**3.1 Premixed case**

### *3.1.1 In-cylinder pressure and heat release rate, Φ = 0.98*

For a mixture of 90% iso-octane (iC8H18) and 10% n-heptane (nC7H16) at ϕ = 0.98, numerical simulations were performed for comparison and validation are performed for in-cylinder pressure at the ignition timing of 20o BTDC. **Figure 3** shows the validation results showing a good agreement and prediction of in-cylinder pressure against the experimental data.

**Figure 4** shows a good agreement of predicted heat release rate (HRR) obtained from the numerical solution from the reduced mechanism using KIVA-CHEMKIN interface against the experimental data. HRR is the ratio of difference in heat release values and corresponding crank angle values. These values are obtained from KIVA output file. This also shows that detailed chemistry is very important to capture the correct trend of engine performance parameters. The reduced mechanism achieved from this research has given a confident deduction that the numerical simulations for ϕ = 0.98 has successfully modeled the engine performance parameters of in-cylinder pressure and heat release rate (HRR). It is recommended to build a library of reduced mechanisms for all the fuels that are used

*Numerical Simulations and Validation of Engine Performance Parameters Using Chemical… DOI: http://dx.doi.org/10.5772/intechopen.106536*

**Figure 3.** *In-cylinder pressure; 100,000, 178,000 & 230,000 cells.*

in the internal combustion engines so that the correct prediction of experimental results can be recorded and achieved.

### *3.1.2 In-cylinder pressure and heat release rate, Φ = 1.3*

Numerical simulations and comparison is performed below for a mixture of 90% isooctane (iC8H18) and 10% n-heptane (nC7H16) at ϕ = 1.3 using the reduced mechanism.

#### **Figure 4.**

*Heat release rate (HRR); 100,000 cells.*

Good prediction of in-cylinder pressure for ϕ = 1.3 is achieved using the reduced mechanism and is shown in **Figure 5**.

**Figure 6** shows the heat release rate (HRR) for ϕ = 1.3. The results for Heat release rate (HRR) obtained from the numerical solution from the reduced mechanism using KIVA-CHEMKIN interface again shows a good prediction. This also shows that detailed chemistry is very important to capture the correct trend of engine performance parameters.

#### *3.1.3 Emissions*

Apart from validating the engine performance parameters of in-cylinder pressure and heat release rate (HRR), this study also validated the emission results with the experimental data [21]. The engine-out exhaust emission data is shown in **Figure 7** for the exhaust species of H2, CO2 and CO. The results show a good agreement between the numerical and experimental results for the equivalence ratio of ϕ = 0.98 and ϕ = 1.3, where the predicted values of exhaust species of H2, CO2 and CO obtained through combustion-CFD simulations exactly match the experimental data at the equivalence ratio of ϕ = 0.98. At ϕ = 1.3, H2 and CO values obtained through

*Numerical Simulations and Validation of Engine Performance Parameters Using Chemical… DOI: http://dx.doi.org/10.5772/intechopen.106536*

**Figure 5.** *In-cylinder pressure; 100,000, 178,000 & 230,000 cells.*

numerical simulations exactly match and overlap the experimental value while CO2 values also show a good agreement. The results obtained from **Figure 7** shows that the reduced mechanism developed was able to validate the engine performance parameters as well as the emissions which makes this reduced model reliable in predicting performance parameters for premixed spark ignition engines.

#### **3.2 Direct-injection case**

Numerical simulations are performed for the direct-injection case at equivalence ratio of 1.0. The pentroof engine geometry and mesh is shown in **Figure 2** and specification are mentioned in **Table 3**. There are no moving valves in the geometry.

**Figure 6.** *Heat release rate (HRR); 100,000, 178,000 & 230,000 cells.*

*Numerical Simulations and Validation of Engine Performance Parameters Using Chemical… DOI: http://dx.doi.org/10.5772/intechopen.106536*

Results shown in **Figure 8** and **Table 4** represent the importance of using the detailed chemistry in the CFD solvers where detailed chemistry has improved and better predicted the engine performance parameters.

To test the effect of the breakup model, numerical simulations were performed for global mechanism, quasi-global mechanism and, reduced mechanism obtained

#### **Figure 8.**

*Maximum or peak in-cylinder pressure (breakup model on).*


**Table 4.**

*Maximum or peak in-cylinder pressure at stoichiometric conditions for direct-injection case.*


#### **Table 5.**

*Summary of results for breakup model analysis.*

through this research, with breakup model turned off. The global reaction mechanism still over predicted the results of in-cylinder pressure while the quasi-global mechanism under predicted the results. Summary of results is given in **Table 5**.
