Effects of Charge Preheating Methods on the Combustion Phasing Limitations of an HCCI Engine With Negative Valve Overlap

2012 ◽  
Vol 134 (11) ◽  
Author(s):  
Laura Manofsky Olesky ◽  
Jiri Vavra ◽  
Dennis Assanis ◽  
Aristotelis Babajimopoulos
Keyword(s):  
Combustion Stability ◽  
Residual Fraction ◽  
Nox Emissions ◽  
Indicated Mean Effective Pressure ◽  
Hcci Combustion ◽  
Final Study ◽  
Temperature Constant ◽  
Gas Dilution ◽  
Negative Valve Overlap ◽  
Valve Overlap

Homogeneous charge compression ignition (HCCI) has the potential to reduce both fuel consumption and NOx emissions 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 load of ∼3 bar gross indicated mean effective pressure (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 of these 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 versus residual gas 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 for higher intake temperatures, combustion is more susceptible to ringing at advanced timings and more resistant to instability/misfire at retarded timings.

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.

Study of diesel-fuelled homogeneous charge compression ignition combustion by in-cylinder early fuel injection and negative valve overlap

2005 ◽  
Vol 219 (10) ◽  
pp. 1193-1201 ◽  
Author(s):  
L Shi ◽  
K Deng ◽  
Y Cui
Keyword(s):  
Homogeneous Charge Compression Ignition ◽  
Ignition Time ◽  
Combustion Stability ◽  
Inlet Temperature ◽  
Compression Ignition ◽  
Engine Load ◽  
Hcci Combustion ◽  
Negative Valve Overlap ◽  
Valve Overlap ◽  
Homogeneous Charge

This paper presents a scheme to achieve diesel-fuelled homogeneous charge compression ignition (HCCI) combustion, which is to inject diesel fuel directly into the cylinder at near intake top dead centre and adjust the valve overlap to obtain a higher internal exhaust gas recirculation (EGR) in the cylinder. The effects of the engine load, speed, inlet temperature, external EGR, and internal EGR on HCCI combustion and emission were studied. The combustion stability of HCCI combustion was also studied by statistics analysis. The results show the following: when the engine load or inlet temperature increases, which results in a higher in-cylinder temperature, the start of combustion (SOC) is advanced; the ignition time of HCCI relative to the engine crank angle is retarded when the engine speed increases; inert gases contained in the EGR can slow the chemical reaction rate, which can delay the auto ignition time; for the diesel-fuelled HCCI, increasing the negative valve overlap (NVO) makes the SOC advanced and makes the combustion stability better at low loads and worse at high loads. The emission results show that the nitrogen oxides (NOx) and smoke emissions are very low, and a large NVO can decrease the smoke emission but not benefit the NOx emission at high loads for diesel-fuelled HCCI combustion.

scholarly journals Effects of spark assist on HCCI combustion

2015 ◽  
Vol 161 (2) ◽  
pp. 73-77
Author(s):  
Jacek HUNICZ ◽  
Michał GĘCA ◽  
Paweł KORDOS ◽  
Alejandro MEDINA
Keyword(s):  
Flame Propagation ◽  
Pressure Rise ◽  
Spark Discharge ◽  
Combustion Stability ◽  
Experimental Heat ◽  
Hcci Combustion ◽  
Auto Ignition ◽  
Negative Valve Overlap ◽  
Compression Ignition Combustion ◽  
Valve Overlap

HCCI (homogeneous charge compression ignition) combustion is initiated by compression temperature and is independent of spark discharge. However, spark discharge can be applied under certain conditions to achieve hybrid combustion, where combustion by flame propagation is followed by auto-ignition of the unburned mixture. Spark assist can be applied to improve combustion stability at low loads or to reduce pressure rise rates under high load regime. In the current study variable spark ignition timing was applied for stoichiometric HCCI combustion, achieved using negative valve overlap technique. Under investigated conditions increase of nitrogen oxides emissions, due to flame propagation, was not observed. To provide more insight into combustion evolution, double Wiebe function was fitted to experimental heat release rates. It was found that only less than 10% of mixture was burned by flame propagation, even for very advanced spark discharge.

