The role of the in-cylinder gas temperature and oxygen concentration over low load reactivity controlled compression ignition combustion efficiency

Previous studies on reactivity controlled compression ignition combustion indicated that, reducing the hydrocarbon and carbon monoxide emissions at low load conditions still remains a challenge because of lower in-cylinder temperatures due to lower global reactivity gradient and reduced oxidation process. Research in this direction has not been reported so far and with this motivation, an attempt has been made to increase the global reactivity gradient and oxidation of fuel–air mixture by converting the low reactivity fuel methanol into medium reactivity fuel. This is achieved by mixing high octane oxygenated fuel, methanol (Octane Number: 110), with an oxygenated better cetane and volatility fuels like polyoxymethylene dimethyl ether (Cetane Number: 78) and isobutanol (Cetane Number: 15). The medium reactivity fuel with multiple direct injection of diesel fuel timed the combustion of dual fuel–air mixture to avoid too late or too advanced combustion which are the prime factors in controlling the unburnt emissions in a low temperature combustion process. Four medium reactivity fuel samples, M80IB20, M60IB40, M90P10, and M80P20, on percentage volume basis have been prepared and tested on the modified on-road three-cylinder turbocharged common rail direct injection diesel engine to demonstrate higher indicated thermal efficiency and potential reduction in unburnt and oxides of nitrogen/particulate matter emissions from reactivity controlled compression ignition combustion. Experimental results show that, use of medium reactivity fuel with optimized diesel injection strategy resulted in 66% decrease in hydrocarbon emission and 74% decrease in carbon monoxide emission by enhancing the oxidation of fuel–air mixture at lower temperatures which is evidently noticed in the combustion characteristics. Further reduction in hydrocarbon and carbon monoxide emission of about 90% has been achieved by integrating the diesel oxidation catalyst with the engine.

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Injection Strategy in Natural Gas–Diesel Dual-Fuel Premixed Charge Compression Ignition Combustion under Low Load Conditions

Engineering ◽

10.1016/j.eng.2019.03.005 ◽

2019 ◽

Vol 5 (3) ◽

pp. 548-557 ◽

Cited By ~ 4

Author(s):

Hyunwook Park ◽

Euijoon Shim ◽

Choongsik Bae

Keyword(s):

Natural Gas ◽

Dual Fuel ◽

Compression Ignition ◽

Injection Strategy ◽

Low Load ◽

Compression Ignition Combustion ◽

Load Conditions

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Use of Early Exhaust Valve Opening to Improve Combustion Efficiency and Catalyst Effectiveness in a Multi-Cylinder RCCI Engine System: A Simulation Study

Volume 1: Large Bore Engines; Fuels; Advanced Combustion; Emissions Control Systems ◽

10.1115/icef2014-5534 ◽

2014 ◽

Cited By ~ 5

Author(s):

Anand Nageswaran Bharath ◽

Nitya Kalva ◽

Rolf D. Reitz ◽

Christopher J. Rutland

Keyword(s):

System Simulation ◽

Combustion Efficiency ◽

Exhaust Valve ◽

Exhaust Gas ◽

Gas Temperature ◽

Flow Rates ◽

Low Load ◽

Valve Opening ◽

Engine System ◽

Exhaust Gas Temperature

Low Temperature Combustion (LTC) strategies such as Reactivity Controlled Compression Ignition (RCCI) can result in significant improvements of fuel economy and emissions reduction. However, they can produce significant carbon monoxide and unburnt hydrocarbon emissions at low load operating conditions due to poor combustion efficiencies at these operating points, which is a consequence of the low combustion temperatures that cause the oxidation rates of these species to slow down. The exhaust gas temperature is also not high enough at low loads for effective performance of turbocharger systems and diesel oxidation catalysts (DOC). The DOC is extremely sensitive to exhaust gas temperature changes and lights off only when a certain temperature is reached, depending on the catalyst specifications. Uncooled EGR can increase combustion temperatures, thereby improving combustion efficiency, but high EGR concentrations of 50% or more are required, thereby increasing pumping work and reducing volumetric efficiency. However, with early exhaust valve opening, the exhaust gas temperature can be much higher, allowing lower EGR flow rates, and enabling activation of the DOC for more effective oxidization of unburnt hydrocarbons and CO in the exhaust. In this paper, a multi-cylinder engine system simulation of RCCI at low load operation with early exhaust valve opening is presented, along with consideration of the exhaust aftertreatment system. The combustion process is modeled using the 3D CFD code, KIVA, and the heat release rates obtained from this combustion are used in a GT-Power model of a turbocharged, multi-cylinder light-duty RCCI engine for a full system simulation. The post-turbine exhaust gas is fed into GT-Power’s aftertreatment model of the engine’s DOC to determine the catalyst response. It is confirmed that opening the exhaust valve earlier increases the exhaust gas temperature, and hence lower EGR flow rates are needed to improve combustion efficiency. It was also found that exhaust temperatures of around 457 K are required to light off the catalyst and oxidize the unburnt hydrocarbons and CO effectively. Performance of the DOC was drastically improved and higher amounts of unburnt hydrocarbons were oxidized by increasing the exhaust gas temperature.

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