Fuel injection and combustion study by the combination of mass flow rate and heat release rate with single and multiple injection strategies

• The fuel mass flow rates were measured with long tube measuring system to reveal the actual shape of fuel injection rate.
• Various injection strategies were characterized by the profiles of mass flow rate.
• The dominant factors for interaction and the influences of interaction on injection characteristics were investigated.
• Through the combination of mass flow rate and heat release rate information, the combustion characteristics were studied.

The injection and combustion characteristics are complicated when split injection strategy is used due to strong interaction between splits. Various injection tests were carried out with long tube real-time fuel flow measuring instrument by employing both single and split injection strategies. Many engine tests with selected operation points (various pilot injection quantities, various injection dwells and various numbers of split injections) were also carried out with split injection strategy, enabling the combination of mass flow rate (MFR) and heat release rate (HRR) information to study combustion features. The results showed that raised injection pressure shortened the injection delay and increased the MFR. The actual injection duration was much longer than the TTL duration. More importantly, for multiple injections, the interaction between splits was dominated by the duration of the first split and injection intervals. The number of splits also exerted profound influence on the interaction. In addition, higher MFR for pilot injection near the piston TDC adversely affected the HRR and normalized combustion efficiency. Increased split injections with low MFR can effectively lower the peak HRR thus reducing the maximum temperature and NOx emissions.