# Application of Canola Oil Biodiesel/Diesel Blends in a Common Rail Diesel Engine
## 3 Results and Discussion  
### Combustion Characteristics  
#### 3.1.1 Combustion Pressure and Rate of Heat Release (ROHR)  
Combustion characteristic analysis is an important index to measure engine performance. In general, the combustion characteristic is analyzed by using cylinder gas pressure, rate of heat release, ignition delay period, combustion durations, coefficient of variation in indicated mean effective pressure, and brake specific fuel consumption. Figure 3 shows the effects of ULSD, BD20, and PCO on the combustion pressure and ROHR at various brake mean effective pressures. At 0.13 MPa, 0.26 MPa, 0.39 MPa, and 0.52 MPa, the PCO's combustion pressure decreases 43.5%, 28.6%, 12.6%, and 8.4% compared with ULSD, respectively. In addition, as shown in Figure 3a,b, the combustion pressure decreased successively with the proportion of canola oil in the blends is increased. At 0.26 MPa, the combustion pressures of three kinds of test fuels were closer than that of at 0.13 MPa. It can  
Figure 2: Stages of combustion in compression ignition (CI) engines. be explained that the high density and viscosity of PCO, compared to ULSD, leads to PCO's less easy atomization at low BMEP (0.13 MPa). Increasing the value of BMEP has the effect of improving atomization and fuel burning. Another reason is that the lower calorific value of PCO is lower than that of ULSD and BD20 (see Table 1). These similar results were also observed by other researchers [41; 43]. However, as shown in Figure 3d,c, it can be observed that the combustion pressure of BD20 is the highest, and the three kinds of test fuels' combustion pressures are very similar. It can be noted from the Table 1 that BD20 is an oxygenated fuel and can be burned more completely with a higher oxygen concentration at middle and high engine loads (0.39 MPa and 0.52 MPa). Although the PCO is the highest oxygenated fuel, high density and high viscosity are its main disadvantage (at about 1.5 times that of ULSD; see Table 1). For the ROHR of three kinds of test fuels, as shown in Figure 3, the peak value of the ROHR occurred at crank angles over 0\({}^{\circ}\), which is an inherent characteristic of a diesel engine's ignition delay. In addition, from Figure 3a-d, it can be clearly observed that the ignition delay periods of BD20 and PCO are faster by about 3\({}^{\circ}\) and 5\({}^{\circ}\) of crank angle (CA), respectively, compared with ULSD. It can be explained that the cetane number (61.5) of PCO and viscosity (4.29) is higher than that of ULSD (see Table 1), and it leads to the compressibility of PCO fuel being lower and the combustion of PCO fuel starting faster than that of ULSD [41; 43]. At middle and high engine loads (0.39 MPa and 0.52 MPa), the ROHR of BD20 is the biggest compared with ULSD and PCO, it is again verified that the influence of the oxygen content is great [43; 44]. In order to comprehensively investigate the application of canola oil in a common rail diesel engine, the combustion pressure and ROHR for each test fuel are shown in Figure 4. For each kind of fuel, the combustion pressure increased clearly with increasing BMEP. At high engine load (0.52 MPa), the combustion pressure of ULSD, BD20, and PCO increase 34.6%, 47.1%, and 72.4% compared with  
Figure 3: Effect of test fuels on combustion pressure and ROHR (Rate of Heat Release) at various BMEPs (brake mean effective pressures). (**a**) 0.13 MPa; (**b**) 0.26 MPa; (**c**) 0.39 MPa; (**d**) 0.52 MPa. that of at low engine load (0.13 MPa), respectively. In particular, for BD20 and PCO, this combustion pressure increased effect is very significant. This because the BD20 and PCO are high density and high viscosity fuels, they can be burned fully at high engine loads. With increasing BMEP, the injection pressure of the fuel and the turbulence intensity in the combustion chamber increased, which built a better atomization environment.