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Since its invention, the automobile mostly works with a thermal internal combustion engine, 4-stroke, which can be fueled with petrol (spark ignition engines) and diesel (diesel engine).
Significant technological advances have increased the performance of these conventional engines to achieve energy savings.
The ecological concern is, too, in the heart of the search engine development.
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A conventional automobile engine generally consists of several combustion chambers. Each of them is delimited by the cylinder head, the cylinder and the piston. The engine architecture is also based on a kinematic connecting rod – crank that turns a reciprocating (piston movement) into rotary motion (rotation of the crankshaft).
The combustion of the fuel mixture (air-fuel mixture) in the room is reflected in every cycle by gas pressure rising which makes it possible to move the piston and connecting rod-crank system. The crankshaft is then connected to the mechanical transmission elements (gearboxes, drive shafts, etc.) for driving the vehicle wheels. The gearbox adapts the speed of the wheels to the engine.
Firstly, the performance of a motor depends on the amount of energy released by the combustion, therefore the amount of fuel mixture present in the combustion chamber. These are directly related to the volume of the room (per cylinder) and the number of rooms or engine cylinders (total displacement).
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These are the 4 time required for the cycle of transformation of chemical energy contained in the fuel into mechanical energy. Each time corresponds to a turn of crankshaft rotation (a climb or descent of the piston).
Beats 1 and 4 are time spent on gas transfer (intake of fresh gas and exhaust flue gas), times 2 and 3 are the necessary time to the preparation and implementation of combustion and its transformation into energy mechanical.
– 1st time: Admission (cylinder filling) – the piston moves down and sucks the air-fuel mixture.
– 2nd time: Compression – The piston rises compressing the air-fuel mixture; a spark is generated to ignite the mixture.
– 3rd time: Combustion – Relaxation It is that which corresponds to the development of combustion and expansion of the burnt gases: the piston is pushed down; the chemical energy is converted into mechanical energy.
– 4th time: Exhaust (Drain flue gas cylinder) the piston rises and discharges the exhaust gases.
– 1st difference: It’s the fresh air that is compressed and admitted at time 1 and 2, and the fuel is introduced directly into the cylinder (injection) at the end of compression.
– Second difference: The mixture ignites spontaneously, without spark due to the rise in air temperature due to its compression.
Cetane number characterizes the ability of diesel fuel to self-ignite spontaneously. The octane number characterizes the ability of gasoline to resist self-ignition in order to preserve uncontrolled combustions by the electric spark (abnormal combustions, knocking).
To achieve complete combustion of 1 g of conventional fuel (gasoline or diesel), it must, in theory, about 14.6 grams of air. The ideal mixture is called stoichiometric mixture.
– The current gasoline engines operate mostly in the stoichiometry. After introduction of a homogeneous mixture of air and fuel into the engine combustion (inflammation of the mixture) is initiated by a spark (ignition). The combustion results in the propagation of a flame front which sweeps the entire room.
– Diesel engines operate with excess air. Diesel fuel is injected under pressure into a mass of air previously compressed. The combustion is initiated by self-ignition (compression ignition). Combustion is said stratified or heterogeneous because it takes place in a medium consisting of both very fuel-rich zones (mostly located near the injector nozzle) and very poor areas, even without fuel (near the cylinder wall).
The engine is a chemical energy into mechanical energy transformer. The efficiency of a motor is the ratio of the power supplied to the motor (chemical energy contained in the fuel) and mechanical energy returned. It is important to optimize this performance to prevent energy loss, particularly in a context of sustainable development.
Under optimum operating conditions, a car engine today offers a maximum return of around 36% for a petrol engine and 42% for a diesel engine. That is to say that, on average, just over a third of the energy supplied by the fuel is converted into useful energy to move the vehicle, with the remainder mainly dissipated in heat in the atmosphere. These optimal conditions however correspond to a high-load engine operation.
The maximum power required from the motor is determined by the mass of the vehicle, its maximum speed and its authorization of use (fight against the inertia related to the weight, advancement in the air resistance, acceleration potential).
However, in general, motor vehicles are used for short journeys in agglomeration, which finally results in a biasing of the engines at low loads. In these conditions, the yield is degraded, with values reaching 15%.
Great efforts in research and development are undertaken in this area in order to improve motor performance in all vehicle operating conditions. One of the ways of improvement is based on the concept of eco-boost (or downsizing).
This is to reduce the engine displacement (thus its size and weight), maintaining an equivalent level of performance to an engine larger displacement by supercharging technology (turbocharger). This process can substantially reduce energy loss from the engine.
This is primarily carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxide (NOx) and particulate matter in the diesel engines. Carbon dioxide (CO 2) is not regulated in terms of transport but is the subject of a commitment objective of reducing the share of European manufacturers.
This is the step of transforming the exhaust gas between the engine and the muffler, for cleaner emissions.
The after-treatment diesel and gasoline engines have therefore some differences. Currently, there are two main ways to make the post-treatment of emissions:
– The catalytic converter which converts mainly CO, HC and NOx, and that allows also reducing the soot particles (soluble organic fraction present on the particles),
– The particle filter (diesel only) which stores particles then burns them periodically (about 500 km) under strictly controlled conditions.
New technologies are being developed to further improve the treatment of emissions, among which we can mention, nitrogen oxide traps and catalysis “SCR” (with injection of a specific reducing agent, urea).
This is upstream processes, the treatment being carried out at the source in the combustion chamber. Two approaches are possible:
– Optimization of traditional combustion through the implementation of new technologies (injection, turbocharging, etc.)
– Implementation of new homogeneous combustion modes (see “developments of conventional engines and fuels”).
My name is Leroy L.Simmons. I create this blog as the way to find out my excitement and also a way to remember my father. I always love writing, I embarked on this adventure of the blog, to tell you all that I want to share about my hobby, my dream of auto, truck and journey. At MRVEHICLE.NET, I hope to tell you great stories and especially to answer some questions you might ask. And there are also many interesting and up-to-date stories of drivers on their journey everywhere in the world.
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