The effect of advanced ignition system on gasoline low temperature combustion

2019 ◽  
pp. 146808741986754
Author(s):  
Hanho Yun ◽  
Cherian Idicheria ◽  
Paul Najt
Keyword(s):  
Low Temperature ◽  
Nox Emissions ◽  
Low Temperature Combustion ◽  
Efficiency Gain ◽  
Ignition System ◽  
Stable Combustion ◽  
Indicated Mean Effective Pressure ◽  
Spark Plug ◽  
Temperature Combustion ◽  
Valve Overlap

Engines operating in low temperature combustion during positive valve overlap operation offer significant benefits of high fuel economy over the low temperature combustion during negative valve overlap operation. Significant efficiency improvement was achieved by the increased gamma and lower pumping loss. However, NOx emissions were increased due to reliance on the flame-induced combustion. In this study, the corona ignition system was evaluated to reduce NOx emissions during positive valve overlap operation while maintaining the benefit of efficiency gain. The tests were performed in a 2.2-L multi-cylinder engine. The results show that the ignition delay is always shorter with the corona ignition system than with the spark plug. The corona ignition system is able to support stable combustion (coefficient of variation of indicated mean effective pressure <3%) in a lower load during positive valve overlap operation than the spark plug, which gives us additional efficiency benefit. Since the corona ignition system promotes simultaneous ignition of the mixture at multiple locations in the combustion chamber as opposed to ignition being limited to the spark gap channel, the dependence of the flame burn for stable combustion during positive valve overlap operation minimizes, which leads to lower NOx emissions over the spark plug.

Effect of Fuel Injection Timing During Negative Valve Overlap Period on a GDI-HCCI Engine

2018 ◽  
Author(s):  
Sok Ratnak ◽  
Jin Kusaka ◽  
Yasuhiro Daisho ◽  
Kei Yoshimura ◽  
Kenjiro Nakama
Keyword(s):  
Fuel Injection ◽  
Direct Injection ◽  
Single Pulse ◽  
Injection Timing ◽  
Pulse Injection ◽  
Hcci Combustion ◽  
Fuel Injection Timing ◽  
Intake Stroke ◽  
Negative Valve Overlap ◽  
Valve Overlap

Gasoline Direct Injection Homogeneous Charge Compression (GDI-HCCI) combustion is achieved by closing early the exhaust valves for trapping hot residual gases combined with direct fuel injection. The combustion is chemically controlled by multi-point auto-ignition which its main combustion phase can be controlled by direct injection timing of fuel. This work investigates the effect of single pulse injection timing on a supercharged GDI-HCCI combustion engine by using a four-stroke single cylinder engine with a side-mounted direct fuel injector. Injection of primary reference fuel PRF90 under the near-stoichiometric-boosted condition is studied. The fuel is injected during negative valve overlap (NVO) or recompression period for fuel reformation under low oxygen concentration and the injection is retarded to intake stroke for the homogeneous mixture. It is found that the early fuel injection in NVO period advances the combustion phasing compared with the retarded injection in the intake stroke. Noticeable slower combustion rate from intake stroke fuel injection is obtained compared with the NVO injection due to charge cooling effect. Zero-dimensional combustion simulations with multiple chemical reaction mechanisms are simulated to provide chemical understanding from the effect of fuel injection timing on intermediate species generations. The species such as C2H4, C3H6, CH4, and H2 are found to be formed during the NVO injection period from the calculations. The effects of single pulse injection timings on combustion characteristics such pressure rise rate, combustion stability, and emissions are also discussed in this study.

An integrated model for negative valve overlap early injection HCCI combustion

2014 ◽  
Vol 87 (4) ◽  
pp. 341-353 ◽  
Author(s):  
Yong Gui ◽  
Kangyao Deng ◽  
Min Xu ◽  
Lei Shi ◽  
Youcheng Sun
Keyword(s):  
Integrated Model ◽  
Hcci Combustion ◽  
Negative Valve Overlap ◽  
Valve Overlap ◽  
Early Injection

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.

A Cycle-to-Cycle Method to Predict HCCI Combustion Phasing

2013 ◽  
Author(s):  
Adam Vaughan ◽  
Stanislav V. Bohac
Keyword(s):  
Fuel Efficiency ◽  
Stability Limit ◽  
Low Temperature Combustion ◽  
Combustion Instabilities ◽  
Hcci Combustion ◽  
Crank Angle ◽  
Temperature Combustion ◽  
The Stability ◽  
Negative Valve Overlap ◽  
Valve Overlap

Homogeneous Charge Compression Ignition (HCCI) is a low temperature combustion strategy that simultaneously improves fuel efficiency and lowers engine-out NOx emissions. Unfortunately, broad usage of HCCI is hampered by combustion instabilities and a limited operation envelope. To help understand these limitations, this paper treats individual cylinders in a production four-cylinder engine as dynamical systems that iterate CA90 (the crank angle where 90% of net heat release is achieved) cycle-to-cycle as the engine operates in an unboosted, negative valve overlap HCCI combustion mode. This approach is shown to provide qualitative understanding of the stability limit bifurcation behavior, while also enabling quantitative cycle-to-cycle predictions of combustion phasing across a wide variety of transient and steady-state conditions, right up to complete misfire.

Sign in / Sign up

Export Citation Format

Share Document