Ultra-Clean Combustion Technology Combining
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SAE TECHNICAL PAPER SERIES
2001-01-0200
Ultra-Clean Combustion Technology Combining a Low-Temperature and Premixed Combustion Concept for Meeting Future Emission Standards
Shuji Kimura, Osamu Aoki, Yasuhisa Kitahara and Eiji Aiyoshizawa
Nissan Motor CO., LTD.
Reprinted From: In-Cylinder Diesel Particulate and NOx Control 2001
(SP-1592)
and
Homogeneous Charge Compression Ignition (HCCI) Combustion
(SP-1623)
SAE 2001 World Congress
Detroit, Michigan March 5-8, 2001
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2001-01-0200
Ultra-Clean Combustion Technology Combining
a Low-Temperature and Premixed Combustion
Concept for Meeting Future Emission Standards
Shuji Kimura, Osamu Aoki, Yasuhisa Kitahara and Eiji Aiyoshizawa
Nissan Motor Co., Ltd. Copyright ? 2001 Society of Automotive Engineers, Inc.
ABSTRACT
Experimental investigations were conducted with a direct-injection diesel engine to improve exhaust emission, especially nitrogen oxide (NOx) and particulate matter (PM), without increasing fuel consumption. As a result of this work, a new combustion concept, called Modulated Kinetics (MK) combustion, has been developed that reduces NOx and smoke simultaneously through low-temperature combustion and premixed combustion, respectively. The characteristics of a new combustion concept were investigated using a single cylinder DI diesel engine and combustion photographs. The low compression ratio, EGR cooling and high injection pressure was applied with a multi-cylinder test engine to accomplish premixed combustion at high load region. Combustion chamber specifications have been optimized to avoid the increase of cold-start HC emissions due to a low compression ratio. The results indicate the possibility of obtaining ultra-clean internal combustion engines capable of meeting Ultra Low Emission Vehicle (ULEV) regulations in the 21st century. INTRODUCTION
Nitrogen oxide (NOx) and particulate matter (PM) emissions of diesel vehicles are regarded as a source of air pollution, and there is a global trend to enforce more stringent regulations on these exhaust gas constituents in the early years of the 21st century. On the other hand, the excellent thermal efficiency of diesel engines is certainly a welcome attribute from the standpoints of conserving energy and curbing global warming. In considering ways of reducing exhaust emissions further in the coming century, one approach to lowering NOx and PM levels is the direct-injection (DI) diesel engine, which is advantageous for curbing CO2 emissions.
Figure 1 shows how much NOx emissions would have to be reduced for a conventional DI diesel that does not incorporate any emission reduction technologies in order to comply with current and future regulations for gasoline engines. NOx emissions would have to be reduced by 88% to meet the current standard for gasoline engines and by 96% to clear the more stringent standard set to be enforced in 2000. Moreover, a reduction of 98% would be required to reach the Ultra Low Emission Vehicle (ULEV) regulations of Tier2.
Against a backdrop of societal demands for cleaner vehicles, a great deal of research on new emission control technologies is being done today using DI diesel engines that provide high thermal efficiency. There has been a growing move in recent years to achieve radical improvements in emission performance by re-examining different forms of combustion, notably lean premixed combustion [1-6] like Homogeneous Charge Compression Ignition; HCCI. This HCCI combustion has been the focus of much interest for significant reducing NOx and soot. HCCI with the early injection can reduce NOx emissions by 90-98% in comparison to conventional Diesel combustion. However, HC and CO emissions are high level and fuel consumption deteriorates [6]. In HCCI combustion technology, a formation of homogeneous condition avoiding fuel-wall interaction is the biggest subject for achieving high thermal efficiency, reducing HC emission and avoiding oil dilution. Furthermore, the injection timing significantly influences exhaust emissions and fuel consumption. The main challenges of this combustion are controlling the onset of combustion [7]. The authors have used a high-efficiency DI diesel engine to originate a new combustion concept called Modulated Kinetics, which simultaneously reduces NOx and smoke levels by reconciling low-temperature combustion with premixed combustion[8-10]. The first generation of the MK concept was applied to develop a new type of DI diesel engine. At present, research is under way on the second generation of MK combustion aimed at expanding the region where this combustion concept is used in order to improve emission performance further. This paper describes the emission characteristics of the second generation MK combustion concept that applied the prolonging ignition delay and the shortening injection
duration. The combustion chamber specification was optimized to reduce the HC emissions under the cold condition. The results indicate the possibility of obtaining ultra-clean internal combustion engines for the Ultra Low Emission Vehicle (ULEV) regulation of California at the 21st century.
