An Experimental Study on Combustion and Performance of a Liquefied Natural Gas–Diesel Dual-Fuel Engine With Different Pilot Diesel Quantities

The pilot diesel quantity (m_pilot) has an impact on the liqueified nitrogen gas (LNG)-diesel dual-fuel engine, but it is very difficult for a dual-fuel engine with the traditional injection system to adjust m_pilot to meet various operating conditions in practice. In recent years, with great progress in common rail diesel injection technology, m_pilot can be adjusted accurately by the electronic control system, which is an advantage for operation with the diesel–LNG dual-fuel. In order to optimize m_pilot of the diesel–LNG dual-fuel engine, the combustion and performance of a dual-fuel engine with the m_pilot of 5.05 mg/cyc, 5.20 mg/cyc, 5.69 mg/cyc, 6.31 mg/cyc and 6.91 mg/cyc under 50% load at speed of 1600 r/min were analyzed. Experimental results show that, with an increase in m_pilot, the maximum in-cylinder pressure, rate of pressure rise, and heat release rate of dual-fuel obviously increase, the crank angles of the maximum value move forward, and the combustion duration becomes shorter. The mean value of peak in-cylinder pressure (p_max) increases obviously while the standard deviation of it decreases, and the distribution of that focuses. The mean value of the crank angle corresponding to p_max pressure decreases except for the m_pilot of 5.05 mg/cyc, while the standard deviation of that gradually decreases, the distribution of it focuses and moves forward. The brake power increases while the brake-specific fuel consumption (BSFC) decreases, the CO and HC decrease, while the CO₂, NO_x, and smoke density emissions increase.