New technology to achieve high efficiency of diese

New technologies to achieve high efficiency of diesel engines

automobile manufacturers are now faced with the task of developing engines that meet increasingly stringent regulations on emissions and fuel efficiency, while trying to meet higher performance (i.e. high power) requirements. For example, in the United States, cars must not only pass more and more stringent smoke emission standards, but also the vehicle fuel economy standard (CAFE) shows the increasing attention to fuel economy. This paper will discuss two technologies that can help automobile engine manufacturers approach these goals - laser texturing of cylinder liner and precision drilling of fuel injector nozzle. We will also provide durability test data on Audi diesel engine, which shows that laser treatment of cylinder liner can greatly reduce friction and wear by up to 89% and fuel consumption by up to 75%

diesel engine and mechanical wear

diesel engine has low fuel consumption, so it is widely used outside the United States, from cars to heavy trucks. However, in the United States, diesel engine has not been widely used in private cars, mainly because people mistakenly believe that its performance is lower than that of gasoline engine. In addition, the lack of low sulfur diesel in places such as California is also an important reason why diesel engines cannot be widely used

diesel engines require a higher compression ratio (up to 30:1) than gasoline engines to ignite fuel without spark plugs. Therefore, even light diesel engines use cast iron cylinder liners to cope with high mechanical stresses. This high compression makes piston ring/cylinder wear and friction more prominent, which limits the performance of current diesel engines and the ability to improve engine performance. For example, a simple way to improve the performance of diesel engines is to further improve the compression ratio. However, due to the friction, sealing and wear between the piston ring/cylinder liner interface, the possibility of doing so is limited at present

how big a problem is the friction between piston rings/cylinder liners? In internal combustion engines, most of the combustion energy is lost in the form of heat to the cooling system. About 15% of the remaining available power becomes mechanical loss due to friction between the engine and the drive chain. In diesel engines, up to 60% of mechanical losses are caused by friction between piston rings and cylinder walls. Therefore, it is estimated that reducing this friction loss by only 10% can reduce fuel consumption by 3%. In today's era of slow improvement of engine efficiency, 3% is a great benefit. From the long-term implementation of Ningbo new material Park, upstream and downstream cooperation in the industrial chain and the introduction of capital, this wear will also cause the wear of piston rings and cylinder sleeves, reduce engine performance, increase emissions and improve fuel consumption

progress of laser surface treatment technology

although carbon dioxide laser has been used to harden cast iron cylinder liner since the early 1970s, until now, no one has used high-energy ultraviolet (UV) laser pulse to treat cylinder liner in a large area. In Audi, we have conducted extensive research on the effect of UV laser surface treatment with a four cylinder, 1.9-liter (81 kW) turbocharged direct injection (TDI) diesel engine. We also conducted further research on a V6 diesel engine. Before conducting laser surface experimental research, we manufactured cylinder liners and installed them in the usual (industry standard) way. The only difference is that we use laser surface treatment instead of the final mechanical polishing (honing) step

for surface treatment, we put the engine set on a specially built Workstation - equipped with a high pulse energy excimer laser (lambda Physik lambda steel 1000), with a wavelength of 308 nm and a pulse duration of 25 ns. The laser can produce 1 joule/pulse energy with a pulse repetition rate of 300Hz. The maximum stable average power is 300 watts. On this workstation, the laser beam is guided to the cylinder (located in the engine block) through the beam transmission system. The last optical element is a rotating mirror placed inside the cylinder, which reflects the light beam onto the cylinder wall. The optical element can move axially to scan the light beam along the length of the cylinder wall. Coordinated with the rotation of the engine set, the beam can scan along the circumference. During laser irradiation, auxiliary gas nitrogen is applied to the cylinder surface. The scanning system was developed in cooperation with Germany's arges industrieplanung und Lasertechnik GmbH

after processing the experimental cylinder liner in this way, we collected two types of data. Most importantly, we accelerated the upgrading of plastic granulator technology and conducted life cycle and durability experiments. On the dynamic test-bed, we adopt the standard fatigue protocol designed to simulate multi load cycle: the 4-cylinder TDI engine is operated for 602 hours; the engine speed changes at full load; When the load changes, the engine speed changes; Full load/low load transition; Startup/shutdown transition, etc

during these tests, we monitored the engine performance. We also took scanning electron microscopy (SEM) photos to examine the surface morphology of the cylinder after laser treatment at the microscopic level. In addition, we also took a section from the upper part of the cylinder of a TDI engine after 800 hours of operation. The cross section was analyzed by transmission electron microscope (TEM)

reduce wear - Tribological interpretation

the results obtained from TDI engine fatigue experiment are very dramatic, as shown in Figure 1. Compared with the mechanically honed cylinder liner, the wear of the cylinder wall is reduced by 23 ~ 89% depending on the load cycle. The corresponding wear of piston ring is reduced by 30% ~ 88%. For the V6 engine, the fuel consumption was reduced by 75% during the 800 hour test