Figure 1.NOx Reduction Rate Requirements of
Regulations
BASIC CONCEPT OF MK COMBUSTION
The MK concept can be essentially characterized as a low-temperature, premixed combustion system that is aimed at simultaneously reducing NOx and PM emissions, which is a major issue for DI diesel engines. The basic concept of MK combustion is explained schematically in Fig. 2.
Because NOx formation is strongly dependent on the combustion temperature, one effective way to reduce NOx emissions is to lower the combustion temperature. Low-temperature combustion is accomplished in the MK combustion concept by applying heavy exhaust gas recirculation (EGR) to reduce the oxygen concentration. Usually, reducing the oxygen concentration, however, results in a higher smoke level. Since it was concluded that a higher smoke level would be unavoidable with diffusion combustion, an investigation was made of a premixed combustion process, marking a departure from the methodology pursued previously. An attempt was made to reduce NOx and smoke emissions simultaneously through the use of low-temperature combustion and premixed combustion, respectively.
For premixed combustion, the fuel and oxygen must be thoroughly mixed prior to ignition. In the MK combustion concept, sufficient mixing time is secured by prolonging the ignition delay, and dispersion of the injected fuel is promoted to accomplish premixed combustion. The fuel injection timing is retarded so as to correspond to the prolonged ignition delay. A toroidal combustion chamber shape has been adopted for the purpose of promoting dispersion of the injected fuel outside the piston cavity. Additionally, a higher swirl ratio is generated to suppress the formation of HCs and soluble organic fraction (SOF). Experimental results have further confirmed that this combustion system is effective in reducing cooling losses [8,9]. It thus also incorporates a measure to counteract the deterioration of fuel consumption due to a decline in the degree of constant volume which is a side effect induced by retarding the fuel injection timing.
Figure 2.Schema of Modulated Kinetics (MK)
Combustion
CHARCTERISTICS OF COMBUSTION AND EXHAUST EMISSIONS WITH MK COMBUSTION COMBUSTION PHOTOGRAPHS – The main specifica-tions of the single-cylinder test engine used in the experi-ments are given in T able 1. Combustion conditions were observed on the basis of high-speed photographs to con-firm that the MK concept works to promote low-tempera-ture, premixed combustion in a DI diesel engine. Photographs of MK combustion are compared in Fig. 3 with those of the conventional DI combustion process, typified by no EGR and a standard injection timing and swirl ratio. The heat release rate curves measured for each combustion process are also given in the figure. Looking at the heat release rates, it is seen that the onset of heat release with the MK concept was plainly later than for the conventional combustion process, owing to the large retardation of injection timing. Another characteristic of MK combustion is the low heat release rate following the onset of heat release. This is attributed to the low rate of increase in cylinder pressure, which is thought to lead to a reduction of combustion noise. Although the initial heat release rate was low with the MK concept, combustion subsequently proceeded vigorously and the overall combustion period was virtually comparable to that of the conventional combustion process. Moreover, the general shape of the heat release rate curve for the MK concept shows a single stage of entirely premixed combustion. This is in clear contrast to the two-stage profile observed for the standard DI process, which is divided between an initial stage of premixed combustion and the main stage of diffusion combustion.
In the combustion photographs for the MK concept, virtually no clear sign of a brilliant flame is observed
throughout the entire combustion period. By analogy with
the high transparency of the flame, this is taken as proof not only of the weak luminous intensity of the flame but also of its low soot concentration on account of the low combustion temperature. Although the reduced combustion temperature cannot be substantiated directly from the photographs, they are thought to confirm a more advanced state of premixing, which was the original aim.
T able 1. Specifications of T est Engines
Figure 3.
Comparison of Heat Release Rate and Combustion Photograph
PERFORMANCE CHARACTERISTICS – The effect of each combustion factor in the MK concept on exhaust emissions and thermal efficiency is shown individually in Fig. 4. With a lower oxygen concentration, NOx emissions were dramatically reduced by approximately 90%, and retarded injection timing reduced the smoke level markedly. Moreover, it is seen that the higher swirl ratio played a part in reducing smoke and unburned HC emissions. Figure 4 shows the effect of each combustion factor on thermal efficiency. With a lower oxygen concentration, which has a pronounced effect on reducing NOx emissions, the thermal efficiency improved, however the thermal efficiency was deteriorated with retarded injection timing. A higher swirl
ratio improved the thermal efficiency over the level of ordinary combustion.
Figure 4.
