HCCI is stands for Homogeneous Charge Compression Ignition engines. First research was started by Onishi et al. in 1979. This engine has been investigated worldwide as this technology has not matured sufficiently. It could be used in either SI or CI configurations with high compression ratio (CR. In principle, there is no spark plug or injector inside the combustion chamber like SI or CI engines to control the combustion: auto-ignition occurs in multiple spots once the mixture has reached its chemical activation energy

Hairuddin, A. Aziz

Wandel, Andrew P.

Yusaf, Talal F.

English

University of Southern Queensland ePrints

HCCI Engine: Numerical and Experimental Approach A. Aziz Hairuddin Talal F. Yusaf Andrew P. Wandel  UNIVERSITY OF SOUTHERN QUEENSLAND  Outline  Introduction  Numerical Approach  Model formulation  Results and analysis  Experimental Approach  Engine Diagram  Preliminary test  Conclusion Introduction  What is HCCI engine?  It stands for Homogeneous Charge Compression Ignition engines.   First research was started by Onishi et al. in 1979.   This engine has been investigated worldwide as this technology has not matured sufficiently.   It could be used in either SI or CI configurations with high compression ratio (CR)   In principle, there is no spark plug or injector inside the combustion chamber like SI or CI engines to control the combustion: auto-ignition occurs in multiple spots once the mixture has reached its chemical activation energy.  Introduction  What is the difference?  SI engines: Requires spark plug and low CR  CI engines: Requires fuel injector and high CR  HCCI engines: Without spark plugs or fuel injectors. Can be configured using CI or SI mode with high CR – leads to high engine efficiency with low emissions level.  Source: Lawrence Livermore National Laboratory, https://www-pls.llnl.gov/?url=science_and_technology-chemistry-combustion Introduction  Combustion behaviour:  SI engines: It has flame propagation with longer combustion period  CI engines: Auto-ignite when the fuel is injected into hot compressed air  HCCI engines: Auto-ignite in multiple spots instantaneously with fast combustion period  Source: Engine Research Centre, University of Wisconsin, http://www.erc.wisc.edu/combustion.php Introduction  Homogeneous charge engine types HCCI [69] Homogeneous-charge spark-ignition [69] Stratified-charge spark-ignition [69] Spark-induced compression-ignition [66] PCCI, SCCI [69] Flame propagation Auto-ignition Time Dual fuel [69] Introduction  HCCI engines can operate using any type of fuels as long as the fuel can be vaporized and mixed with air before the ignition.   Fuel auto-ignition point is important to look at in order to get smooth engine operation: Different fuels will have different auto-ignition points as shown in below figure.  Figure Intake temperatures required for fuels to operate under HCCI mode with various compression ratios (Aceves & Flowers 2004). Introduction  HCCI advantages:  High engine efficiency relative to SI engines by employing high CR and fast combustion [2,3].   Ability to operate using a wide range of fuels [4].   Can be implemented in any engine configuration: automobile engines, stationary engines, high load engines or small size engines [5,6]   HCCI disadvantages:  Difficulties in controlling the auto-ignition and heat release rate at high load operation and achieving cold start [7,8].   Knocking due to sudden onset of the combustion behaviour, which reduces engine reliability due to high vibration effects: produces pinging sound which can he heard outside. Introduction  HCCI challenge:   To control the auto-ignition timing of the mixture because there is no spark plug or fuel injector to control the start of the combustion.   To achieve cold start.   To meet emission standards.   To control knock.  Numerical Approach  Zero-Dimensional Model without Turbulence and Mixing Models Model Formulation  Conservation of mass: 𝑑𝑚𝑑𝑡=  𝑚 𝑗𝑗    Conservation of species:  An n-heptane reduced chemical reaction mechanism was used [13].  The properties are similar to conventional diesel (e.g. cetane number)  Consists of 160 species and 770 elementary reactions 𝑑𝑌𝑖𝑑𝑡=𝜔𝑖 𝑊𝑖𝜌, 𝑖 = 1, … , 𝑛   Gas exchange process:  A gas exchange process takes place when inlet or exhaust valve is open.   One-dimensional, steady state, isentropic flow is used to model the process [16].  Model Formulation  Conservation of energy:  The equation was derived from the first law of thermodynamics for an open system to get the change in temperature. 𝑑𝑇𝑑𝑡=1𝐶𝑝−𝑃𝑣𝑇−  𝐻𝑖 −𝑃𝑣  𝑅𝑢 𝑊 𝑖𝑅𝑢𝑊 𝑑𝑌𝑖𝑑𝑡−𝑚 𝑚ℎ𝑗 − 𝑃𝑣 +1𝑚 𝑚 𝑗ℎ𝑗 − 𝑃𝑑𝑉𝑑𝑡+𝑑𝑄𝑑𝑡  Where the pressure was calculated using the ideal gas law equation:  𝑃 = 𝜌𝑇𝑅𝑢𝑊    Heat transfer:  Heat is transferred to the wall through convection and radiation.  Radiation heat transfer on HCCI engines is neglected because the effect is very small, due to low soot and low temperature combustion [14,15]  The modified Woschni equation by Chang et al. [14] was used.  