Arjan Helmantel

HCCI Operation of a Passenger Car Common Rail DI Diesel Engine With Early Injection of Conventional Diesel Fuel

The possibilities of operating a direct injection Diesel engine in HCCI combustion mode with early injection of conventional Diesel fuel were investigated. In order to properly phase the combustion process in the cycle and to prevent knock, the geometric compression ratio was reduced from 17.0:1 to 13.4:1 or 11.5:1. Further control of the phasing and combustion rate was achieved with high rates of cooled EGR. The engine used for the experiments was a single cylinder version of a modern passenger car type common rail engine with a displacement of 480 cc. An injector with a small included angle was used to prevent interaction of the spray and the cylinder liner. In order to create a homogeneous mixture, the fuel was injected by multiple short injections during the compression stroke. The low knock resistance of the Diesel fuel limited the operating conditions to low loads. Compared to conventional Diesel combustion, the NOx emissions were dramatically reduced. The smoke emissions also showed a significant reduction, while CO and HC emissions increased substantially. The HCCI combustion mode is characterized by a much more rapid heat release and higher fuel consumption, due to the lower compression ratio and the high HC and CO emissions.

Combustion and Emissions in a Light-Duty Diesel Engine Using Diesel-Water Emulsion and Diesel-Ethanol Blends

The purpose of the investigation presented here was to compare the effects of fuel composition on combustion parameters, emissions and fuel consumption in engine tests and simulations with five fuels: a diesel-water emulsion, a diesel-ethanol blend, a diesel-ethanol blend with EHN (cetane number improver), a Fischer-Tropsch diesel and an ultra-low sulfur content diesel. The engine used in the experiments was a light-duty, single-cylinder, direct injection, common rail diesel engine equipped with a cylinder head and piston from a Volvo NED5 engine. In tests with each fuel the engine was operated at two load points (3 bar IMEP and 10 bar IMEP), and a pilot-main fuel injection strategy was applied under both load conditions. Data were also obtained from 3-D CFD simulations, using the KIVA code, to compare to the experimental results and to further analyze the effects of water and ethanol on combustion. The experimental data indicated that the lower aromatic content of Fischer-Tropsch diesel fuel resulted in reduced soot emissions compared to conventional diesel. Use of Fischer-Tropsch diesel also gave lower NO\dx emissions. The diesel-ethanol blend gave a large reduction in soot emissions, but higher NO\dx emissions than the diesel-water emulsion. The lower heating value of the diesel-water emulsion resulted in increased fuel consumption in comparison to the diesel-ethanol blend and diesel. The addition of the cetane number improver (EHN) to the diesel-ethanol blend further reduced NO\dx emissions.

Injection Strategy Optimization for a Light Duty DI Diesel Engine in Medium Load Conditions with High EGR rates

Further restrictions on NOx emissions and the expansion of current driving cycles for passenger car emission regulations to higher load operation in the near future (such as the US06 supplement to the FTP-75 driving cycle) requires attention to low emission combustion concepts in medium to high load regimes. One possibility to reduce NOx emissions is to increase the EGR rate. The combustion-temperature reducing effects of high EGR rates can significantly reduce NO formation, to the point where engine-out NOx emissions approach zero levels. However, engine-out soot emissions typically increase at high EGR levels, due to the reduced soot oxidation rates at reduced combustion temperatures and oxygen concentrations. The work presented in this paper focuses on the optimization of a triple injection strategy to study the effect of injection timing, fuel mass distribution over the different injections and fuel rail pressure on emissions, combustion noise and fuel consumption for operation at medium load (10 bar IMEP and upwards) and high EGR rates (41%). The results of some of the test cases are compared with those obtained from modelling in KIVA-3V. By using an optimized triple injection strategy, soot emission levels could be reduced to below 0.04 g/kWh and NOx emissions to below 0.4 g/kWh at a medium engine load of 10 bar IMEP in a single cylinder research engine.

Operation of a DI Diesel Engine with Variable Effective Compression Ratio in HCCI and Conventional Diesel Mode

An experimental investigation was carried out in which an HSDI Common Rail Diesel engine was operated in both HCCI and conventional Diesel combustion modes, using conventional Diesel fuel in both cases. The engine used in the experiments was a single cylinder version of a modem passenger car engine with a displacement of 480 cc. In HCCI mode, the fuel was injected in multiple stages during the compression stroke, using a nozzle with a 60° included angle. To control the phasing and rate of combustion, the elective compression ratio was reduced by retarded intake valve closing. In addition, increased amounts of EGR were used. HCCI operation reduced soot and NO, emissions significantly. The use of a narrow included angle for conventional Diesel operation increased emissions significantly. The effect of a wider included angle and modifications to the piston were investigated experimentally and numerically. HCCI operation was also possible with a piezo injector with a 140° included angle. Because of the more accurate, shorter injections allowed by the piezo injector, interaction of the spray with the cylinder liner could be avoided, despite the wide included angle.

Visualization of the Effects of Post Injection and Swirl on the Combustion Process of a Passenger Car Common Rail DI Diesel Engine

The effects of variations in injection strategy and swirl on a DI Diesel engine performance and emissions were tested. The cylinder head was fitted with a small diameter endoscope, coupled with a triggered CCD camera, in order to study the effect of these variations on the combustion process. The images that were taken of the combustion process were used to calculate the spatial and temporal distribution of flame temperature and soot kks factor by using the 2-color method. The engine used in the experiments is a single cylinder version of a modern, passenger car type, common rail Diesel engine with a displacement of 480 cc. The fitted endoscope caused very little interference with the combustion chamber due to its small dimensions. The 65 degree angle view of the endoscope allowed coverage of a large portion of the entire combustion chamber. The combustion images and derived temperatures and soot concentrations were used to study the influence of post injection and high swirl. Adding a third (post) injection to the pilot and main injection increases the mixing and the flame temperature during the second half of the combustion process, thereby improving soot oxidation. The fuel efficiency was not negatively affected by the later phasing of part of the heat release. Increased swirl of the intake air was also studied. An 80% increase in swirl-ratio was achieved by closing off one of the two intake ports with a butterfly valve. The improved mixing gave significant reductions in soot emissions, with a small increase in NOx formation.Copyright

Reduction of NOx Emissions from a Light Duty DI Diesel Engine in Medium Load Conditions with High EGR Rates

The expansion of current driving cycles for emission regulations to higher load operation in the near future (such as the US06 supplement to the FTP-75 driving cycle) requires attention to low emission combustion concepts in medium to high load regimes. One possibility to reduce NO emissions is to increase the EGR rate. The combustion-temperature reducing effects of high EGR rates can significantly reduce NO formation, to the point where engine-out NOx emissions approach zero levels. However, engine-out soot and CO emissions typically increase at high EGR levels, due to the reduced soot and CO oxidation rates at reduced combustion temperatures and oxygen concentrations. The work presented in this paper focuses on different strategies to reduce soot and CO emissions associated with EGR rates of up to 50%, at which NO formation is largely avoided, but combustion temperatures are not low enough to consider the process as Low- Temperature Combustion (LTC). The studied strategies include use of high injection pressures (up to 1800 bar), increased swirl and increased boost pressures. Using a combination of these measures, soot emission levels could be reduced to 0.04 g/kWh and NOx emissions to 0.34 g/kWh at a medium engine load of 10 bar IMEP in a single cylinder research engine.