Effects of Each Combustion Factor on
Exhaust Emissions and Thermal Efficiency
SECOND GENERATION OF MK COMBUSTION
CHALLENGES FOR MK COMBUSTION – The foregoing discussion has presented the fundamental characteristics of the low-temperature, premixed MK combustion process, based on experimental results obtained with simulated EGR gas. T ests conducted with a multi-cylinder engine using actual EGR gas also verified that MK combustion could be achieved in the low-load region in nearly the same manner as with the single-cylinder engine and the simulated EGR gas. The first generation of the MK combustion system was successfully implemented in a new four-valve-per-cylinder DI diesel engine (YD25) that was put on the market in June 1998 [10].
The application of MK combustion over a wide operating range is seen as an effective way to improve the emission, noise and vibration performance of small DI diesel engines for the 21st century. T wo essential conditions for accomplishing MK combustion are the use of heavy EGR and the complete injection of all fuel prior to ignition. The region of application for the first-generation MK combustion system is shown
schematically in Fig. 5 along with the target for the second-generation system. In the high-load region where the EGR gas temperature rises, MK combustion cannot be accomplished with the first-generation system because the ignition delay is shortened. The target set for the second-generation system aimed at reducing exhaust emissions further is to accomplish MK combustion at least throughout the entire 10-15 test mode region corresponding to the range of everyday driving.
In trying to apply MK combustion to the high-load region, it is predicted that two problems will have to be resolved, as outlined in Fig. 6. The first problem is that the ignition delay is shortened by the higher temperature of the EGR gas. The second problem is that the injection duration is prolonged by the greater quantity of fuel injected. The multiplied effects of these two problems make it impossible to complete the injection of all fuel prior to ignition, which is one of the necessary conditions for accomplishing premixed combustion.
Consequently, as indicated in the figure, there are two approaches that can be considered for expanding the MK combustion region to the high-load range. One approach is to prolong the ignition delay and the other approach is to shorten the injection duration. The fundamental objective of prolonging the ignition delay is to lower the gas temperature of the combustion field at top dead center (TDC) of the compression stroke. Specific ways of accomplishing that objective include cooling the EGR gas and lowering the compression ratio. On the other hand, the injection duration can be shortened with high-pressure injection or a larger nozzle hole, among other approaches.
Figure 5.MK Combustion Region of First generation (YD25DDT) and T arget
RELA TIONSHIP BETWEEN IGNITION DELAY AND INJECTION DURA TION – The specifications of the four-cylinder DI diesel engine used in the experiments are given in T able 2. An EGR gas cooler was provided in the EGR pipe running from the exhaust turbine inlet to the intercooler exit downstream of the intake air compressor. This EGR gas cooler was a water-cooled system that allowed the water circulation volume and water temperature to be adjusted. A piezoelectric sensor was fitted to the cylinder head to measure the cylinder pressure. Moreover, a dilution tunnel was used to measure PM emissions. A common rail injection system was adopted which allowed the injection pressure to be adjusted as desired, making it possible to achieve high-pressure injection even in the low speed range.
In order to expand the MK combustion region to the high-load range under a condition of heavy EGR, the ignition delay must be longer than the injection duration. The effects of high-pressure injection, a reduced compression ratio and EGR gas cooling, which were the approaches taken here to expand the MK combustion region, on the relationship between the injection duration and ignition delay are shown in Fig. 7. These results were obtained near the maximum load level of the 10-15 test mode under the conditions of a constant injection timing and EGR rate. For the baseline engine with the first-generation MK combustion system, the difference between the injection duration and the ignition delay was a short interval of slightly more than ten crank angle degrees. This difference was progressively shortened by the application of each approach, and the combination of all three approaches resulted in an ignition delay that was longer than the injection duration. Under these conditions, it was then confirmed that the ignition delay exceeded the injection duration for all of EGR rates described in the following section.
Figure 6.Approach for Expanding the MK Combustion Region
T
able 2.Specifications of T est Engine
Figure 7.
Effects of Injection Pressure, Compression Ratio and EGR Cooling on the Relation
between Injection Duration and Ignition Delay
COMBUSTION CHAMBER SPECIFICATION – The fore-going discussion has shown that a combination of a lower compression ratio, high-injection pressure and EGR gas cooling can prolong ignition delay than injection duration in the high-load region. However, it was feared that a lower compression ratio might cause HC emission performance to deteriorate in cold-condition. Ordinarily,the effective approach to reduce HC emission in cold-condition is the avoiding fuel-cavity wall interaction. A small nozzle hole is one way to avoid the fuel-wall inter-action, however this leads prolonging injection duration,which is an opposite tack of MK combustion. So, the large cavity diameter is used to avoid HC emissions in cold-condition.
