Variable valve actuation–based combustion control strategies for efficiency improvement and emissions control in a heavy-duty diesel engine

Abstract

High nitrogen oxide levels of the conventional diesel engine combustion often requires the introduction of exhaust gas recirculation at high engine loads. This can adversely affect the smoke emissions and fuel conversion efficiency associated with a reduction of the in-cylinder air-fuel ratio (lambda). In addition, low exhaust gas temperatures at low engine loads reduce the effectiveness of aftertreatment systems necessary to meet stringent emissions regulations. These are some of the main issues encountered by current heady-duty diesel engines. In this work, variable valve actuation–based advanced combustion control strategies have been researched as means of improving upon the engine exhaust temperature, emissions, and efficiency. Experimental analysis was carried out on a single-cylinder heady-duty diesel engine equipped with a high-pressure common-rail fuel injection system, a high-pressure loop cooled exhaust gas recirculation, and a variable valve actuation system. The variable valve actuation system enables a late intake valve closing and a second intake valve opening during the exhaust stroke. The results showed that Miller cycle was an effective technology for exhaust temperature management of low engine load operations, increasing the exhaust gas temperature by 40 °C and 75 °C when running engine at 2.2 and 6 bar net indicated mean effective pressure, respectively. However, Miller cycle adversely effected carbon monoxide and unburned hydrocarbon emissions at a light load of 2.2 bar indicated mean effective pressure. This could be overcome when combining Miller cycle with a second intake valve opening strategy due to the formation of a relatively hotter in-cylinder charge induced by the presence of internal exhaust gas recirculation. This strategy also led to a significant reduction in soot emissions by 82% when compared with the baseline engine operation. Alternatively, the use of external exhaust gas recirculation and post injection on a Miller cycle operation decreased high nitrogen oxide emissions by 67% at a part load of 6 bar indicated mean effective pressure. This contributed to a reduction of 2.2% in the total fluid consumption, which takes into account the urea consumption in aftertreatment system. At a high engine load of 17 bar indicated mean effective pressure, a highly boosted Miller cycle strategy with exhaust gas recirculation increased the fuel conversion efficiency by 1.5% while reducing the total fluid consumption by 5.4%. The overall results demonstrated that advanced variable valve actuation–based combustion control strategies can control the exhaust gas temperature and engine-out emissions at low engine loads as well as improve upon the fuel conversion efficiency and total fluid consumption at high engine loads, potentially reducing the engine operational costs.

Development of a Variable Valve Actuation Control to Improve Diesel Oxidation Catalyst Efficiency and Emissions in a Light Duty Diesel Engine

“…This characteristic also prevents an increase in soot emissions. The combination of EGR and LIVC helped to improve the NO x -soot trade-off relation [13,14]. Similarly, Zhou et al [17] achieved a reduction in particle matter emissions by 32.9%, with a small increase in NO x by applying LIVC strategy and an optimal control of the VGT (Variable Geometry Turbine) and EGR during realistic transient conditions.…”

“…Consequently, some of the air flows back into the intake manifold, leading to a reduction in the effective compression ratio and a lambda reduction (lower combustion chamber charge). These two consequences lead to a higher exhaust gas temperatures and a NO x engine-out emission reduction [12][13][14]. However, Maniatis et al [15] experiments did not find any advantage in exhaust gas enthalpy or a reduction of HC and CO emissions.…”

Diesel engine optimization and exhaust thermal management by means of variable valve train strategies

“…These two consequences lead to a higher exhaust gas temperatures and a NO x engine-out emission reduction. 9–11 However, Maniatis et al 12 experiments found neither any benefit in exhaust gas enthalpy nor a reduction of HC and CO emissions. Kim and Choongsik 13 found that the amount of EGR could be reduced to maintain a similar level of NO x emissions when the IVC timing is retarded.…”

“…The combination of EGR and LIVC helped to improve the NO x -soot trade-off relation. 10,11 Similarly, Zhou et al 14 achieved a reduction in particle matter emissions by 32.9% with a small increase in NO x by applying LIVC strategy and an optimal control of the variable geometry turbine (VGT) and EGR during realistic transient conditions.…”

Utilizing Exhaust Valve Opening Modulation for Fast Warm-up of Exhaust After-treatment Systems on Highway Diesel Vehicles

“…Modulating intake valve closure (IVC) is one way to rise exhaust temperatures [17,18]. Retarding or advancing nominal IVC timing decreases air intake and increases engineout temperatures.…”