Diesel fuel efficiency takes shape with optimization

ISUZU Advanced Engineering Center (IAEC) enhances fuel efficiency by optimizing the combustion chamber design

In the debate on how best to tackle the impact of vehicles on environment, the improvement of diesel engine efficiency has emerged as a transitory but effective solution, especially for heavy-duty vehicles and passenger cars. Researchers at the ISUZU Advanced Engineering Center (IAEC) have analyzed how to enhance fuel efficiency by modifying the shape of the diesel engine combustion chamber.​


Figure 1: Calculated heat release rates and cylinder gas temperatures of re-entrant and shallow dish-type combustion chambers for an engine with a 115 mm bore and 125 mm stroke. [Courtesy of ISUZU Advanced Engineering Center​]

Theoretical thermal efficiency affects fuel consumption in diesel engines and one way of improving it is to increase the combustion chamber compression ratio. The resulting higher in-cylinder temperature and the expansion of the impingement area between fuel spray and chamber wall, however, can cause the chamber wall to heat up and lower theoretical efficiency. The team at IAEC looked at a new way of lowering heat loss by studying the combustion chamber shape, preventing the volumetric inefficiencies and cost and durability issues, which other methods caused.

 

modeFRONTIER helped us spot the optimal shape and further analyze the delicate trade-offs regarding the thermal balance.Keita Arato, Senior Research Engineer 1st Engine Research Development at IAEC


DidascaliaFigure 2: Degree of constant volume vs heat loss​​.
[Courtesy of ISUZU Advanced Engineering Center​]

To analyze the impact of the different chamber shapes, the team first defined the chamber outline and spray angle and adjusted it to match a given baseline compression ratio. The computational mesh was then created with CONVERGE CFD and modeFRONTIERwas used to pilot the 3D-CFD simulations. “In this way, we were able identify the shapes with the maximum cumulative heat release and work, and – at the same time - the minimum heat loss” says Keita Arato, Senior Research Engineer 1st Engine Research Development at IAEC.

 

 

 

 

 

 

“The shape with the highest cumulative rate of heat release was analyzed in depth. We compared it to calculated heat release rates and cylinder gas temperature profiles of re-entrant-type and shallow-dish-type chambers and, later, verified it using experimental data from a single-cylinder engine. The optimized chamber improved fuel consumption by 3.2% compared to its shallow dish-type counterpart. modeFRONTIER helped us spot the optimal shape and further analyze the delicate tradeoffs regarding the thermal balance” concluded Arato.