Fig. 8 and T able 3 shows the piston configuration used this test. Compression ratios were maintained 16. Fig. 9compares HC emissions as function as coolant temperature. HC emissions under hot-condition did not change on account of the large cavity diameter. Under the cold-condition, coolant temperature was 313k, HC emission with the large cavity diameter was significantly reduced. According to this results, the following experiments were conducted using the large cavity diameter.
Figure 8. Sections of T est Pistons
Figure 9.
Effect of Enlarging Cavity Diameter on Cold-Start HC Emission
EMISSION PERFORMANCE IMPROVEMENT OF SECOND GENERATION MK COMBUSTION
SMOKE CHARACTERISTICS – The foregoing results indicated that the combination of low compression ratio,EGR cooling and high injection pressure could make the ignition delay longer than the injection duration. An attempt was then made to achieve MK combustion over nearly the entire load range by substantially changing the ignition delay as a result of cooling the EGR gas. The results obtained are shown in Fig. 10, which presents a map indicating the effect on the smoke concentration of the difference between the injection duration and the ignition delay and the excess air ratio λ. The data were obtained under conditions of an engine speed of 2000rpm and 6 bar break mean effective pressure (BMEP). It is seen that smoke increased with a smaller λ value in the region of a short ignition delay, i.e., the area where the horizontal axis values are greater than zero. The smoke level shows an especially sharp increase at λ values below 1.2. By contrast, the smoke level decreased in the
region where the ignition delay exceeded the injection T able 3. Specification of T est Pistons
(A)
(B)
Cavity Shape T roidal
Cavity Diameter 47.2 mm 56.1 mm (Cavity Diameter / Bore)
(53%)(63%)Cavity Depth
19.8 mm 15.0 mm
(A)Standard Cavity (B)Large Diameter Cavity
duration, and even at λ values below 1, the smoke level was less than 1 BSU. These results indicated that smoke generation can be suppressed even in the region near a stoichiometric mixture ratio by making the ignition delay longer than the injection duration.
Figure 10.Effects of Prolonging Ignition Delay on
Smoke Level
COMPARISON OF PERFOMANCE BETWEEN CONVENTIONAL AND MK COMBUSTION – Figure 11 compares the emission performance between MK combustion, which make the ignition delay longer than the injection duration, and conventional combustion. The injection pressure and air excess ratio of both specification were kept 1600 bar and 1.3. MK combustion produces NOx emissions that are below 0.3 g/kWh without significant increase of PM and fuel consumption. In contrast, it is seen that the PM levels with conventional combustion increase sharply when NOx level fall below 2 g/kWh. As a results of this increase of PM, it is difficult that NOx level with conventional combustion is reduced below 1 g/kWh.
Figure https://www.360docs.net/doc/e716915558.html,parison of NOx, PM and BSFC between Conventional and MK Combustion
The NOx reduction rate and particulate emissions on conventional and MK combustion are compared in Fig.
12. The conventional combustion was run with several injection pressure levels, from 700 to 1600 bar. Looking at the NOx reduction rate (NOx/NOx baseline), NOx of NOx reduction rate with conventional combustion is from 90 to 92 %.
Figure 12.Emission Comparison: MK Combustion vs.
Conventional DI Diesel
The heat release rate of MK combustion and conventional obtained under a condition of the lowest oxygen concentration is shown in Fig. 13. The heat release rate curve shows a single-stage profile with gradual heat release in the initial combustion period. This type of profile characterizes the heat release rate of MK combustion. From this result as well, it is concluded that the attainment of MK combustion worked to reduce the smoke level.
The extension of MK combustion to the high-load range in this study showed that NOx emissions could be reduced by more than 98% over the entire range of everyday driving without having a large adverse effect on smoke formation and fuel consumption. Furthermore, the second-generation MK combustion system with the excess air ratio limit expanded to near the stoichiometric air-fuel ratio level without increase of smoke has a latent possibility for using the NOx catalyst.
Figure https://www.360docs.net/doc/e716915558.html,parison of Heat release Rates between Conventional and MK Combustion
Figure 14. T est Car Results with second-generation MK Combustion and 5way Catalyst
The test car results with second-generation MK combustion and 5way catalyst are shown in Fig. 14. The 5way catalyst consists of the oxidation catalyst, particulate filter and De-NOx catalyst. In this experiment, NOx adsorber is used for De-NOx catalyst. The sulfur content of the fuel is maintained below 10ppm. According to the test car results, the combination of second-generation MK combustion and 5way catalyst has the possibility of meeting the ULEV emission (NOx<0.07g/ mile, PM<0.01g/mile) with 5000 lbs. gross vehicle weight rating (GVWR).
