Optimization of BSFC and NOx emission of 4 cylinder diesel engine using GT suite
Objective:
1. To model 4 cylinder diesel engine with DI pulse(predictive) combustion model
2. To Study the effect of Start of ignition(SOI) and rail pressure on BSFC and NOx emission. Also to optimize BSFC and NOx emission by considering SOI and rail pressure as parameters.
Optimization:
Optimization is the selection of a best element (with regard to some criterion) from some set of available alternatives.In the simplest case, an optimization problem consists of maximizing or minimizing a real function by systematically choosing input values from within an allowed set and computing the value of the function.
Model:
The above model is turbocharged (VGT) 4 cylinder direct injected diesel engine. EGR is also used to control the in cylinder temperature and NOx emission. Predictive combustion model DI pulse is used in this model in which the burn rate is predicted from various parameters.
Optimizer:
The primary objective is to optimize i.e. minimize brake specific fuel consumption(BSFC) and NOx in ppm by considering the variation in Start of injection(SOI) and Rail pressure. Integrated design optimizer is used since multi objective. Generic alogrithmn is implimented. Genetic Algorithm is an evoluationary, global search algorithm, specifically NSGA-III. It is recommended for all problems having medium to high complexity, which would result from many factors, the presence of one or more constraints, and non-linear characteristics. The lower limit and upper limit of start of ignition is set as -10 and 5 degrees and rail pressure is set as 1500 and 2000 bar. In responses bsfc and NO(ppm) is set to minimize as objective.
Case setup:
In case setup, rail pressure and start of ignition is set as parameter and given initial value of 1600 and 0 respectively. engine rpm is 4000 rpm and target bmep is 16.
Results:
1. Effect of SOI on BSFC
From above plot we can observe that as delay in start of ignition results in increase in bsfc.Therefore early SOI is necessary in order to maintain lower bsfc.
2. Effect of rail pressure on bsfc:
From above plot we can observe that, single optimal point for lower bsfc is not available in case of rail pressure due to presence other important factors. Optimal case for bsfc can be selected by selecting suitable operating condition.
3. Effect of SOI on NOx emission:
From above plot we can observe that, the earlier fuel is injected higher amount of NOx is produced, Therefore start of ingnition should be delayed in order to reduce incylinder temperature thereby NOx emission.
4. effect of rail pressure on NOx emission:
from above plot we can observe that a single optimal point is not present and cases can be considered depending on other operating points. In general NOx emission is least at lower rail pressure.
5. BSFC vs NOx emission:
From above plot we can observe that, if we aim for minimal bsfc results in higher NOx emission. Similarly if we aim for minimal NOx then higher bsfc will be obtained. Therefore we can say these outputs are inversly proportional. Some amount of comprimise is necessary and optimal case can be selected by considering the necessity of the consumer of the product. For example if consumers of product expect lesser bsfc then case can be selected suitably and if consumers prefer lesser NOx emission then other case can be selected.
6. Sensitivity comparison for Responses vs Factors
In our case, factors are SOI and rail pressure. Responses are bsfc and NOx emission.
From above plot we can observe that, both SOI and rail pressure have almost equal sensitivity on bsfc and NOx emission. But SOI has higher sensitivity for NOx emission than bsfc comparatively and rail pressure has higher sensitivity for bsfc than NOx emission comparatively. Comparing the relative sensitivity of SOI and rail pressure, we can observe that SOI has 0.75 and rail pressure has 0.25 comparativly.Therefore we can conclude that SOI is more sensitive than rail pressure in case of minimizing BSFC and NOx emission.
Conclusions:
1. SOI and rail pressure have almost equal sensitivity on bsfc and NOx emission. But SOI has higher sensitivity for NOx emission than bsfc comparatively and rail pressure has higher sensitivity for bsfc than NOx emission comparatively. Comparing the relative sensitivity of SOI and rail pressure, we can observe that SOI has 0.75 and rail pressure has 0.25 comparativly.Therefore we can conclude that SOI is more sensitive than rail pressure in case of minimizing BSFC and NOx emission.
2. if we aim for minimal bsfc results in higher NOx emission. Similarly if we aim for minimal NOx then higher bsfc will be obtained. Therefore we can say these outputs are inversly proportional. Some amount of comprimise is necessary and optimal case can be selected by considering the necessity of the consumer of the product. For example if consumers of product expect lesser bsfc then case can be selected suitably and if consumers prefer lesser NOx emission then other case can be selected.
3. the earlier fuel is injected higher amount of NOx is produced, Therefore start of ingnition should be delayed in order to reduce incylinder temperature thereby NOx emission.
4. Delay in start of ignition results in increase in bsfc.Therefore early SOI is necessary in order to maintain lower bsfc.