An innovative research on variable compression ratio in RCCI strategy on a power generator diesel engine using CNG-safflower biodiesel

Highlights: • Safflower biodiesel/CNG RCCI low temperature combustion was investigated. • Effects of different compression ratios were explored. • 3 novel parameters SPE, SHRE and STE were created to deeply analyze combustion. • The performance and combustion is more improved for biodiesel/CNG RCCI modes. • The lowest NOx and ultra-low smoke emissions were formed for biodiesel/CNG RCCI modes. The CNG usage as a fuel in IC engines have many advantages such as decreasing CO₂ and PM and smoke emissions and in many cases reducing NOx emission, along with its low prices and naturally abundance spread on the world. In heavy loaded operation of diesel engines, it becomes very hard to control excessive NOx, and PM formation in the exhaust emissions and smoke accumulation especially for biodiesel usage. In the present study, in order to achieve the usability of higher percentages of biodiesel with CNG, the low temperature combustion of reactivity controlled compression ignition (RCCI) strategy have been applied in a single cylinder diesel engine with variable compression ratios. The CNG, as the low reactivity fuel, was subjected to the intake manifold as the substitute the gas with 5%, 10% and 15% of biodiesel under 1500 rpm and 10.8 kW(full load) load of the engine with variable compression ratios from 13:1 to 19:1 in order to investigate the effects of compression ratios on RCCI operation with high percentages of biodiesel and CNG usage. Apart from the main performance, emissions and combustion indicators of diesel engines tests, 3 novel parameters (SPE, STE and SHRE) were created for the first time in order to deeply evaluate the combustion. Mean of cylinder pressure was increased while combustion duration was lowered for CNG usage with biodiesel. BTE was increased while BSEC and BSFC were decreased in either operation of biodiesel/CNG RCCI and various CR. In addition, NOx emissions were lowered for CNG usage and CR decrease, along with smoke decrease for biodiesel/CNG RCCI combustion.