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Energy independence and reduction in pollutant emissions are a center of interest for several researchers and car manufacturers. Renewable fuels have gained in popularity because of their sustainability and, in some cases, lower amounts of greenhouse gases. Moreover, energy diversification is also required by all countries. One possible solution is the use of biofuels such as ethanol, methanol, etc. These biofuels have been shown as good candidates as alternative fuels for vehicles because they are liquid and they have several physical and combustion properties similar to gasoline. Alcohols have also a higher octane number and oxygen content than gasoline. This allows the alcohol engines to have much higher compression ratios (CRs), and thus, better BTE (brake thermal efficiency). Brazilian car manufacturing industry has developed flexible-fuel vehicles, introduced in 2003, which became a commercial success.

The power generation, used to promote comfort, mobility and others continually grows. The demand for energy grows as much as the number of studies in this field. To solve this growing demand, efforts have been directed towards the development of new energy sources, preferably renewable, and better ways of energy conversion by increasing the processes efficiencies. A good example of this is the gradual change from conventional and highly inefficient vehicles to hybrids or purely electric ones. But even with gradual migration for more efficient energy use, we will continue depending on traditional fuels. Therefore, it is necessary to develop more efficient and less polluting ways to use these sources. Thus, this work aims at studying alternative ways of converting energy contained in fuels used in internal combustion engines.

Gasoline is a volatile, inflammable mixture composed of olefinic, paraffinic, naphthenic and aromatic C4-12 hydrocarbons. Gasoline presents low contents of oxygenates and traces of sulfur, nitrogen and metals which introduce instability. In several countries, like Brazil, ethanol is used as an alternative fuel and as an octane improver. Nevertheless, hydrocarbons present in the fuel slowly react at room temperatures with atmospheric oxygen and with each other. This promotes changes in their physical-chemical characteristics. The process is observed throughout all the fuel production and use chain, increasing fuel density. These resinous, polymeric, insoluble and nonvolatile materials that are formed with high molar mass, commonly called gums, form deposits along the vehicle fuel system. Their accumulation can cause engine wear and have adverse effects on engine efficiency, performance and durability.

The period between the start of fuel injection into the combustion chamber and the start of combustion it's known as Ignition Delay (ID) or Delay Time. Delay period in the diesel engine exerts a very great influence on both engine design and performance. Functionally, the ID can be divided into two parts: the physical and chemical delay. The physical delay, it is the time between the beginning of injection and the attainment of chemical reaction conditions. During this period, the fuel is atomized, vaporized, mixed with air and raised to self-ignition temperature. Viscosity governs the physical delay of fuel combustion process, for low viscosity fuels, the physical delay tends to be small and vice versa. The chemical delay, during this period reactions start slowly and the accelerate until inflammation or ignitions takes place. Generally, chemical delay is larger than the physical delay.

In cars, optimizing their performance and improving their stability are of vital importance to manufacturers because of the highly competitive automotive market. These improvements could be achieved by developing analytical techniques for modeling the dynamic behavior of the car under certain conditions. They allow the vehicle to undergo various situations, which if were made with actual vehicles, would be expensive and require extreme or even impossible maneuvers. Certain dynamic parameters of the vehicle are required for them to model the real behavior of this system with an accurate precision. These parameters must be obtained from the real system by a data acquisition system or specialized tests.

Regarding fuels research and development, some preliminary studies - low cost and short time - can be conducted before the traditional engine tests - more expensive and time consuming. Therefore, experimental apparatus, such as a rapid compression machine (RCM) and specific methodologies, such as imaging techniques, are very useful in order to simulate engine combustion with simplicity, agility and flexibility, reducing development time and costs. Imaging techniques allow flame front propagation and ignition delay analysis, which are important parameters to understand fuel performance in engines and also to improve fuel modeling in engine simulation softwares. A RCM was adapted to operate in a spark ignition engine mode. It was used to obtain high-speed photos of flame propagation and ignition delay. Contour plots of the flame front profiles were obtained in successive frames to analyze the flame development with gasoline-ethanol blends.

Nowadays, many researches are being carried out to replace the diesel by alternative fuels. Biodiesel and ethanol are strong candidates for this purpose. However, the experimental study of the combustion of biofuels in engines is not an easy task. Due to the large differences between the properties of the new fuels and the conventional diesel, radical changes may be needed in current engines, developed specifically for the fossil fuel. So, the experimental study of ethanol compression ignition (CI) combustion is not simple to be obtained in conventional engines. Therefore, some experimental apparatus, such as a rapid compression machine (RCM), are useful to conduct this kind of study. This paper describes the RCM adaptations made in order to run CI combustion tests using Ethanol-Powered (ED95) and Diesel (S50) for different compression ratios and injection timing.

The development of a four-stroke engine, spark ignition, with direct injection of fuel into the combustion chamber was an important initiative for the global automotive market. The thermodynamic potential of this type of engine and its significant improvement in fuel economy have meant this technology as focus of a large number of research projects, with the objective to understand, develop and improve the system of direct fuel injection. However, to meet new emission limits set by Euro 5 specification, it was necessary to reevaluate the geometry design of the injector, which resulted in the development of a new component with a larger number of holes and with a diameter reduction (multi-holes injector). This change in the project aims to ensure a better spray, optimizing air / fuel ratio and, consequently, a better process of combustion inside the combustion chamber, satisfying the emission limits established by the applicable norms.

A four-cylinder turbocharged diesel engine was operated with natural gas and pilot diesel fuel ignition over a wide range of load and speed. The influences of different diesel-gas substitution ratios and air restrictions were evaluated regarding the characteristic parameters of combustion, performance and emissions. Based on data from the pressure-crank angle diagram, it was possible to evaluate some combustion characteristics such as the start of combustion, the maximum rate of pressure rise and the peak pressure. The parameters of the engine performance and emissions were analyzed through the brake specific fuel consumption (BSFC), unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOX). The results show that the increase of substitution ratio increase the maximum rate of pressure rise and the peak pressure at higher loads, but decrease at lower loads. With the air restriction, decrease the peak pressure.

Rapid Compression Machine (RCM) is an experimental tool developed to study combustion parameters. It allows to measure cylinder pressure and piston displacement as well as to film combustion through a transparent piston head. RCM is pneumatically and hydraulically driven device and it reproduces a single combustion shot, considering a compression and a partial expansion stroke. The RCM used in this work was originally manufactured for investigate the diesel engine combustion. This paper describes the RCM adaptations made in order to investigate the dual-fuel combustion characteristics of lean natural gas-air mixtures, using diesel fuel as ignition source. The RCM was equipped with high pressure common-rail diesel injection system and a compressed natural gas system. The natural gas and air were introduced in the combustion chamber, prior to compression stroke, and the pilot diesel fuel was adjusted to typical injection timing and durations of Diesel engines.