LEARNING SCIENCE THROUGH ACTIVE LEARNING 5-9 June 2013 Valdepenas - Spain The use of 5E method in the study of heat engines

Physics, 10‘th grade, Topic : heat engine

Engage Object, event or question used to engage the students. Let’s look at these types of cars without which we couldn’t imagine the century of speed. What do we know about the construction and functioning of heat engines?

ENGAGE Connection facilitated between what students know and can do.  The definition of the heat engine – brainstorming  The classification of heat engines according to: the combustion time : with external combustion and internal combustion the cycle’s character : two-stroke engine ( motorcycle) and four-stroke engine( cars, coaches, trucks) the way the combustion takes place: fast combustion (Otto) and slow combustion (Diesel)

EXPLORE students conclude with their description of the phenomena, expressing their concepts based on experiences. The main characteristics of heat engines – the students are stimulated to identify the heat engines characteristics based on their daily life knowledge. Example: 100km fuel consumption - the average quantity of fuel consumed to complete a distance of 100 km..

EXPLORE Students generate ideas, data, perception. How does a heat engine work? - It uses the heat resulted from the combustion of fuel. The components of the heat engine: cylinder, connecting rod, crank, combustion chamber, spark plug, and valve trains

EXPLORE Object and phenomena are explored Visit the Technical Museum “Dimitrie Leonida” - Bucharest

EXPLAIN: Strokes and processes in the running of heat engines Students explain their understanding of concepts and process New concepts and skills are introduced as conceptual clarity and cohesion are sought, Newly aquired concepts are summarized and generalized with teacher guidance Stroke’s nameThe description of the processes Comments Intake The fuel mix enters the cylinder. constant pressure process, Compression The intake valve train closes and the piston goes up producing the adiabatic compression of the work substance adiabatic compression Engine Stroke: Ignition, Combustion and Detent The piston reaches the superior end; the spark produced by the spark plug ignites the fuel mix which burns fast, causing the increase of temperature and pressure. The piston comes back in the cylinder. pressure raise at constant volume adiabatic rebound, Exhaust The piston reaches the course’s inferior end, the exhaust valve train opens, and the piston goes in the cylinder and exhausts the burnt gases pressure decrease at constant volume

Explain : Otto cycleDiesel cycle

Explain : the yield of heat engine OTTO yieldDIESEL yield

Elaborate : allows students to apply concepts in new context, and extend understanding and skills Strong points and weak points for each kind of engine Diesel engine Strong points It works with less fuel than a gasoline engine, performing the same work. The working time of a Diesel engine is two times longer than a gasoline one. The Diesel engine can also be used in mines, because it uses very little carbon monoxide. Not using electric power, the Diesel engine is more practical. Weak points It can cause cancer. Due to the high pressure, the engine can cause accidents. It produces polluting emissions.

Elaborate Similarities and differences between the Otto cycle and the Diesel cycle The Diesel engine : -can consume more types of fuel -produces more rotations (revolutions) in a shorter time -clean air is sucked in a cylinder, which is compressed more than in the case of Otto’s engine -works with a higher yield than the Otto -the combustion of the fuel is slower Differences: -The Diesel engine is more efficient than the Otto engine -In the case of the Diesel engine combustion of the fuel is slower -The Diesel engine works with a higher yield than the Otto -In the case of the Diesel engine clean air is sucked in the cylinder, which is compressed more than in the Otto’s case -The Diesel cycle has isochoric transformation, and the Otto has isobar transformation

Elaborate Similarities and differences between the Otto cycle and the Diesel cycle In the case of the Diesel engine, unlike the Otto engine, only clean air is sucked in the cylinder, which is compressed more than in the case of the Otto engine, this way the air reaches a temperature of 7000  C to 9000  C. The Otto engine sucks a gasoline and air mix, compresses it and ignites it using an electric spark. The Diesel engine sucks air, compresses air and then the diesel fuel, which ignites, is injected. The Otto engine uses a compression rate which varies between 8:1 and 12:1. The Diesel engine uses a lot higher compression rate, 14:1 to 25:1. The Otto engine uses a carburettor where gasoline is mixed with air, or an injection pump (the fuel is not injected directly in the cylinder). The Diesel engine uses direct injection, in which the fuel is injected directly in the cylinder.

Evaluate students assess their knowledge, skills and abilities students presentation Test y/proiecte/proiecte-motoare-termice/ y/proiecte/proiecte-motoare-termice/

This project has been funded with support from the European Commission. This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.