**1. Introduction**

Constructors of gasoline engines are faced with higher and higher requirements as regards to ecological issues and an increase in engine efficiency at a simultaneous decrease in fuel consumption. Satisfaction of these requirements is possible owing to the recognition of the phenomena occurring inside the engine cylinder, the choice of suitable optimal parameters of the fuel injection process, and the determination of the geometrical shapes of the combus‐ tion chamber and the piston head. All these parameters indeed have a considerable impact on the improvement of gasoline engines performance, and they increase their efficiency.

The increase in the engine efficiency is basically the result of the change in the fuel supply method, that is by proper regulation of the petrol-air mixture composition depending on the rotational speed and load. This is why the lean mixture combustion in the gasoline engine. Further lowering of the temperature during the development of the fuel-air mixture, which is an outcome of the heat being taken away from the evaporated spout by the surrounding air, makes it possible to increase the compression ratio, which translates to the increase of the ideal efficiency.

With direct petrol injection system, is essential for increasing the efficiency at a simultane‐ ous decrease of the toxic fumes emission and fuel consumption.

The first construction of the fuel supply system with electronically controlled direct injection system was introduced into batch production in 1996 by the Japanese Mitsubishi concern, in the Carisma model with the 4G93 GDI engine. The innovative solution made the disposed power and maximal moment grow by 10%, and the elementary fuel consumption fell by 20% in relation to the formerly used engine with indirect fuel injection system.

The improvement of the above mentioned parameters was possible owing to the implemen‐ tation of the system of laminar lean fuel-air mixture combustion in the range of partial load and low to medium rotational speeds of the engine. The laminar load was created by the wall-guided fuel injection.

An adequate gap between the injector and the ignition plug is necessary to accelerate the evaporation and diffusion of the sprayed fuel in order to make the too rich mixtures leaner around the ignition plug (λ < 0.5) which may delay the ignition. In accordance with it, the beginning initiation of injection should occur earlier and earlier with the increase in the rota‐

Stratified Charge Combustion in a Spark-Ignition Engine With Direct Injection System

http://dx.doi.org/10.5772/53971

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As a result, the point the fuel impinges the concavity in the piston differs at different velocities. The geometry of the concavity and the angle of injection were designed so that the behav‐ iour of the fuel after injection would not be sensitive to the moment and place of injection.

**2.2. Thermodynamics method of comparative cycle on the basis of heat amount**

**1.** Semi prefect gas is the thermodynamic factor performing the work in the cycle.

of the mass of the factor due to leakage of the cylinder equals zero.

**2.** The amount of the factor participating in the cycle is constant; which means that losses

tional speed.

γ - angle of injector position

**introduced into the cycle**

**Figure 1.** Variation of fuel mixture in combustion chamber.

The following assumptions were adopted for calculations:

**3.** Processes of compression and expansion are polytropic.

The injected fuel spout, with the proper angle of the crankshaft revolution during the com‐ pression stroke rebounces from the piston head and is directed towards the spark plug elec‐ trodes. The rapid development of internal combustion engines with direct petrol injection caused the introduction into batch production of the Renault concern IDE engines, Toyota's D4, Volkswagen group's FSI, PSA group's HPI, Ford's SCI, Mercedes' CGI, and the JTS unit used by Alfa Romeo.

In 2004 the first turbocharged engines with indirect petrol injection were introduced in Audi vehicles, and in 2006 Mercedes presented CLS 350 CGI model, in the engine of which the laminar load is created by the spray-guided injection. At present piezoelectric injectors are used in most direct injection systems, which characterize with considerably larger fuel dos‐ age accuracy than the hitherto used electromagnetic injectors. This type of fuel supply sys‐ tem shows that the gasoline engine with direct petrol injection, apart from the benefits resulting from the combustion of lean mixtures, has numerous other virtues, compared to the conventional fuel supply systems, namely:


The aim of engine constructors is essentially to increase the overall efficiency, not merely one of the partial efficiencies of which it constitutes, therefore the profound analysis of the above mentioned factors deciding of its real value is understandable.
