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EN
Flammability limits and flame speeds of dilute-lean fuel mixtures of hydrogen (H2) and acetylem premixed with oxygen (02) and nitrogen (N2) were examined with a detailed kinetics model. These mixtures are used in a preburn in a constant volume combustion vessel to create elevated temperatures and pressures with gas compositions that represent the thermodynamic state in a diesel engine combustion chamber at fuel injection and auto ignition. A mixture of hydrogen and acetylene with combined atomic hydrogen to carbon ratio (HCR) of 1.85 was used to match that of typical diesel fuel and results are shown in comparison to a previously used mixture with a HCR of 1.17. The lower flammability limit (LFL) of the HCR 1.85 fuel mixture was found at an equivalence ratio of 0.235, while flame speed and adiabatic combustion temperatures were also predicted for post preburn product oxygen levels between O and 21 percent. Flame speeds were shown to decrease with a reduction in oxygen concentration, an increase in nitrogen dilution, while combustion temperatures increased over most of this range. Trends for this relation of flame speed and temperature are presented and a new premixed fuel mixture with an HCR of 1.85 is proposed.
EN
Combustion of lean hydrogen-air mixtures in an internal combustion (IC) spark ignited (SI) engine in respect of combustion knock effect is presented in this paper. It is known that making the combustible mixture leaner leads to both decreasing in-cylinder peak temperature of combustion and lengthening ignition lag. It also increases combustion duration. Having these issues on mind it could be concluded that combustion knock intensity decreases as well. It is reported that such a hypothesis is also correct when hydrogen based fuels are combusted in the IC engine, although hydrogen as an engine fuel, on the contrary to gasoline, is very susceptible to knock generation throughout the entire combustion duration. At the beginning the paper examines the combustion knock intensity on the basis of in-cylinder pressure traces. Next, a test-bed and obtained experimental results of hydrogen combustion in the IC single cylinder CFR engine are showed. Finally, analysis of knock intensity referring to lean hydrogen-air mixture ratio, expressed by the excess air number so-called lambda, is carried out. Significant conclusion from the analysis is that there is strong negative correlation between the hydrogen knock intensity and the excess air number lambda. In the end, comparison with exhaust gas recirculation as alternative way to reduce combustion knock, and constraints for leaning the hydrogen-air combustible mixture for the IC engine are discussed in the paper.
EN
In the US transportation sector uses two-thirds of the country's total oil consumption. In order to minimize the consumption in this sector there is a need to investigate alternate sources of energy. Biodiesel is a possible alternative to conventional diesel. Biodiesel has many characteristics similar to petroleum based diesel and can be blended with petroleum. However biodiesel's differences in fuel properties including viscosity, bulk modulus, density, and energy content can have significant impacts on engine performance parameters like BSFC and thermal efficiency. As the availability of biodiesel fuel increases, the need for engines capable of running on various mixtures of biodiesel fuel will be required. Similar to flex-fuel ethanol vehicles, control systems for the diesel engine and aftertreatment systems will need to detect and compensate for the fuel type. In this work, a soy based B100 biodiesel fuel and an ultra low sulfur diesel fuel were tested in a high-speed direct-injection high pressure common rail four-cylinder 1.9 L diesel engine. An internally developed engine control strategy allowed real-time calibration and testing of independent control parameters including start of injection, injection duration, injection pressure, and exhaust gas recirculation (EGR) level. Both the fuels were studied under varied injection timing (0°BTDC to 12°BTDC with increments of 3°) and EGR percentages of 0 and 10%. Analysis was performed to determine the Torque, BSFC and Brake thermal efficiency.
EN
Biofuels have the potential to diversify transportation energy sources and reduce dependence on petroleum based fuels. Of these biofuels, Methyl-ester biodiesel holds significant potential as it has many characteristics similar to petroleum based diesel and can be blended with petroleum. However, biodiesel's differences in viscosity, specific energy, oxygen content, and cetane number can cause significant changes in engine performance and emissions. Therefore, it is of prime interest to understand the combustion behaviour of biodiesel and identify key factors that contribute changes in engine performance and emissions. In this study, a 100% biodiesel fuel derived from soy and an ultra low sulphur diesel fuel were tested in a high-speed direct-injection high pressure common rail four-cylinder 1.9L diesel engine. The engine control strategy allowed real time calibration and testing of independent control parameters including start of injection, injection duration, injection pressure, and exhaust gas recirculation (EGR) level. The engine was equipped with in-cylinder pressure transducers for combustion analysis. Instrumentation for gaseous emissions detection and carbaceous particulate matter (PM) sampling was also utilized. Both the fuels were studied under varied injection timing of 0centigrade BTDC to 12 centigrade BTDC in increments of 3 centigrade, EGR percentages of 0 and 10%, and injection pressures of 400 to 900 bar. Analysis was performed to determine the rate of heat release, ignition delay, NOX and PM emissions.
EN
Combustion knock in a hydrogen fuelled engine has many different characteristic as compared to knock occurring in the gasoline engine. This is a result of differences in the gasoline and hydrogen combustion mechanisms which lead to knock. Hydrogen as the engine fuel is able to produce combustion knock of significant intensity. This intensity can be determined by measurements, which have been successfully applied for examining knock generated by the gasoline fuelled engine. This paper describes the engine test bed, in-cylinder pressure traces and methods for determining knock intensity. Further, the statistical approach for characterizing combustion knock is also presented. It concentrates on applications of several probability distributions for expressing individual knock intensity metrics of hydrogen port fuelled spark ignited engine. It is assumed that knock metrics for engine working cycles are considered as random variables. The knock metrics are based on the fluctuation component of the in-cylinder pressure traces sampled at 100 khz and are calculated for 300 consecutive engine working cycles. It was noticed that the knock metrics distribution profile changes as the knock intensity varies from light to heavy knock. In the paper, modelling of this knock distribution profile using several known stochastic distributions is also presented. Finally, usefulness of statistical distributions for characterizing combustion knock is shown.
EN
It is known that Exhaust Gas Recirculation (EGR) can be successfully applied not only for reducing NOx content in exhaust gases but also for reduction of combustion knock in SI engines. From this point of view, EGR can be particularly effective for knock elimination in the hydrogen reciprocating engine. Additionally with the application of EGR, the H2-air combustion can be maintained at the stoichiometric ratio enabling highly efficient NOx reduction in catalytic converters. In this paper a strategy of estimating EGR for the naturally aspirated, hydrogen fuelled engine is explained. On the basis of this strategy, the closed loop control system of the EGR was built and was implemented for the single cylinder CFR engine. There is also an outline of the test bed and several examples of in-cylinder pressure courses recorded under various EGR percentages. Next, the impact of EGR on combustion knock in the hydrogen fuelled engine is presented. Finally, conclusions concerning EGR application for hydrogen combustion in the IC engine are presented. EGR calculation and control scheme, main diagram of EGR calculation, subroutine (Sub-block) for calculating the molecular weight of EGR gases, in-cylinder pressure traces for several EGR levels during hydrogen combustion in the CFR engine, the fluctuating component of in-cylinder pressure during hydrogen combustion with several levels of EGR, peak pressure of fluctuation component of in-cylinder pressure vs. EGR percentage are presented in the paper.
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