Low Load Limit Extension for Gasoline Compression Ignition Using Negative Valve Overlap Strategy

2018 ◽  
Author(s):  
R. Vallinayagam ◽  
Abdullah S. AlRamadan ◽  
S Vedharaj ◽  
Yanzhao An ◽  
Jaeheon Sim ◽  
...  
Keyword(s):  
Compression Ignition ◽  
Load Limit ◽  
Low Load ◽  
Negative Valve Overlap ◽  
Valve Overlap

The Low Load Limit of Gasoline Partially Premixed Combustion Using Negative Valve Overlap

2012 ◽  
Author(s):  
Patrick Borgqvist ◽  
Öivind Andersson ◽  
Per Tunestål ◽  
Bengt Johansson
Keyword(s):  
Engine Speed ◽  
Premixed Combustion ◽  
Partially Premixed Combustion ◽  
Operating Region ◽  
Load Limit ◽  
Low Load ◽  
Negative Valve Overlap ◽  
Valve Overlap ◽  
Injection Strategies ◽  
High Octane

Partially premixed combustion has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in PPC mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions, even at higher loads. The problem is the ignitability at low load and idle operating conditions. The objective is to investigate different multiple-injection strategies in order to further expand the low load limit and reduce the dependency on negative valve overlap in order to increase efficiency. The question is, what is the minimum attainable load for a given setting of negative valve overlap and fuel injection strategy. The experimental engine is a light duty diesel engine equipped with a fully flexible valve train system. The engine is run without boost at engine speed 800 rpm. The fuel is 87 RON gasoline. A turbocharger is typically used to increase the boost pressure, but at low engine speed and load the available boost is expected to be limited. The in-cylinder pressure and temperature around top-dead-center will then be too low to ignite high octane number fuels. A negative valve overlap can be used to extend the low engine speed and load operating region. But one of the problems with negative valve overlap is the decrease in gas-exchange efficiency due to heat-losses from recompression of the residual gases. Also, the potential temperature increase from the trapped hot residual gases is limited at low load due to the low exhaust gas temperature. In order to expand the low load operating region further, more advanced injection strategies are investigated.

The Low Load Limit of Gasoline Partially Premixed Combustion Using Negative Valve Overlap

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Patrick Borgqvist ◽  
Öivind Andersson ◽  
Per Tunestål ◽  
Bengt Johansson
Keyword(s):  
Engine Speed ◽  
Premixed Combustion ◽  
Partially Premixed Combustion ◽  
Operating Region ◽  
Load Limit ◽  
Low Load ◽  
Partially Premixed ◽  
Negative Valve Overlap ◽  
Valve Overlap ◽  
Injection Strategies

Partially premixed combustion has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in partially premixed combustion mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions, even at higher loads. The problem is the ignitability at low load and idle operating conditions. The objective is to investigate different multiple-injection strategies in order to further expand the low load limit and reduce the dependency on negative valve overlap in order to increase efficiency. The question is, what is the minimum attainable load for a given setting of negative valve overlap and fuel injection strategy. The experimental engine is a light duty diesel engine equipped with a fully flexible valve train system. The engine is run without boost at engine speed 800 rpm. The fuel is 87 RON gasoline. A turbocharger is typically used to increase the boost pressure, but at low engine speed and load the available boost is expected to be limited. The in-cylinder pressure and temperature around top-dead-center will then be too low to ignite high octane number fuels. A negative valve overlap can be used to extend the low engine speed and load operating region. But one of the problems with negative valve overlap is the decrease in gas-exchange efficiency due to heat-losses from recompression of the residual gases. Also, the potential temperature increase from the trapped hot residual gases is limited at low load due to the low exhaust gas temperature. In order to expand the low load operating region further, more advanced injection strategies are investigated.

Numerical study on combustion characteristics of six-stroke-cycle gasoline compression ignition engine with continuously variable valve duration valve technology

2019 ◽  
Vol 22 (1) ◽  
pp. 165-183 ◽  
Author(s):  
Oudumbar Rajput ◽  
Youngchul Ra ◽  
Kyoung-Pyo Ha ◽  
You-Sang Son
Keyword(s):  
Numerical Study ◽  
Power Stroke ◽  
Compression Ignition ◽  
Ignition Timing ◽  
Compression Ignition Engine ◽  
Engine Operation ◽  
Wide Range ◽  
Negative Valve Overlap ◽  
Variable Valve ◽  
Valve Overlap

Engine performance and emissions of a six-stroke gasoline compression ignition engine with a wide range of continuously variable valve duration control were numerically investigated at low engine load conditions. For the simulations, an in-house three-dimensional computational fluid dynamics code with high-fidelity physical sub-models was used, and the combustion and emission kinetics were computed using a reduced kinetics mechanism for a 14-component gasoline surrogate fuel. Variation of valve timing and duration was considered under both positive valve overlap and negative valve overlap including the rebreathing of intake valves via continuously variable valve duration control. Close attention was paid to understand the effects of two additional strokes of the engine cycle on the thermal and chemical conditions of charge mixtures that alter ignition, combustion and energy recovery processes. Double injections were found to be necessary to effectively utilize the additional two strokes for the combustion of overly mixed lean charge mixtures during the second power stroke. It was found that combustion phasing in both power strokes is effectively controlled by the intake valve closure timing. Engine operation under negative valve overlap condition tends to advance the ignition timing of the first power stroke but has minimal effect on the ignition timing of second power stroke. Re-breathing was found to be an effective way to control the ignition timing in second power stroke at a slight expense of the combustion efficiency. The operation of a six-stroke gasoline compression ignition engine could be successfully simulated. In addition, the operability range of the six-stroke gasoline compression ignition engine could be substantially extended by employing the continuously variable valve duration technique.

