylinder head of the internal combustion engine; c) adding cold material into the cylinder head of the internal combustion engine by a metallization process on the sealing surface, protecting thus an area of the valve seats by forming an additional combustion chamber; d) subjecting the modified cylinder head of the internal combustion engine to a machining process, which will allow the combustion chambers and the sealing surface to be polished; e) reinstalling the modified cylinder head of the internal combustion engine.

2. The process for converting an engine according to claim 1, wherein the metallization process is performed by arc-spraying.

3. The process for converting an engine according to claim 1, wherein the metallization process is performed by plasma spraying.

4. The process for converting an engine according to claim 1, wherein in step e) if the engine contains a camshaft on0 the cylinder head a lightener is adjusted so that cam belts will not be tighten more than necessary.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the arc spraying process where the sprayed metal reaches the base material by an sprayed jet passing through an electric arc.

(2) FIG. 2 describes the plasma spraying process wherein the sprayed metal reaches the base material after passing through an arc generating a dust spray suspended in a carrier gas and reaching the base material by a spray stream.

(3) FIG. 3 shows the final result of the finished combustion chamber and the machined surface after the polishing of the combustion chamber and surface machining.

(4) FIG. 4 shows the process of reducing the compression ratio by means of adding cold material in the cylinder head for converted engines.

DETAILED DESCRIPTION OF THE INVENTION

(5) The process proposed in the present invention allows the conversion of a diesel engine to natural gas by adding cold material to the cylinder head.

(6) The process described in the present invention consists in increasing the size of the combustion chamber on the engine head by adding cold material, this process decreases the costs and process times compared to the extraction of material from the pistons, besides not affecting the structural reliability of the engine and being easily reversible, and compared to that of the separation sheet is the reliability of the engine since the sheet is usually a very thin element that is likely to fail, while the addition of material to the cylinder head behaves as a single piece, i.e., as the original element.

(7) In order to carry out this process, the calculations are initially conducted to know the filler thickness needed so as the desired engine have the compression ratio required to optimally work with the new fuel. The calculation for determining the filler thickness uses the following formula:

(8) $e_r-\frac{V_{\mathrm{oil}}+V_{\mathrm{cam}}\left(1-R_{\mathrm{cf}}\right)V_{\mathrm{emp}}\left(1-R_{\mathrm{cf}}\right)}{\left(R_{\mathrm{cf}}-1\right)**\frac{d^2}{4}}$
wherein:

(9) d: cylinder diameter; c: career; e: packing thickness;

(10) $V_{\mathrm{oil}}=*c*\frac{d^n}{4};$
Vcam volume of the combustion chamber that the piston has and the cylinder head is obtained by supplying a fluid from a calibrated cylinder until these volumes are completely filled, it is advisable to use an acrylic or the like in the upper part with a perforation where the fluid can be added, and the deposited amount thereof corresponds to the volume of the camera (Vcam);

(11) $V_{\mathrm{emp}}=*e*\frac{d^2}{4};$
RCf is the one that the engine must have to operate with natural gas as fuel, this value is between 12 and 16 depending on the characteristics of each engine (12-14 for supercharged engines and 14-16 for natural aspiration engines).

(12) The engine head is then disassembled according to the particular specifications given by the manufacturer. Subsequently, the addition of the cold material is carried out by a process known as metallization or spraying. This process can be carried out by arc spraying or plasma spraying, as indicated in FIGS. 1 and 2, respectively.

(13) In a preferred embodiment, the process of adding the cold material by electric arc spraying comprises compressed air (1), a power supply (2), which allows the compressed air (1) to pass through an electric arc (3) so that a sprayed jet is produced (4), wherein the sprayed material (5) is deposited on the base material (6). This process can be observed in FIG. 1.

(14) In another preferred embodiment, the cold material addition process is performed by plasma spraying, wherein a DC power supply (7) is connected to a coolant circulation (8) through which a plasma gas (9) passes through an electrode (10). The plasma gas 9 then passes through an arc (11) where it is mixed with a dust jet suspended in a carrier gas (12) producing a plasma flame (13) in a nozzle (14) which in a spray stream (15) deposits the sprayed material (16) onto the base metal (17). This process can be observed in FIG. 2.

(15) The cold material and the conditions required to carry out the cold material addition by arc spraying or plasma spraying will depend on the specifications given by the manufacturer for each type of engine to be converted and, therefore, of the material of the cylinder head on which the process will be performed. Also, this step from the process claimed will also depend on the equipment and the reference thereof with which the addition of the cold material is carried out, since the conditions may vary according to the specifications given by the manufacturer. In this way, a person with average skills in the art would understand that the development of the step of adding cold material will be subject to the specific conditions of the equipment used to convert the desired engine.

(16) In general terms, in the spraying process the cylinder head should be brushed, and then covered with tapes and special products so as to prevent it from being adhered with the sprayed material, such as in the chamber to be formed, lubrication and cooling ducts, among others, then a layer of base material is sprayed and then the filler material. The result of this process is the formation of a combustion chamber on the seal surface of the cylinder head protecting the area of the valve seats, as seen in FIG. 3. It is important to note that after this process the cylinder heads must be completely flat, that is why the cylinder head must then go through a machining process where the finishing of the combustion chambers is polished and the finish of the sealing surface is also polished; the final result is as shown in FIG. 3. By completing the process, the cylinder head is reinstalled in the engine, bearing in mind that if the converted engine has a camshaft over the cylinder head, the adjustment plate must be modified so that the timing belt does not overtighten as described in FIG. 4. Considering the reversible nature of the process described in the present invention, if the engine is required to be use fueled again with diesel, it is possible to carry out a process called brushing, so that the added material can be easily removed.

(17) As shown in the final finish (FIG. 3) the resulting cylinder head is a single solid part that works just like the original one, with no thin and weak elements between the cylinder head and the cylinder block failing easily, and without pistons weakening. FIG. 3 shows the finished combustion chamber (18) and the machined surface (19) in the cylinder head of the engine. In fact, the process described in the present invention allows to repair significant buckling or wear problems on cylinder heads until they are fully recovered. Likewise, and without causing any problems, the process claimed has been applied to competition engines, wherein said engines are highly pushed to the limit as they are supercharged with turbo-compressor. In contrast, and by employing processes similar to those disclosed in the state of the art, where separation sheets or irreversible modification of the piston are employed in order to reduce the compression ratio, there were no satisfactory results presenting drawbacks in a 40% of cases where they were tested.

(18) Differences in this process, with respect to the process conventionally performed, are mainly based on the reliability of the operation of the engine that was modified, and it has to be also taken into account that the process where the engine pistons are modified by removing material requires the engine to be completely taken apart and the need of more elements, which entails a greater cost and time, compared to the process discussed in the present invention. In addition to the above, the proposed process can be easily reversible, i.e., the engine will be able to run again with diesel as fuel, since it only requires removing the material added to the cylinder head by means of a brushing process, which is a process well known by a person skilled in the art.