1 IMPROVE ENGINE PERFORMANCE THROUGH CERAMIC COATING Lei Xia*, Ph.D. Abstract:
By applying suitable ceramic coating, the efficiency of an Internal Combustion Engine can be increased. Higher efficiency of the engine is reflected in improved performance such as reduced fuel consumption, increased power output, reduced noise and vibration, reduced oil burning, and reduced air pollution.
The ceramic material used for engine coating needs to have a low thermal conductivity; high temperature stability; matched thermal expansion coefficient with bonded metal; high wear- and corrosion-resistance; and the capability for form a durable bond with metal. I. Introduction Internal Combustion Engine (ICE) is the workhorse in modern industry and society. At the same time, an ICE consumes energy in form of fossil fuel.
To reduce energy consumption through improved engine efficiency is constant pursuit of the whole world. A large class of modern ICE such as omnipotent gasoline engine works following the Theorem of Carnot Cycle. The heart of the Carnot Cycle theorem says that an ICE works because it transfers a portion of the heat energy into mechanical work.
Further, the genius of the Carnot Cycle Theorem is that it gives the specific description for the efficiency of an engine, which is:
ŋ = 1 – Tlow / Thigh (1.1)
where: ŋ is the efficiency of the engine Tlow is the temperature of the cold reservoir
Thigh is the temperature of the hot resor Interpreting the above the Theorem one can consider that Thigh is roughly related to the average working temperature inside the engine cylinder and Tlow to the average temperature of the air discharged to the exhaust.
For an average gasoline engine, the average working temperature is 1050ºC and the exhaust temperature of 750ºC.
This according to Equ. 1.1 gives the engine efficiency of 28.6% (1-750/1050).
From the above equation, it can be seen that the engine efficiency is directly related to the working temperature of the engine. Under a limit and for the engine with a constant exhaust temperature, the higher the working temperature of the engine, the higher its efficiency.
This is the reason why engines used in racing cars and in some airspace applications have higher cooling water temperature switching setting than ordinary cars. For ordinary road cars, the thermostat temperature is usually set at 90 ºC degree C while in racing cars this could be 105 ºC and higher, resulting in an 50ºC increase of engine working temperature to 1100ºC. From Equ. 1.1, this results in a theoretical engine efficiency of 32% (1-750/1100), an increase by 12%. Please note that the above Theorem is applicable only to an ideal engine.
For a practical engine, there are many other factors that affect the performance of the engine. For example, if there is a compromise in the sealing between the engine cylinder and piston, a certain amount of thermal energy will be lost through the escape of combustant in the gap between the cylinder wall and piston.
This is also accompanied by the increased burning of engine oil and/or increased noise and vibration of engine operation. At the same time, incomplete combustion will increase pollution discharge. Therefore, to maintain a tight seal between the cylinder wall and piston; and to increase the operating temperature of the * Dr. Lei Xia has been an automobile engineer since 1989.
He worked at General Motors and now is with Hiram Engineering. Dr. Xia.
2 engine will have a beneficial effect to the engine performance. II. Engine Cylinder Condition Modern ICE cylinder consists of a steel metal insert inside the aluminum alloy body: Engine piston moves reciprocally inside the cylinder where the seal between the two is maintained by pistons rings. As the engine operation continues, the friction between the piston ring and cylinder walls invariably cause scratches, scores, pits, and other imperfection on the cylinder walls. Following photos show the conditions inside cylinder walls: These conditions on the engine cylinder cause engine performance degradation. Symptoms of performance degradation include: - Reduced power output and increased fuel consumption.
This is mainly due to the reduced compression ratio as the result of the compromised seal tightness. - Oil burning. Part of oil enters the combustion chamber and gets burned - Increased noise and vibration - Increased pollution III. Engine Ceramic Coating There has been constant search for the ideal coating material for engines to have a more endurable engine working surfaces and to improve engine performance by major engine and auto makers.
The most likely coating material is ceramics and the desired coating ceramics material should have the following properties: Lower Thermal Conductivity. Contrary to some belief, it’s better for engine cylinder wall to have low thermal conductivity with respect to cooling water rather than high conductivity. This, from Equ. 1.1., will result in higher average operating temperature, thus higher operating efficiency. This is the reason why many piston head and valve surface are coated with ceramic material with low thermal conductivity. High Temperature Stability.
