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The Partially Pre-mixed Charge Compression Ignition (PCCI) combustion was experimentally and computationally investigated with retarded injection timing for mixture homogeneity and for lower emissions. PCCI combustion concept was experimentally evaluated with retarded injection timing close to TDC with high EGR levels up to 50%. The CFD analysis has carried out for mixture homogeneity with different injection pressures and timings. A 4-cylinder TCIC engine having 2valves/cylinder were selected for experiments and speed vs. torque mapped for LCV applications. A Visio technique has been used to study the in-cylinder combustion. After fine tuning of injection pressure, injection timing and EGR ratio over entire range of engine speeds and loads, a 13-mode ESC test cycle has been carried out for EURO-IV and EURO-V emissions. Experimental results shows that it is possible to meet EURO-IV emissions with combined PCCI-DI combustion concept with economical aftertreatment solution.

Homogeneous Charge Compression Ignition (HCCI) combustion concept has potential of reducing NOx and PM emissions simultaneously and it is being considered as a future technology for diesel engines to meet tightened emission norms imposing by national governments. However, HCCI is limited to a narrow band of operating region due to difficulties in controlling combustion phasing close to Top Dead Center (TDC). From literature study, Exhaust Gas Recirculation (EGR), Intake Temperature, Boost Pressure, Equivalence Ratio and Compressions ratios are considered as most critical parameters for HCCI control. The chemical kinetics study was conducted to understand the HCC combustion using N-heptane mechanism with 162 species and 732 reactions. At lower equivalence ratio (lean burn combustion) higher CO and HC emissions were observed. The combustion efficiency was poor at lower temperatures, which resulted in high HC and CO emissions with less than 10ppm NOx.

This paper reviews the current research work on Homogeneous Charge Compression Ignition (HCCI) concept for diesel engines to meet future tightened emission norms. Heavy duty diesel engines are facing conflict between the goal of emission reduction and optimization of fuel consumption. In response to social demands and progressively strengthened emission regulations, diesel engines have been made cleaner through various means such as the combustion chamber, high pressure fuel injection, and turbocharger. In recent years, high pressure fuel injection has been considered as an effective method to reduce Particulate Matter (PM) by improving atomization and better air utilization, however, resulting in an increased Nitric Oxides (NOx) formation due to high temperature combustion. To fulfill future tightened emission norms, further developments on diesel engine technology and combustion improvements are required for simultaneous reduction of NOx and PM emissions as opposed to a trade-off.