Reed Hanson

Fuel reactivity controlled compression ignition (RCCI): a pathway to controlled high-efficiency clean combustion

A fuel reactivity controlled compression ignition (RCCI) concept is demonstrated as a promising method to achieve high efficiency – clean combustion. Engine experiments were performed in a heavy-duty test engine over a range of loads. Additionally, RCCI engine experiments were compared to conventional diesel engine experiments. Detailed computational fluid dynamics modelling was then used to explain the experimentally observed trends. Specifically, it was found that RCCI combustion is capable of operating over a wide range of engine loads with near zero levels of NO x and soot, acceptable pressure rise rate and ringing intensity, and very high indicated efficiency. For example, a peak gross indicated efficiency of 56 per cent was observed at 9.3 bar indicated mean effective pressure and 1300 rev/min. The comparison between RCCI and conventional diesel showed a reduction in NO x by three orders of magnitude, a reduction in soot by a factor of six, and an increase in gross indicated efficiency of 16.4 per cent (i.e. 7.9 per cent more of the fuel energy was converted to useful work). The simulation results showed that the improvement in fuel conversion efficiency was due both to reductions in heat transfer losses and improved control over the start- and end-of-combustion.

Reactivity controlled compression ignition combustion on a multi-cylinder light-duty diesel engine

Reactivity controlled compression ignition is a low-temperature combustion technique that has been shown, both in computational fluid dynamics modeling and single-cylinder experiments, to obtain diesel-like efficiency or better with ultra-low nitrogen oxide and soot emissions, while operating primarily on gasoline-like fuels. This paper investigates reactivity controlled compression ignition operation on a four-cylinder light-duty diesel engine with production-viable hardware using conventional gasoline and diesel fuel. Experimental results are presented over a wide speed and load range using a systematic approach for achieving successful steady-state reactivity controlled compression ignition combustion. The results demonstrated diesel-like efficiency or better over the operating range explored with low engine-out nitrogen oxide and soot emissions. A peak brake thermal efficiency of 39.0% was demonstrated for 2600 r/min and 6.9 bar brake mean effective pressure with nitrogen oxide emissions reduced by an order of magnitude compared to conventional diesel combustion operation. Reactivity controlled compression ignition emissions and efficiency results are compared to conventional diesel combustion operation on the same engine.

Investigation of Combustion Phasing Control Strategy During Reactivity Controlled Compression Ignition (RCCI) Multicylinder Engine Load Transitions

The dual fuel reactivity controlled compression ignition (RCCI) concept has been successfully demonstrated to be a promising, more controllable, high efficiency and cleaner combustion mode. A multi-dimensional computational fluid dynamics (CFD) code coupled with detailed chemistry, KIVA-CHEMKIN, was applied to develop a strategy for phasing control during load transitions. Steady-state operating points at 1500 rev/min were calibrated from 0 to 5 bar brake mean effective pressure (BMEP). The load transitions considered in this study included a load-up and a load-down load change transient between 1 bar and 4 bar BMEP at 1500 rev/min. The experimental results showed that during the load transitions, the diesel injection timing responded in 2 cycles while around 5 cycles were needed for the diesel common-rail pressure to reach the target value. However, the intake manifold pressure lagged behind the pedal change for about 50 cycles due to the slower response of the turbocharger.The effect of these transients on RCCI engine combustion phasing was studied. The CFD model was first validated against steady-state experimental data at 1 bar and 4 bar BMEP. Then the model was used to develop strategies for phasing control by changing the direct port fuel injection (PFI) amount during load transitions. Specific engine operating cycles during the load transitions (6 cycles for the load-up transition and 7 cycles for the load-down transition) were selected based on the change of intake manifold pressure to represent the transition processes. Each cycle was studied separately to find the correct PFI to diesel fuel ratio for the desired CA50 (the crank angle at which 50 % of total heat release occurs). The simulation results showed that CA50 was delayed by 7 to 15 degrees for the load-up transition and advanced by around 5 degrees during the load-down transition if the pre-calibrated steady-state PFI table was used. By decreasing the PFI ratio by 10 % to 15 % during the load-up transition and increasing the PFI ratio by around 40 % during the load-down transition, the CA50 could be controlled at a reasonable value during transitions. The control strategy can be used for closed-loop control during engine transient operating conditions. Combustion and emission results during load transitions are also discussed.Copyright

Investigation of Combustion Phasing Control Strategy During Reactivity Controlled Compression Ignition (RCCI) Multi-Cylinder Engine Load Transitions