The working Alu. Body Steel Insert Piston Scores, pits, and scratches Scores and scratches 3 temperature at metal material is usually below at 1200ºC, while for ceramic material it could be at 1500ºC. Again this could result in a theoretical efficiency increase by as much as 50%. Matched Thermal Expansion Coefficient. Coated ceramic needs to have a thermal expansion coefficient that is closely matched with that of the underlying metal; otherwise during the thermal cycling of operation, the bonding integrity between the metal and ceramic coating will be compromised.
Usually the thermal expansion coefficient of metal is higher than that of ceramics. Wear- and Corrosion-Resistance. In many cases there is mechanical movement occurring on ceramic coating surface such as piston movement inside an engine cylinder. The ceramic coating in these cases needs to be wear- and corrosion-resistant in order to have long operating life. Toughness. A critical drawback of most ceramic materials is its brittleness that causes low impact strength. Much effort has been put into increasing the toughness of ceramic material.
This includes reducing the ceramic particle size to nano level; change material crystal structure; and by compositing ceramic material. Toughened ceramic material has been used in piston rings. Ceramic Coating to Metal. Ceramic coating is applied to metal surface usually through two approaches:
1) high temperature deposition by melting the ceramic material which is then sprayed onto the base metal surface; and
2) using a ceramic slurry which is then sprayed, brushed, dipped or by other methods to the metal surface. IV. Zirconium Coating on Engine Cylinder Zirconium, or ZrO2, is a ceramic material that has been proved to be the most appropriate ceramic material for engine surface coating.
It meets virtually all requirements mentioned above for ideal coating material. ZrO2 has a much lower thermal conductivity than other ceramic materials. Dedicated engine research work has shown that with Zirconium coating on the engine components, the average temperature of the engine increases by 75ºC. Using Equ. 1.1, this theoretically can improve the engine efficiency by 16.4%.
The melting point of Zirconium is 2715 ºC and its creep deformation temperature is between 2400 ºC to 2500 ºC, which is higher than working temperature of virtually any ICEs. Its wear-resistibility is 15 times higher than that of Al2O3 (Alumina). The thermal expansion coefficient of ZrO2 is among ceramic materials the closest to that of steel (about 11 /x10-4 K-1).
Also much of the research work has been done for Toughened Zirconium Ceramic (TZC), which makes ZrO2 have a relative higher ductibility. Despite of these characteristics for ZrO2 that are highly desirable for metal surface coating, its uses are have been limited to piston rings, journal bearing surfaces, the coating of the valve tops. It has not been widely used for engine cylinder wall coating – the most important application deemed – at production level by engine makers. The main reason is that the ceramic coating is not entirely compatible with traditional engine making process.
After the coating is done, the cylinder bore has to be re-grinded before piston assembly can be put in. This is a time consuming process; and as a result, the added cost of ceramic coating is deemed difficult to be justified by engine makers. However, there is an elegant solution of engine Zirconium ceramic coating offered by some auto aftermarket product manufacturers. A notable example is a product called NanoEnergizer produced by Nanotec International (Korea) Company.
The product uses precious meal coated nano-size Zirconium powder emulsified in mineral oil and when applied, simply add it to the engine through oil filler port. With NanoEnergizer, the Zirconium nano powder will be brought by piston movement to all working surface of the engine during its operation.
The precious metal coating on the nano Zirconium powder facilitates the bonding of ceramic powder to the metal surface as well as helping with a cleaner combustion of air-fuel mixture. Thanks for the heat generated during normal operation of the engine, the ceramic powder attached to the engine surface is gradually cured. When the ceramic coating is completely cured, it will form a hard and smooth surface on the working components of the engine.
Because nano ceramic powder is in liquid form, it will be 4 brought to any working surface of an engine including cylinder walls, piston rings, piston top, valve tops, bearing surfaces, etc. The elegance of this solution is that it is achieved during the normal operation of the engine; there is no need for additional separate process to apply the coating; and there is no need to disassembly the engine. The effect of the NanoEnergizer coating has been tremendous.
These photos show the engine cylinder walls after the engine has run for a period of time following the use of NanoEnergizer. It can be seen that the cylinder walls now have a smooth and hard ceramic surface. And the piston rings also have matching smooth surface of Zirconium. Performance wise, there are numerous cases where after the use of ceramic coating, the engine operation has been improved in one of more of the following areas: - improved fuel economy; - increased power output; - reduced oil burning; - reduced noise and vibration; - reduced pollution discharge. V. Summary Ceramic coating, especially with Zirconium, has a beneficial effects on engine efficiency and performance. Regular use of aftermarket products based on this principle is encouraged to maintain a healthy and high-performance running engine.