Lean-Burn Engines

Lean-Burn Engines Lean-burn means pretty much what it says. It is a lean amount of fuel supplied to and burned in an engine’s combustion chamber. Gasoline burns best in standard internal combustion engines when it is mixed with air in the proportions of 14.7:1 - nearly 15 parts of air to every one part of fuel. A true lean-burn can go as high as 32:1. If internal combustion engines were 100 percent efficient, the fuel would burn and produce just carbon dioxide (CO2) and water. But the reality is, engines are far less efficient and the combustion process also produces carbon monoxide (CO),  oxides of nitrogen (NOx)  and unburned  hydrocarbons in addition to CO2 and water vapor. In order to reduce these harmful exhaust emissions, two basic approaches have been used: Catalytic converters that clean up the exhaust gases coming from the engine, and lean-burn engines which produce lower levels of emissions by better combustion control and more complete fuel burning inside the engine cylinders. Engineers have known for years that a leaner air to fuel mixture is a frugal engine. The problems are, if the mixture is too lean, the engine will fail to combust, and a lower fuel concentration leads to less output. Lean-burn engines overcome these issues by employing a highly efficient mixing process. Specially shaped pistons are used along with intake manifolds that are located and angled to match the pistons. Additionally, the engine’s inlet ports can be shaped to cause â€Å"swirl† - a technique borrowed from direct injection diesel engines. Swirl leads to a more complete mixing of fuel and air that enables more complete burning, and in the process reduces pollutants without altering the output. The downside of lean-burn technology is increased exhaust  NOx  emissions (due to higher heat and cylinder pressure) and a somewhat narrower RPM power-band (due to slower burn rates of lean mixtures). To address these problems lean-burn engines have precise lean-metered direct  fuel injection, sophisticated computer controlled engine management systems and more complex  catalytic converters to further reduce NOx emissions. Today’s advanced lean-burn engines, both gasoline and diesel, achieve noteworthy fuel efficiency performance during both city and highway driving conditions. In addition to the fuel economy advantage, the design of lean-burn engines results in a high torque power output relative to horsepower rating. For drivers, this means not only savings at the fuel pump, but also a driving experience that includes a vehicle that accelerates quickly with fewer harmful emissions from the tailpipe.

Tips to Help You Pass Chemistry Class

Tips to Help You Pass Chemistry Class Are you taking a chemistry class? Chemistry may be challenging, but there are many things you can do to help yourself succeed. Here are some tips to help you pass chemistry. Traps to Avoid So You Can Pass Chemistry Lets start out with a list of common mistakes students make which can sabotage their success with chemistry. Engaging in one or two of these may not break you, but these are dangerous practices. Avoid them if you want to pass chemistry! Thinking you can learn the math prerequisites at the same time as chemistry.Procrastinating! Putting off studying for a test until the night before, writing up labs the night before they are due, working problems the same day they are due.Skipping class.Only attending class on quiz days or leaving early.Relying on someone else to take notes.Expecting the instructor to offer extra credit or to drop a low grade.Copying the answers to the problems from someone else or from the text (for books that give the answers).Thinking a good grade early on means the class will remain the same level of difficulty or that you wont need to study later. Be Prepared for Class Chemistry is a lot harder than it needs to be if youre learning essential math skills at the same time. You should be familiar with the following concepts before setting foot in the chemistry classroom. writing and solving algebraic equationsexponentsscientific notationnegative numberslogarithmsfractions Get Your Head on Straight Some people psych themselves out of doing well in chemistry. Its not impossibly hard... you can do this! However, you need to set reasonable expectations for yourself. This involves keeping up with class and building bit by bit on what you learned the previous day. Chemistry is not a class you cram for on the last day. Be prepared to study. Take responsibility for your learning. If you are confused, let your instructor know this. Dont be afraid to ask for help.View chemistry class as an opportunity rather than a chore. Find something you like about chemistry and focus on that. Having a positive attitude can be a key to your success. To Pass Chemistry You Should Attend Class Attendance is related to success. Its partly a matter of more exposure to the subject and its partly about getting on your instructors good side. Teachers are much more understanding if they feel youve put forth an honest effort. If your grade is borderline, you wont gain the benefit of the doubt by disrespecting the time and effort your instructor put into lectures and labs. Being there is a start, but there is more to attendance than simply showing up. Arrive on time. Many instructors review concepts at the beginning of class, often indicating likely test questions and going over problems that were difficult for most of the class.Take notes. If its written on the board, copy it down. If your instructor says it, write it down. Examples are written on the board often show a method of solving a chemistry problem that is different from what you have in your textbook.Sit near the front. Its a matter of attitude. Sitting near the front engages you with the lecture, which can enhance your learning. Its easier to slack if you sit in the back. Work the Problem Sets Working problems are the surest route to passing chemistry. Dont copy someone elses work. Do the problems yourself.Dont look at the answers to problems (if available) until youve gotten an answer yourself.You may understand how a problem is worked, but dont make the mistake of assuming that is a substitute for working through the problem on your own. Work through examples yourself. Consult the worked problem if you get stuck.Write down what you are trying to answer in a problem. Write down all the facts that you are given. Sometimes seeing what you know written down this way will help you recall the method for obtaining the solution.If you get the opportunity, help someone else work problems. If you can explain the problem to someone else, theres a good chance you truly understand it. Read the Textbook The easiest way to master chemistry concepts and problems is to see examples of those problems. You can pass some classes without opening or even having the text. Chemistry is not one of those classes. Youll use the text for example and most likely will have problem assignments in the book. The text will contain a periodic table, glossary, and helpful information regarding lab techniques and units. Have a text, read it, and bring it with you to class. Be Smart on Tests You need to know the information covered by tests, but its also important to study for tests and take them the right way. Dont cram for a test. Dont put yourself in a position where you have to stay up all night studying. Keep up in class and study a little every day.Get sleep before a test. Eat breakfast. Youll perform better if you are energized.Read through the test before answering any questions. This will help you know what to expect and will allow you to identify the questions worth the most points.Be sure to answer the high-point questions. You may end up working the test backward, but thats okay. This is especially important if you are afraid you might run out of time taking the test.Review returned tests. Make sure you understand what you did wrong and how to do it right. Expect to see these questions on the final exam! Even if you never see the questions again, understanding how to get the right answer will help you master the next section of the class.