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Kubota V1505T - Smallest Cylinder Bore Common Rail Engine

EU Stage V regulations are highly strict on emissions. In order to meet customer needs and enhance its leading position on the European market for small compact diesel engines, Kubota has developed the V1505T common rail engine and achieved DI combustion with the smallest cylinder bore, realizing a compactness comparable to a competitor's 3-cylinder engine.

Kubota V1505T is a 4-cylinder, 1.498 l, 33 kW diesel engine of 78 mm bore. To comply with the emission regulations in the output category of 19 to 37 kW, the company developed the engine with the adoption of Common Rail System (CRS), DPF, and EGR devices. In order to adopt CRS, the combustion system needed to be changed from IDI to DI. The challenge - there is no Common Rail engine of such small bore diameter as the basic V1505T model.

In addition, the volume of the main combustion chamber of a piston is also the smallest in the industry. Thus, the time until the fuel spray reaches the wall of the combustion chamber is very short compared with the upper class series where the bore diameter is large. Fuel spray is coarsened when it interferes with the wall and does not contribute to combustion. Consequently, it causes a worsened fuel consumption cost and emission gas performance.

The solution to this challenge is a four-valve CDIS (Center Direct Injection System). It features injectors which are vertically located with the centre focused on the cylinder bore. This modification contributed to the equalization of fuel spray into the cylinder and improvement in the mixture with air. By adopting two intake and two exhaust valves the swirl flow (rotational flow around the cylinder centre) was strengthened to optimize the air flow. The engineers also modified the shape of the combustion chamber.

Finally, combustion satisfying the Stage V emission performance was achieved by the introducing of four-valve CDIS and the optimization of the combustion chamber and fuel injection angle. Also, the Common Rail engine of the smallest cylinder bore diameter in the industry has a lower fuel consumption, which was reduced from the base model by 11%, and the product competitiveness was enhanced.



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