发动机工程代写 Introducing The Spark Ignition Si
A spark ignition engine is an engine that follows the thermodynamic model of the Otto cycle. Spark-ignition engines have become a huge success since the invention of the first Otto cycle engine. During its first years of production and implementation, manufacturers and engineers focused on how to increase the engine power and how to improve the engine working reliability. However due to recent findings on CO2 emissions, and the depletion the earths fossil fuel reserves, researchers have now turned their attentions towards the development of more advanced combustion systems. Thus power generation with the lowest energy input from fossil resources has become more and more important since then (Xudong Zhen, 2012). This problem has been tackled with the constant improvement and innovation of engine boosting.
13/12/12 15:52 An ideal Otto Cycle plotted on a
Pressure vs. Volume diagram, taken from
The latest trends in automobile engines are mainly focused on the design of economic, efficient and significantly less polluting cars, whilst maintaining power, torque, and driving performance (Khiar, D, 2006). Global warming and increasing fuel price are among the top public concerns and, because of this the automotive industries have had to develop various technologies to achieve this. The most cost-effective solution to this problem is engine downsizing. However, when an engine is downsized, its torque and power output is significantly reduced dues to the reduction in cubic capacity of the cylinders. This must be compensated for to suit the requirements of the vehicle for the customer. The most effective and efficient way of doing this is by utilising a pressure charging device such as a turbocharger, supercharger or EDS. (Villegas, 2011) These are methods of boosting the engine, forcing more air and proportionally more fuel into the combustion chamber of the engine, resulting in a higher magnitude power stroke from the engine.
Turbocharging is one way to boost an engine and is a very powerful means to improve fuel economy, emissions and engine efficiency (Khiar, D, 2006). A turbocharger is typically a turbine that is driven by the rejected exhaust gases from the cylinders of the engine, and this turbine in turn powers a compressor that compresses the air obtained by the air intake. The turbine is fed by the exhaust manifold, where the exhaust gases enter the turbine housing enclosing the rotor and turn the turbine (N.C.Baines, page 7 of book). The advantages of a turbocharged engine primarily are the significantly higher output of torque and power whilst reducing the specific fuel consumption. These advantages outweigh the disadvantages of this type of boosting an engine (B.E.Walsham page 39 book). When the engine is at low speed and low load, upon application of a sudden load change, the engine needs to allow time for the turbocharger to react therefore resulting in a limited acceleration or limited torque available due to the reduction in the air available in the engine cylinders (B.E.Walsham page 39 book). Turbochargers were first widely used, and still are, on large heavy trucks. The turbochargers “along with their associated intercoolers could provide the trucks with a pressure ratio of up to 2.6:1, and BMEP of 12 bar at an engine speed of 2000 RPM”. (F.J.Wallace pg 99 book). Usually to obtain a prediction of how a turbocharger is going to behave, the system and its components are usually modelled under steady state conditions due to the very small variation in behaviour of the air at the intake manifold. However at the exhaust manifold there can be significant amounts of turbulence as well as pressure pulses (D.E.Winterbone page 153 book). Benson and Scrimshaw conducted an experiment using unsteady state conditions and found that the quasi steady state method “under-estimated the results by up to 25% for power and 7% for mass flow rate” ( D.E.Winterbone page 154 book) This was then backed up by the work done by Wallace, Adgey and Blair, who used a test rig much like Benson and Scrimshaw’s but used a hydraulic dynamometer to measure the characteristics of the turbocharger turbine under pulsating conditions ( D.E.Winterbone page 154 book).
发动机工程代写 Introducing The Spark Ignition Si