Development of a ram-swirled helical air intake device for a compression-ignition engine

Compression-ignition CI engines are highly efficient power devices compared to Spark Ignition SI engines and currently play a significant role in the transportation and industrial sectors. However, the engine has constraints with low engine performance, high fuel consumption and emissions levels which require continuous improvement. There are various designs of air intake systems to meet a certain engine operating range, still, there will be less actual amount of fresh charge entering the cylinder compared to the theoretical value due to the short cycle time available. This results in poor mixing of fuel-air mixture, increasing the incomplete combustion and amount of unburned fuel. The volumetric efficiency is also affected by the lower amount of intake air charged which contributed to the performance constraint. The study analyses the effect of the swirling airflow in CI engines on combustion behaviour, emissions and performance experimentally. The swirling air is generated by a novel design of ram-swirled air intake device studied with various parameters. The parameters include helical blade, cutting angle and cylinder draft angle. To come out with the final design, a simulation is conducted in Ansys Fluent software to identify the output flow direction and swirl strength based on the base model. A parametric study is further conducted by simulation to verify the output flow characteristics by changing the model’s aspect ratio. The experiment for the 3D-printed device is done on a single-cylinder, four-stroke, direct injection diesel engine connected to an eddy current dynamometer. The result shows that the addition of the basic design of the swirl air intake device increases the engine performance at full load with the brake power and torque increase by 2.9% to 5.3% at various engine speeds. The emissions levels are also improved with a significant drop by 34.6% to 55.3% in the NOx, UHC and CO levels. The device has shown the ability to enhance the air-fuel mixing in the combustion chamber based on the in-cylinder pressure, where the SOC event starts earlier for shorter ignition delay as a result of better homogenous mixing. Experimental results of the parametric study show a consistent, good agreement and better performance with further increase in the brake power and torque by up to 5.8% to 18.4% at various engine speeds. These results conclude that the swirl air intake devices are capable of increasing the overall performance of the CI engine. This includes the improvement to the BSFC, BTE and exhaust emissions level which highly contributed by the enhancement of fuel-air mixing homogeneity.

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