Evaluation of the Air Oxygen Enrichment Effects on Combustion and Emissions of Natural Gas/Diesel Dual-Fuel Engines at Various Loads and Pilot Fuel Quantities

Abstract

The use of natural gas (NG) as supplement of the normal diesel fuel in compression ignition (CI) environments (Natural Gas/Diesel Dual-Fuel, NG/DDF), seems to present an answer towards reducing soot or particulate matter (PM) and nitrogen oxides (NOx) emissions in existing and future diesel engine vehicles. The benefits for the environment can be even higher, as recently NG quality gas can be produced from biomass (bio-methane or bio-CNG or ‘green gas’). However, this engine type where the main fuel is the gaseous one and the diesel liquid fuel constitutes the ignition source (pilot), experiences higher specific energy consumption (SEC), carbon monoxide (CO), and unburned hydrocarbons (HC) emissions compared to the conventional (normal) diesel one, with these adverse effects becoming more apparent under partial load operation conditions. Apart from using bio-fuels as pilot fuel, it is anticipated that air oxygen enrichment—addition of oxygen in the intake air—can mitigate (at least partly) the associated negative results, by accelerating the burning rate and reducing the ignition delay. Therefore, the present work strives to investigate the effects of various degrees of oxygen enrichment on the combustion, performance, and emissions of such a NG/DDF engine, operated under various loads and pilot (diesel fuel) quantities. The study is carried out by using an in-house, comprehensive, computational model, which is a two-zone (phenomenological) one. The accuracy of the modeling results are tested by using related experimental data from the literature, acquired in an experimental investigation conducted on a naturally aspirated, light-duty, NG/DDF engine. The computational study is extended to include various pilot fuel quantities, attempting to identify the influence of the examined parameters and witness advantages and disadvantages. The study results demonstrate that the air oxygen enrichment reduces the specific energy consumption and CO emissions, by accelerating the burning rate and reducing the ignition delay (as revealed by the cylinder pressure and rate of heat release diagrams), without impairing seriously the soot and NO emissions. The conclusions of the specific investigation are much useful, particularly if wished to identify the optimum combination of the parameters under examination for improving the overall performance of existing CI engines functioning under natural gas/diesel fuel operating mode.

An Investigation of the Influence of Gas Injection Rate Shape on High-Pressure Direct-Injection Natural Gas Marine Engines

“…It is critical to include AMR to capture important flow features without requiring unrealistically large cell counts. As mentioned before, nowadays, natural gas can be produced from various biomass feedstocks [15,16]; moreover, the process of converting biogas into biomethane can be industrialized [45]. Whether it is biomethane or natural gas from fossil energy, its main component is methane [15,16,45,46].…”

“…In addition, the high-octane value and antiknock properties permit a high compress ratio, therefore achieving high thermal efficiency [13,14]. Moreover and more importantly, nowadays, natural gas can be produced from various biomass feedstocks [15,16], thus increasing its eco-friendly merits, with this gas called bio-methane, bio-compressed natural gas (CNG), or "green gas". Previous studies showed that natural gas engines could reduce NOx emissions by approximately 50-80% while producing almost zero soot emissions [17].…”

Study of the Effects of Biofuel-Oxygen of Various Origins on a CRDI Diesel Engine Combustion and Emissions

“…Secondly, due to lower stoichiometric air/fuel ratio less fresh airborne oxygen will be consumed to burn the fuel completely, which certainly contributes to a better ambient air quality in densely populated metropolitan cities. These beneficial features of ethanol in a company with its well-known cooling effect can be utilized in practice bearing in mind that the NO x formation relies (primary) on the in-cylinder temperature, local oxygen concentration, the residence time limited by the combustion reactions, and relative (overall) air/fuel ratio [82], but depends less on the availability of the local oxygen [18]. As a result, using of the fuels oxygenated with ethanol has the potential to reduce the amount of time needed for clean combustion and to a certain degree of improvement contribute to production of less nitric oxides (NO) when running under the most common loading conditions.…”

“…The extended studies on the alternative fuels such as shale oil [14][15][16], KDV synthetic diesel fuel [17], natural gas/diesel, and diesel dual fuels [18] have been recently conducted to improve engine efficiency, reduce noise, exhaust smoke, and pollutant emissions. The theoretical and practical issues associated with the development, production, and the test results of turbocharged auto-tractor Diesel engines and their fuel systems with the high-pressure, electro-hydraulically controlled injectors to efficiently operate on alternative fuels such as dimethyl ester (DME) and a natural gas presents Reference [19].…”

“…The research on biodiesel blends with a naval aviation turbine fuel JP-5 and biodiesel [34], biofuels derived from sustainable sources blended with civil aviation kerosene Jet A-1 [35], aviation turbine JP-8 fuel blended with sunflower methyl ester [36] or rapeseed biodiesel [37], as well as toxic components emitted by a marine engine [38,39] have also been provided over the recent decades to reduce ambient air pollution. As the current study intends to examine the fuel-oxygen of various origins and enrichment rates effects on the combustion process, maximum heat release rate, in-cylinder pressure, its cyclic variations in tandem with the IMEP developed, and exhaust emissions, the investigations related with variation of the air-oxygen [18] and/or the fuel-oxygen [40] enrichment rate made effects on the engine performance mentioned above are of a special importance.…”