The dual fuel reactivity controlled compression ignition (RCCI) concept has been successfully demonstrated to be a promising, more controllable, high efficiency and cleaner combustion mode. A multi-dimensional computational fluid dynamics (CFD) code coupled with detailed chemistry, KIVA-CHEMKIN, was applied to develop a strategy for phasing control during load transitions. Steady-state operating points at 1500 rev/min were calibrated from 0 to 5 bar brake mean effective pressure (BMEP). The load transitions considered in this study included a load-up and a load-down load change transient between 1 bar and 4 bar BMEP at 1500 rev/min. The experimental results showed that during the load transitions, the diesel injection timing responded in 2 cycles while around 5 cycles were needed for the diesel common-rail pressure to reach the target value. However, the intake manifold pressure lagged behind the pedal change for about 50 cycles due to the slower response of the turbocharger.The effect of these transients on RCCI engine combustion phasing was studied. The CFD model was first validated against steady-state experimental data at 1 bar and 4 bar BMEP. Then the model was used to develop strategies for phasing control by changing the direct port fuel injection (PFI) amount during load transitions. Specific engine operating cycles during the load transitions (6 cycles for the load-up transition and 7 cycles for the load-down transition) were selected based on the change of intake manifold pressure to represent the transition processes. Each cycle was studied separately to find the correct PFI to diesel fuel ratio for the desired CA50 (the crank angle at which 50 % of total heat release occurs). The simulation results showed that CA50 was delayed by 7 to 15 degrees for the load-up transition and advanced by around 5 degrees during the load-down transition if the pre-calibrated steady-state PFI table was used. By decreasing the PFI ratio by 10 % to 15 % during the load-up transition and increasing the PFI ratio by around 40 % during the load-down transition, the CA50 could be controlled at a reasonable value during transitions. The control strategy can be used for closed-loop control during engine transient operating conditions. Combustion and emission results during load transitions are also discussed.Copyright

Investigation of Injection Strategies to Improve High Efficiency RCCI Combustion With Diesel and Gasoline Direct Injection

Experiments were performed to investigate injection strategies for improving engine-out emissions of RCCI combustion in a heavy-duty diesel engine. Previous studies of RCCI combustion using port-injected low-reactivity fuel (e.g., gasoline or iso-octane) and direct-injected high-reactivity fuel (e.g., diesel or n-heptane) have reported greater than 56% gross indicated thermal efficiency while meeting the EPA 2010 heavy-duty PM and NOx emissions regulations in-cylinder. However, CO and UHC emissions were higher than in diesel combustion. This increase is thought to be caused by crevice flows of trapped low-reactivity fuel and lower cylinder wall temperatures. In the present study, both the low- and high-reactivity fuels were direct-injected, enabling more precise targeting of the low-reactivity fuel as well as independent stratification of equivalence ratio and reactivity. Experiments with direct-injection of both gasoline and diesel were conducted at 9 bar IMEP and compared to results from experiments with port-injected gasoline and direct-injected diesel at matched conditions. The results indicate that reductions in UHC, CO, and PM are possible with direct-injected gasoline, while maintaining similar gross indicated efficiency as well as NOx emissions well below the EPA 2010 heavy-duty limit. Additionally, experimental results were simulated using multi-dimensional modeling in the KIVA-3V code coupled to a Discrete Multi-Component fuel vaporization model. The simulations suggest that further UHC reductions can be made by using wider injector angles which direct the gasoline spray away from the crevices.Copyright

Evolution and current understanding of physicochemical characterization of particulate matter from reactivity controlled compression ignition combustion on a multicylinder light-duty engine

Low-temperature compression ignition combustion can result in nearly smokeless combustion, as indicated by a smoke meter or other forms of soot measurement that rely on absorbance due to elemental carbon content. Highly premixed low-temperature combustion modes do not form particulate matter in the traditional pathways seen with conventional diesel combustion. Previous research into reactivity controlled compression ignition particulate matter has shown, despite a near zero smoke number, significant mass can be collected on filter media used for particulate matter certification measurement. In addition, particulate matter size distributions reveal that a fraction of the particles survive heated double-dilution conditions. This study summarizes research completed at Oak Ridge National Laboratory to date on characterizing the nature, chemistry and aftertreatment considerations of reactivity controlled compression ignition particulate matter and presents new research highlighting the importance of injection strategy and fuel composition on reactivity controlled compression ignition particulate matter formation. Particle size measurements and the transmission electron microscopy results do show the presence of soot particles; however, the elemental carbon fraction was, in many cases, within the uncertainty of the thermal–optical measurement. Particulate matter emitted during reactivity controlled compression ignition operation was also collected with a novel sampling technique and analyzed by thermal desorption or pyrolysis gas chromatography mass spectroscopy. Particulate matter speciation results indicated that the high boiling range of diesel hydrocarbons was likely responsible for the particulate matter mass captured on the filter media. To investigate potential fuel chemistry effects, either ethanol or biodiesel were incorporated to assess whether oxygenated fuels may enhance particle emission reduction.