At the present time, however, this system is still at the research level and there are numerous issues that remain to be resolved, including the cooling capacity of the EGR gas cooler and measures for controlling cold-start HC emissions. Nevertheless, the fact that this study confirmed a diesel engine has the potential to achieve emission levels comparable to those of a gasoline engine is a significant result, even though it was obtained at the research level.
CONCLUSION
This paper has proposed a low-temperature, premixed combustion concept, referred to as the MK concept, which is designed to achieve simultaneous reductions in the NOx and smoke emissions of a small DI diesel engine. With the aim of expanding the MK combustion region, a multi-cylinder test engine was used to confirm the effect of combining a low compression ratio, high-injection pressure and EGR gas cooling. The results made the following points clear.
1.The combination of a low compression ratio, high-
injection pressure and EGR gas cooling can make ignition delay longer than injection duration.
2.In cold-condition, the large cavity is effective to avoid
the increase of HC emission due to low compression ratio.
3.It was confirmed that the smoke concentration could
be reduced to less than 1 BSU in the operating region near a stoichiometric air-fuel ratio with the ignition delay longer than injection duration.
4.NOx reduction rate of MK combustion is over 98%
and the limit of NOx reduction rate with conventional combustion is from 90 to 92 %.
REFERENCES
1.Allen W. Gray and Thomas W Ryan, “Homogeneous
Charge Compression Ignition(HCCI) of Diesel Fuel”, SAE Paper NO.971676, 1997.
2.Iida N., “Alternative Fuels and Homogeneous Charge
Compression Ignition Combustion T echnology”, SAE Paper NO. 972071, 1997.
3.Furutani M., Y. Ohta, M. Konno and M. Hasegawa,
“An Ultra-Lean Premixed Compression-Ignition Engine Concept and Its Characteristics”, Proceedings of the Fourth International Symposium COMODIA 98, pp.173-177, 1998.
4.T akeda Y., K. Nakagome and K. Niimura, “Emission
Characteristics of Premixed Lean Diesel Combustion with Extremely Early Staged Fuel Injection”, SAE Paper 961163, 1996.
5.Y anagihara H., Y. Sato and J. Mizuta, “A Study of DI
Diesel Combustion under Uniform-Higher Disparaged Mixture Formation”, The 13th International Combustion Engine Symposium Lecture, 1996, pp. 365-369 [in Japanese].
6.Akagawa H., T Miyamoto, A. Harada, S Sasaki, N.
Shimazaki, T Hashizume and K. Tsujimura,“Approaches to Solve Problems of the Premixed Lean Diesel Combustion”, SAE Paper NO. 1999-01-0183,1999.
ULEV
7. Rudolf H. Stanglmaiar and Charles E. Roberts,
“Homogeneous Charge Compression Ignition(HCCI): Benefits, Compromises, and Future Engine Applications”, SAE Paper NO. 1990-01-3682, 1999.
8.Y. Matsui, S. Kimura and M. Koike, “A New
Combustion Concept for Small DI Diesel Engines -1st Report : Introduction of the Basic T echnology -”, JSAE Paper 9730416 [Japanese].
9.S. Kimura, Y. Matsui and M. Koike, “A New
Combustion Concept for Small DI Diesel Engines -2nd Report : Effects on Engine performance -”, JSAE Paper NO. 9735051[Japanese].10.S. Kimura, O. Aoki, H. Ogawa, S. Muranaka and Y.
Enomoto, “New Combustion Concept for Ultra-Clean and High-Efficiency Small DI Diesel Engines”, SAE Paper 1999-01-3681(1999)FISIT A 96
11.Y. Mase, J. Kawashima and T. Sato, “Nissan’s New
Multi-valve DI Diesel Engine Series”, SAE Paper 981039(1998).
