Strategies for emissions control in heavy-duty diesel engines to achieve low-emissions combustion with a high efficiency

Abstract

In this paper, the strategies for emission controls to achieve clean and high-efficiency combustion were studied in detail in a common-rail heavy-duty diesel engine coupled with exhaust gas recirculation. The results show that, in comparison with a single-stage turbocharger, a two-stage turbocharger dramatically improves the exhaust gas recirculation recyclability and enhances the air-to-fuel mass flow ratio. Therefore, nitrogen oxide emissions can be reduced to a much lower level, and the nitrogen oxide-brake specific fuel consumption trade-off relationship as well as the nitrogen oxide-soot trade-off relationship can be greatly improved simultaneously at low-speed high-load conditions. However, the peak cylinder pressure increases evidently at high-load conditions for a two-stage turbocharger. The brake specific fuel consumption, the soot emissions and the peak cylinder pressure can be lowered simultaneously by appropriately reducing the compression ratio and optimizing the geometry of the combustion chamber (such as the re-entrant diameter and the bowl depth) as well as using an injector with a tapered nozzle hole. At low-speed high-load conditions, the soot emissions can be reduced obviously without serious penalties in the brake specific fuel consumption when the nitrogen oxide emissions were kept constant by delaying the main-injection timing and reducing the injection pressure. However, it is necessary to employ a higher injection pressure together with a post-injection to reduce the brake specific fuel consumption and the soot emissions at high speeds. The combustion characteristics are mainly dominated by the cetane number of the fuel. With the addition of lower-cetane-number fuel to pure diesel, the ignition delay is prolonged as the exhaust gas recirculation rate increases, thereby also increasing the premixed combustion and reducing the soot emissions sharply. Meanwhile, the crank angle at which there is 50% completion of the accumulated heat release has less influence on the brake thermal efficiency with the addition of lower-cetane-number fuel. 2,5-dimethylfuran, as a novel oxygenated biofuel with a lower cetane number, is superior to gasoline for reducing the soot emissions, which may be a promising and clean alternative in compression ignition engines coupled with exhaust gas recirculation.

A characteristic study and optimization of in-cylinder configuration for particulate matters reduction in an off-highway diesel engine with mechanical fuel injection system

“…Chen et al studied the characteristics of the compression ratio and optimizing the geometry of the combustion chamber as well as using an injector with a tapered nozzle hole and performed the optimization of the parameters. 15 The results show that soot emissions are reduced without serious penalties in the brake-specific fuel consumption when the NOx emissions are kept constant by delaying the main-injection timing and reducing the injection pressure.…”

Numerical Investigation on Effects of Assigned EGR Stratification on a Heavy Duty Diesel Engine with Two-Stage Fuel Injection

“…In addition, fuel injection timing has an obvious influence on the combustion phase [34], which will influence in-cylinder temperature [35]. Hence the soot emissions can be reduced obviously without serious penalties in the brake-specific fuel consumption, while the nitrogen oxide emissions are kept constant by delaying the main-injection timing and reducing the injection pressure [36]. However, the demand for higher fuel economy and lower exhaust gas emissions from the compression ignition (CI) engine cannot be achieved by just using mechanically governed fuel injection systems [10].…”

Formation mechanism of static pressure circumferential double-peak distribution in a centrifugal compressor under the action of downstream boundary

“…Turbocharging can increase the density of the air absorbed by the internal combustion engine, thus increasing the power density, reducing fuel consumption and emissions of carbon oxides and nitrogen oxides. [1][2][3] It can also increase the limiting torque curve and torque back-up, and increase the engine rate. 3 Moreover, the size of the engine can be reduced by adding a turbocharger, which improves mechanical efficiency and reduces vehicle weight.…”