Investigation of Cold Starting and Combustion Mode Switching as Methods to Improve Low Load RCCI Operation

Reactivity controlled compression ignition (RCCI) is an engine combustion strategy that utilizes in-cylinder fuel blending to produce low NOx and particulate matter (PM) emissions while maintaining high thermal efficiency. The current study investigates RCCI and conventional diesel combustion (CDC) operation in a light-duty multicylinder engine (MCE) using a transient capable engine test cell. The main focus of the work uses engine experiments to investigate methods which can improve low load RCCI operation. The first set of experiments investigated RCCI operation during cold start conditions. The next set of tests investigated combustion mode switching between RCCI and CDC. During the cold start tests, RCCI performance and emissions were measured over a range of engine coolant temperatures (ECTs) from 48 °C to 85 °C. A combination of open- and closed-loop controls enabled RCCI to operate at a 1500 rpm, 1 bar BMEP operating point over this range of coolant temperatures. At a similar operating condition, i.e., 1500 rpm, 2 bar BMEP, the engine was instantaneously switched between CDC and RCCI combustion using the same open- and closed-loop controls as the cold start testing. During the mode switch tests, emissions and performance were measured with high-speed sampling equipment. The tests revealed that it was possible to operate RCCI down to 48 °C with simple open- and closed-loop controls with emissions and efficiency similar to the warm steady-state values. Next, the mode switching tests were successful in switching combustion modes with minimal deviations in emissions and performance in either mode at steady state.

Effects of biofuel blends on transient reactivity-controlled compression ignition engine combustion

Reactivity-controlled compression ignition is a low-temperature engine combustion strategy that utilizes in-cylinder blending of fuels with different autoignition characteristics to produce low NOx (oxides of nitrogen) and particulate matter emissions while maintaining high thermal efficiency. This study investigates reactivity-controlled compression ignition combustion in a light-duty, multi-cylinder, compression ignition engine over steady-state and transient operating conditions with both petroleum and bio-derived fuels. The engine experiments consisted of in-cylinder fuel blending with port fuel injection of gasoline or E20 and early-cycle, direct injection of ultra-low sulfur diesel or B20. Performance and emissions results were compared at steady-state and over an up-load change between 1 and 4 bar brake mean effective pressure at 1500 r/min. The results under steady-state operation showed that E20 offered reduced hydrocarbon emissions from the lower port fuel injection mass fraction. Port fuel injection mass fraction is defined as the mass fraction of the port fuel injection injected fuel compared to the total fuel injected, as calculated by P F I f r a c t i o n = ( M . P F I ) / ( M . P F I + M . D I ) . E20 also was shown to offer higher peak load capability and thermal efficiency than gasoline. Conversely, B20 was found to require a higher port fuel injection mass fraction with resulting higher hydrocarbon emissions. Peak load and efficiency were not affected by the use of B20. Steady-state NO and particulate matter emissions were unaffected by either of the biofuels. During the transient tests, E20 reduced hydrocarbon emissions while B20 increased hydrocarbon emissions. Both biofuels offered faster transient response to recover the CA50 to the steady-state CA50 value than gasoline or ultra-low sulfur diesel.

Fuel economy and emissions testing of an RCCI series hybrid vehicle

In the current work, a series hybrid vehicle has been constructed that utilises a dual-fuel, reactivity controlled compression ignition (RCCI) engine. Full vehicle testing was conducted on chassis dynamometers over the US Environmental Protection Agency Federal Test Procedure, Highway Fuel Economy Test and US06 using RCCI combustion with commercially available gasoline and ultra-low sulphur diesel. Fuel economy and emissions data were recorded over the specified test cycles. Testing revealed that engine-out emissions were similar to steady-state dynamometer engine testing. However, tailpipe-out emissions saw a reduction of HC and CO during the HWFET of 98.5%. Fuel economy was lower than expected due to the higher drivetrain losses of the series hybrid drivetrain. Finally, simulated changes to the drivetrain showed that it may be possible to increase fuel economy significantly, while meeting EPA emissions standards.