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2018-06-02: Task 2 (India) Some people use technology to take advice for their medical problems rather than seeing to doctor. Why is this so? Is it positive or negative development according to you? 范文1： Owing to technology, everything becomes easily accessible. Some people take advantage of technology as they discuss their health issues with experts on the internet rather than going to them. This trend increasing in our society as people have a busy schedule. In my opinion, it is a positive development as taking medical prescription online save time as well as energy. But it has some disadvantages also so discussed below. Technology brings people close enough that they can discuss their problems with a number of people at once and can share their experiences so that others can take advantage of this. Taking online prescription save time, as there is no need to run to the hospitals and set a queue to meet the doctors. Using technology, people can take advice from foreign experts rather than considering only native ones. Various online websites are now available, where experts and people can communicate with each other, here https://www.360docs.net/doc/e716915558.html, is worth mentioning as it provides a common platform for everyone. However, it may have some disadvantages, as in serious health issues such as cancer or in other deadly diseases where the doctor can visually check and do some tests, is not possible online. In those cases, people should visit the experts and get proper medical care. Under specialist vision, the patient gets recover much faster. Although technology provides us various advantages, sometimes under certain circumstances, it may worsen the situation. For example, in case of heart attack patient should rush to the hospital rather than taking online medical care. In some medical issues such as cold, fever people should take advice online but in other deadly cases, people should visit to doctors so that can take better medication. In conclusion, no doubt technology has a huge role and brings everything closer, it has its own merits and demerits, we can take only certain medication and healthcare pieces of advice such as what we should eat to reduce the weight, not in other serious issues. 范文2： Many individuals are making use of technology such as the internet to seek medical advice instead of visiting a doctor. There are many reasons behind this, however, in my opinion, it is a negative development.
科技作文之雅思大作文科技类
雅思大作文科技类 【篇一：雅思写作科技类满分范文解析,必看!】 雅思大作文考试题材多样，考生要想取得高分就要对每一种题材都有所了解并掌握技巧。今天，就以科技文为例，一起来学习雅思写 作科技类满分范文解析吧。相信通过学习，你会了解一篇满分作文 怎样写才会投考官所好，拿到满分。 科技类最常见的话题类型有两种： 1，科技产品评价及未来发展 即“科技产品怎么样，以后会怎么样”的问题;具体包括对现有科技产品的评价(优劣势分析、是否合乎道德标准和对个人、企业、国家以及整个社会的影响)和自己预想以后会出现什么样的产品或现有产品会出现什么样的功能以及未来的影响。 2，科技产品作为媒介 即“怎么用”的问题;具体包括现代通讯技术使人类足不出户便能操作网络购物、电视购物、网上银行、视频会议等，人类使用手机的利弊，互联网传播信息的好处与弊端，网上翻译软件盛行因此还有没 有学习外语的必要。 要评价一篇文章的优劣势，首先还是让我们熟悉一下writing task 2即大作文的评分标准。 (1) task response (tr) whether all parts of the task are addressed whether a viewpoint is clearly expressed, developed and supported. (2) cohesion and coherence (cc) whether the response has a suitable layout and logical ordering of points(文章是否条理清晰，行文有逻辑) correct and appropriate use of connectives (是否正确使用衔接词) (3) lexical resources (lr) range and accuracy of vocabulary (词汇丰富度和准确度) https://www.360docs.net/doc/e716915558.html, the correct form and spelling of the words (词汇形式和拼写正确) (4) grammatical range and accuracy (gra) the range and accuracy of tenses and sentence structure (时态和句式的丰富度和准确度)
雅思大作文科技
Online shopping is now replacing shopping in the store. Do you think it is a positive or negative development? 立场：线上和线下商店共存才是良性发展，否则很可能是消极发展 网购优势: 1. 从不同线上渠道货比三家 2. 足不出户，即可收到商品 3. 网上价格更具竞争力 劣势： 1. 无法触摸 2. 需要等待一段时间才能收货 线下购物优势： 1. 无需等待，即可收货 2. 通过近距离观察，触摸，更清晰的判断是否值得购买 In many instances, online shopping is now replacing store shopping. Some people view this as s positive development; other people view it as a negative development. Although the benefit of online shopping are certainly understandable, it is my feeling that it will be a negative development if many retail stores are forced to close due to competition from online shopping sources. The advantage of online shopping are obvious. People can read reviews on those items and can compare prices from various sources on the internet. Without even leaving their home, they can order and receive online products, often at prices which are similar or even lower than the