Controlling combustion with negative valve overlap in a gasoline–diesel dual-fuel compression ignition engine

2015 ◽  
Vol 17 (3) ◽  
pp. 354-365 ◽  
Author(s):  
Kohei Kuzuoka ◽  
Takashi Kondo ◽  
Hirotsugu Kudo ◽  
Hiroyoshi Taniguchi ◽  
Hiroshi Chishima ◽  
...  
Keyword(s):  
Dual Fuel ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Negative Valve Overlap ◽  
Valve Overlap

Internal Residual vs. Elevated Intake Temperature: How the Method of Charge Preheating Affects the Phasing Limitations of HCCI Combustion

2012 ◽  
Author(s):  
Laura Manofsky Olesky ◽  
Jiri Vavra ◽  
Dennis Assanis ◽  
Aristotelis Babajimopoulos
Keyword(s):  
Constant Load ◽  
Combustion Stability ◽  
Residual Fraction ◽  
Compression Ignition ◽  
Hcci Combustion ◽  
Final Study ◽  
Temperature Constant ◽  
Negative Valve Overlap ◽  
Burn Rate ◽  
Valve Overlap

Homogeneous charge compression ignition (HCCI) has the potential to reduce both fuel consumption and NOx emissons compared to normal spark-ignited (SI) combustion. For a relatively low compression ratio engine, high unburned temperatures are needed to initiate HCCI combustion, which is achieved with large amounts of internal residual or by heating the intake charge. The amount of residual in the combustion chamber is controlled by a recompression valve strategy, which relies on negative valve overlap (NVO) to trap residual gases in the cylinder. A single-cylinder research engine with fully-flexible valve actuation is used to explore the limits of HCCI combustion phasing at a constant load of ∼3 bar IMEPg. This is done by performing two individual sweeps of a) internal residual fraction (via NVO) and b) intake air temperature to control combustion phasing. It is found that increasing both variables advances the phasing of HCCI combustion, which leads to increased NOx emissions and a higher ringing intensity. On the other hand, a reduction in these variables leads to greater emissions of CO and HC, as well as a decrease in combustion stability. A direct comparison of the two sweeps suggests that the points with elevated intake temperatures are more prone to ringing as combustion is advanced and less prone to instability and misfire as combustion is retarded. This behavior can be explained by compositional differences (air vs. EGR dilution) which lead to variations in burn rate and peak temperature. As a final study, two additional NVO sweeps are performed while holding intake temperature constant at 30°C and 90°C. Again, it is seen that at higher intake temperatures, combustion is more susceptible to ringing at advanced timings and more resistant to instability/misfire at retarded timings.

Effects of a Low Octane Gasoline Blended Fuel on Negative Valve Overlap Enabled HCCI Load Limit, Combustion Phasing and Burn Duration

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Luke M. Hagen ◽  
Laura Manofsky Olesky ◽  
Stanislav V. Bohac ◽  
George Lavoie ◽  
Dennis Assanis
Keyword(s):  
Maximum Load ◽  
Heating Value ◽  
Hcci Combustion ◽  
Fuel Flow ◽  
Load Limit ◽  
Lower Heating Value ◽  
O2 Concentration ◽  
Negative Valve Overlap ◽  
Valve Overlap ◽  
Lower Heating

Homogeneous charge compression iginition (HCCI) combustion allows for the use of fuels with octane requirements below that of spark-ignited engines. A reference gasoline was compared with iso-octane and a low octane blend of gasoline and 40% n-heptane, NH40. Experiments were conducted on a single cylinder engine operating with negative valve overlap (NVO). The fuel flow rate per cycle was compensated based on the lower heating value to maintain a constant energy addition across fuels. Iso-octane and gasoline demonstrated similar maximum load, achieving a gross IMEPg of ~430 kPa, whereas the NH40 demonstrated an increased IMEPg of ~460 kPa. The NH40 could be operated at a later phasing compared with the higher octane fuels, and exhibited a shorter burn duration at a given fueling rate and phasing. These results could be due to compositional differences, as NH40 required less NVO compared to iso-octane and gasoline, leading to less thermal and compositional stratification, as well as a higher O2 concentration and less residual gas. Additionally, the NH40 fuel demonstrated a higher intermediate temperature heat release than the higher octane fuels, potentially contributing to the shorter burn duration. Overall, these results demonstrate clear benefits to NVO enabled HCCI combustion with low octane fuels.

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