Figure 1 The wear reduction of excimer laser treated cylinder and conventional honed cylinder (1.9 L/81 kW r movable baffle can not vibrate the pin on the reversing switch 4tdi diesel engine)

at the end of the "wear" phase of the initial 4000 hours, both the piston ring and cylinder liner decreased by almost 90% in terms of

wear characteristic curve

SEM and TEM micrographs show that the significant improvement of the performance of these engines is due to three phenomena caused by laser: surface hardening caused by surface modification, surface smoothing and oil storage performance

TEM microscopic data show that a very hard material surface layer similar to nitride layer is generated by excimer laser and nitrogen assisted gas. Even after 800 hours, TEM data showed that this material existed on the inner wall surface of the cylinder. It also indicates the presence of fine iron structures containing carbon and nitrogen particles. This assumption seems to be confirmed by the data of UV hardening. TEM data also confirmed that laser annealing can smooth the surface. In particular, honing can cause traces and creases in the graphite layer on the surface of cast iron. The laser process appears to eliminate these surface irregularities

although the combination of harder and smoother surfaces can certainly reduce friction and wear, we believe that the surface modification effect also plays a major tribological role in the significant effects observed. Figure 2 shows SEM images of cylinder liner surface after ordinary mechanical honing and laser treatment. Honing causes random, staggered, interconnected surface grooves that retain oil. However, these grooves can act as a connecting system of channels, allowing the pressure and movement of the piston ring to push the oil out, so that rough (sharp surface metal to metal) contact can be made

Figure 2 SEM photos of inner surface morphology of cylinder liner: (a) surface after traditional mechanical honing (pay attention to staggered groove structure)

(b) the surface is machined first and then irradiated with ultraviolet laser. Photo source: GJL

while the laser treatment process will open the pre-existing graphite shell, resulting in many micro pits or pits on the surface that can capture oil. Because these pits or pits are not interconnected, there is no escape for the oil, and the piston ring will slide on the captured oil droplets, as shown in Figure 3. Obviously, this condition is very close to the ideal goal of hydroelastodynamic (all fluid) lubrication. The size of the pit is very important. The pit must be large enough to play this sliding role, but not large enough to produce any "oil leakage". The precise pit size is Audi's proprietary technology

Figure 3 Tribological explanation of reducing friction: (a) interconnected groove system generated by mechanical honing; (b) The micro hydrodynamic structure produced by laser processing

drilling technology of fuel injector nozzle

determines the efficiency of diesel engine. On the other hand, we are still in the early stage of development in the new laser drilling technology of fuel injection process

ideally, the fuel injector should evenly fill the engine cylinder with diesel oil with fine suspension. This can be achieved by forcing pressurized fuel through tiny holes in the injector tip, which is made of quenched steel with a general thickness of 1mm. Traditionally, these holes are formed by electrical discharge machining (EDM). A typical ejector nozzle has up to 12 holes, and the hole diameter is generally in the range of 150 ~ 200 microns

recently, the US Environmental Protection Agency mandated that the diesel engine industry must meet stricter fuel efficiency standards by 2007 and even more stringent standards by 2010. In addition, the allowable soot and NOx emission standards must be reduced to 90% of the 1988 standards. Meeting these goals requires improving combustion efficiency, which in turn requires redesigning the injector nozzle to provide a smaller droplet size. In particular, we studied how to reduce the aperture (e.g. as small as 50 microns) and increase the nozzle thickness. Increasing the nozzle thickness is very important because to force the fuel through these holes, the nozzle must be able to withstand higher pressure. In addition, the shape of the hole is also under study. The most striking one is the hole with inverted cone angle. To solve these problems, it is very difficult to adopt EDM technology, and it is easy to use laser technology

fine drilling ideally requires a laser beam with TEM00 mode, which can be easily aggregated into small spots. Then, the hole is processed either by impact drilling (where the hole diameter is equal to the beam diameter) or by spiral drilling (where the small beam is scanned in a spiral shape, which is basically a casing processing method). We believe that both methods will eventually find a place in this application. Impact drilling is relatively simple, the cost of implementation is relatively low, and the processing time per hole can be less than 0.5 seconds. However, through properly focused optical components and careful control of the movement of the tip/beam, it is possible to generate holes with inverted cones and/or custom shapes

for this application, pulsed lasers with high peak power and high beam quality are required, because they form clean holes with the lowest chip. Fortunately, diode pumped all solid state laser with TEM00 beam characteristics has now grown into a reliable industrial tool in other precision drilling applications, such as