prices they would receive in a retail store. So, the benefits of online shopping are undeniable. That being said, retail stores also offer advantages that are undeniable. Retail stores allow people to touch, feel, and maybe even demonstrate the product, in front of customers. For example, if a person is interested in purchasing a smartphone works, a salesperson can walk him through. Also, ordering groceries online means that customers will not be able to touch or feel those fruits, as they would if they purchased those items in the supermarket. Moreover, not everyone is patient enough to wait for their orders for a few days whereas they can receive these items immediately in a real store. There is no doubt as to why online shopping is becoming more and more popular. However, retail shops offer benefits which are not available with online shopping. It remains to be seen how much online shopping will affect people's retail shopping options, but I think people will be better served if both options remain available. Some people think that with the increasing use of mobile phones and computers, people lose the ability to communicate face to face. To what extent do you agree or disagree? 立场：同意
雅思大作文--technology
雅思写作Task2：科技篇(technology) 自2010年以来，科技类的写作考察率飙升。这一类作文的话题涵盖广泛，并且如果要拿高分，就需要用到一些冷门的词。 真题一览： 1.Nowadays cheap air travel is increasingly popular in the world. To what extent do you think its advantages outweigh its disadvantages?（如今，价格低廉的打折航空旅游已经在世界范围内越来越为人们所接受。对此，你认为在何种程度内打折的航空旅行是利大于弊的？） 2.Some people think space travel is important. Others think people will not remember this. Discuss both views and give your own opinion.（有些人认为太空旅行时间十分重要的事情。也有人认为人们不会铭记这些太空旅行。请讨论双方的观点并给自己的看法） 3.Modern technology is increasing the gap between the rich and poor. To what extent do you agree?（现代科技使得社会中贫富差距不断被拉大。对此，在何种程度内你同意这个观点？） 4.Long distance flight consumes natural resources and pollutes the air. Some people think it should be banned. To what extent do you agree or disagree.（长距离飞行会耗费大量自然资源并对大气造成污染。有人认为应该禁止长距离飞行。对此，你在何种程度上同意或不同这个观点？） 5.Some people think food has been changed by technological advances and this is an improvement while others worry that is harmful. Discuss both sides and give your opinion.（有些人认为伴随着科技的进步，人们的食品也不断发生着变化，而这时一种积极的变化，而另外一些人则担心这种变化有害。请评论这两种观点并给出自己的看法。） 6.There are many problems associated with mobile phones today. To what extent the advantages of mobile phone outweigh the disadvantages?（如今手机与很多麻烦问题联系在一块。你认为在何种程度上手机是利大于弊的？） 7.Today, people can work and live almost anywhere they want to because improvement of communication technology and transportation. Do advantages of this development outweigh the disadvantages?（如今，由于通信技术和交通的迅猛
IELTS 9分考官范文-科技类
Life was better when technology was simpler. To what extend do you agree or disagree? 9’考官范文 Modern technology has revolutionized life in three main fields: work, transport and communication. Although modern technology is often blamed for stress and alienation, I doubt that many people would want to turn back the clock to the pre-technological age. Despite the fact that life was simpler in former times, I would prefer not to return to that lifestyle, because that simplicity was due to a lack of choice. Before large jet airliners came in in the 1960s, for example, air travel was beyond the reach of most people. Before electronic cash registers, people had to spend a lot of time on math calculations to carry out transactions. Furthermore, our knowledge of the world around us, especially foreign countries, was sketchy before television brought us the vivid images of documentaries. Modern technology has brought liberation from the exhausting and boring labour and has set us free to enjoy more interesting work and leisure. It is not even always true that modern technology is more complex to use than it was to perform household chores. Caring for a horse was a far more complicated and time-consuming matter than starting up a car and taking it to the petrol station. One has only to read novels from past times to realize the anxiety and frustration that resulted from transport systems limited to the speed of a horse. The examples I have given are just a few of the many that can illustrate the case that modern technology makes life more convenient. Probably what makes some people yearn for the good old simple days is that the speed of modern technology forces us to speed up our pace of life. But sometimes this change can be resisted, when we set simple priorities and stick to them.
雅思写作高分范文-科技类5篇
科技类 1.Some people think that robots are very important for humans’ future development. Others, however, think that robots are a dangerous invention that could have negative effects on society. Discuss both views and give your opinion. The field of science and technology has advanced throughout the past decades and has changed our perspectives of life. Among those advancements, robots have become significant by trying to get close to human lives. While some people argue that though these robots have managed to solve most of our day-to-day problems, they can still create problems, I believe that robots are significant for humans’ current and future development. It is normal for people to be worried about the rise of robotics in every aspects of our lives. In workplace, one of the real impacts humans face is the loss of jobs and the economic displacement of workers. As prices continue to drop for advanced technology, the result is that robots cost less than a human does to complete the same job. Consequently, wages are slashing and pay inequality is worsening. Moreover, when societies become too dependent on robots, humans become lazy and begin to lose the skills that they has replaced. Last but not the least, it’s not a stretch to imagine that untrustworthy robots may cause over-trust issue and deception. As anthropomorphic robots come to the physical world, people, children particularly, are susceptible to telling their deepest, darkest secrets to these robots whose cute faces may hide exploitative code. Nevertheless, the benefits that robots bring about could outweigh these potential risks. Many robotic solutions have been introduced in order to help disabled people. For example, wheelchairs, robotic arms, and many other robotic devices are created to help the disabled to perform their day-to-day tasks. Moreover, some of the greatest technologies are now in medicine, particularly with robot surgeons. In addition, robots are used in many high end factories to make their production lines more efficient and time saving. Compared with humans, robots rarely make mistakes and are more precise. As long as they have power, they can work continuously without any pauses or breaks and does not get tired as humans. In conclusion, there are good aspects as well as bad aspects about robots being a part of our lives. As long as humans remember that it is we who
雅思高分范文 科技类
ordinary people more than recent technological developments. To what extent do you agree or disagree? 以前的科技发展比现在的科技发展更使普通人民受益吗 2 There are social, medical and technical problems associated with the use of mobile phones. What forms do they take? Do you agree that the problems outweigh the benefits of mobile phones? 手机会有社会健康和技术问题吗、。都是什么问题。问题大于益处吗 3 Leisure is a growing industry, but people no longer entertain themselves as much as they used to because the use of modem technology has made them less creative. Do you agree or disagree with this statement? 随着科技的发展，人变得没有创造力，不像以前那样会娱乐自己了吗 4 Television has had a significant influence on the culture of many societies. To what extent do you think television has positively or negatively affected cultural development? 电视对社会文化的影响积极还是消极 5 Some people think that modern technology is increasing the gap between the rich and the poor. To what extend do you agree with their opinion? 科技加大贫富差距吗 6 When a country develops its technology, the traditional skills and ways of life die out. It is pointless to try to keep them alive. To what extent do you agree or disagree with this opinion? 传统技术和生活方式会因为国家的科技发展而灭亡。而保护它们是没有意义的、你同意吗 7 Life was better when technology was simpler. To what extend do you agree or disagree? 当科技更简单的时候生活更好吗 8 Many people ignore basic science today, what are the causes and what are your solutions? 为什么现在人民忽视基础科学。解决方法？ 9 The production and transportation of food has been heavily influenced by modern technology. To what extent do you think this is a positive development? 食物的生产和运输被科技极大地影响。积极还是消极 10 Nowadays cheap air travel is increasingly popular in the world. To what extent do you think its advantages outweigh its disadvantages? 廉价机票流行的优点和缺点谁大 11 Modern technology is creating one single world culture. To what extent do you agree or disagree？ 现代科技创造一个单一的世界文化，你同意吗 12 Traditional games are more useful than modern games in developing children’s skills. To what extent doyou agree? 传统游戏币现代游戏更好的发展小孩的技能，你同意吗
雅思写作范文：传统与科技
文都国际教育官方网站：https://www.360docs.net/doc/e716915558.html,/ 雅思写作范文：传统与科技 随着出国留学人数的增多，雅思成为众多学子出国留学考试中的选择。本文文都国际教育小编为了帮助大家更好的备考雅思写作，为大家介绍雅思写作范文：传统与科技，跟随小编一起看看吧！ Some people believe that technological developments lead to the loss of traditional cultures. I partly agree with this assertion; while it may be true in the case of some societies, others seem to be unaffected by technology and the modern world. On the one hand, the advances in technology that have driven industrialisation in developed countries have certainly contributed to the disappearance of traditional ways of life. For example, in pre-industrial Britain, generations of families grew up in the same small village communities. These communities had a strong sense of identity, due to their shared customs and beliefs. However, developments in transport, communications and manufacturing led to the dispersal of families and village communities as people moved to the cities in search of work. Nowadays most British villages are inhabited by commuters, many of whom do not know their closest neighbours. On the other hand, in some parts of the world traditional cultures still thrive. There are tribes in the Amazon Rainforest, for example, that have been completely untouched by the technological developments of the developed world. These tribal communities continue to hunt and gather food from the forest, and traditional skills are passed on to children by parents and elders. Other traditional cultures, such as farming communities in parts of Africa, are embracing communications technologies. Mobile phones give farmers access to information, from weather predictions to market prices, which helps them to prosper and therefore supports their culture. In conclusion, many traditional ways of life have been lost as a result of advances in technology, but other traditional communities have survived and even flourished. 以上就是小编与大家分享的雅思写作范文：传统与科技的全部内容，希望对参加雅思考试的考生有所帮助。最后，预祝大家能在雅思考试中取得理想中的成绩，顺利赴海外求学深造。 文章来源于文都国际教育：https://www.360docs.net/doc/e716915558.html,/kaopei/ielts/yszl/78.shtml 文都国际教育官方网站：https://www.360docs.net/doc/e716915558.html,/