Results and Analysis  Validation  The model was validated against numerical and experimental data from Guo et al. [17]: the fuel was injected at inlet manifold.  To account for mixing effects: the effective intake temperature was set 20°C higher than the intake temperature [17].  Cylinder bore 82.55 mm Stroke 114.3 mm Connecting rod length 254 mm Compression ratio 10 Engine speed 900 rpm Inlet valve open (IVO) 10° CA ATDC Inlet valve closed (IVC) 36° CA ABDC Exhaust valve open (EVO) 40° CA BBDC Exhaust valve closed (EVC) 5° CA ATDC Table 1   Engine parameter used in the simulation [17] Results and Analysis  Validation  The comparison between experimental and numerical data from Guo et al. [17] with the zero-dimensional model. The combustion phasing is in good agreement with the experimental data.  320 340 360 380 400012345x 106Crank AngleIn-cylinder Pressure (MPa)  Zero-D ModelExperiment [17]Guo et al. Model [17]Figure 1 Comparison between single-zone zero-dimensional model with experiment and another single-zone model using modified Woschni heat transfer model [17]. CR=10.0, N=900 rpm, Tin=40°C, Pin=95 kPa, AFR=50. Results and Analysis: Effect of intake temperature  Auto-ignition can be advanced once the intake temperature is increased.   Results from the current simulation were compared with experimental results [17] in Fig. 2(a) to validate the model over different operating temperatures: The results agreed well as did in Fig. 1.   320 330 340 350 360 370 380 390 400012345x 106Crank AngleIn-cylinder Pressure (MPa)  Experimental 25C [17]Experimental 57C [17]Zero-D 25CZero-D 57C(a) Figure 2 Effect of intake temperature on the in-cylinder pressure: CR=10.0, N=900 rpm, Pin=95 kPa, AFR=50 (a) Validated varying intake temperature.  Results and Analysis: Effect of intake temperature 320 340 360 380 400012345x 106Crank AngleIn-cylinder Pressure (MPa)  20 C40 C60 C70 CFigure 2 Effect of intake temperature on the in-cylinder pressure: CR=10.0, N=900 rpm, Pin=95 kPa, AFR=50 (b) Predicted in-cylinder pressure trend.  (b)  The predicted in-cylinder peak pressure starts to decrease even though the auto-ignition is advanced (Fig 2b).  Results and Analysis: Effect of equivalence ratio  The equivalence ratio (Φ) is a measure of how much fuel and air is being consumed in the combustion chamber.   Figure 3(a) shows validated result of different equivalence ratios compared to the experiment, again showing good agreement. 320 330 340 350 360 370 380 390 400012345x 106Crank AngleIn-cylinder Pressure (MPa)  Experimental at  0.35 [17]Zero-D at  0.35Experimental at  0.3 [17]Zero-D at  0.3(a) Figure 3 Effect of equivalence ratio on the in-cylinder pressure: CR=10.0, N=900 rpm, Tin=40°C, Pin=95 kPa (a) Validated varying equivalence ratio. Results and Analysis: Effect of equivalence ratio 320 340 360 380 4000123456x 106Crank AngleIn-cylinder Pressure (MPa)  0.250.30.40.5Figure 3 Effect of equivalence ratio on the in-cylinder pressure: CR=10.0, N=900 rpm, Tin=40°C, Pin=95 kPa (b) Predicted in-cylinder pressure trend.  (b)  The in-cylinder peak pressure trend keeps increasing with increasing equivalence ratio: will create knocking.  (b) Results and Analysis: Effect of hydrogen addition  Effective way to reduce ignition delay and improves engine efficiency [19].  Too much hydrogen will create knocking: the energy ratio should be less than 15% [20].  The auto-ignition point is advanced significantly with 1% hydrogen and the in-cylinder peak pressure keeps increasing with increasing hydrogen content.  320 340 360 380 400012345x 106Crank AngleIn-cylinder Pressure (MPa)  n-heptane1% H25% H215% H2Figure 4 Predicted effect of hydrogen addition on the in-cylinder pressure for fixed n-heptane injection: CR=10.0, N=900 rpm, Tin=40°C, Pin=95 kPa Experimental Approach  Engine: Single cylinder SI engine to be converted to HCCI engine  External heater to be installed on the intake air manifold  Hydrogen will be added later on: if the time like us! Experimental Approach 1 Engine 2 Dynamometer 3 Data logger 4 Fuel tank 5 ECU  6 Hydrogen electrolyser 7 Fuel injector 8 Hydrogen injector 9 Air intake heater 10 Airflow meter   Engine diagram Experimental Approach  Preliminary test Experimental Approach  Preliminary test: Problem Experimental Approach  Next modification: Experimental Approach  Next modification:  Carburetor system replaced by injector system  New 2kW heater installed before the injector  Wideband lambda sensor will be used Conclusion  HCCI: high combustion efficiency, low emissions levels, can use any fuels  Numerical:  Once the intake temperature is increased above a certain threshold, the in-cylinder peak pressure will decrease with increasing intake temperature.  The in-cylinder peak pressure keeps increasing with increasing equivalence ratio: will create knocking.  Increasing the hydrogen content will also increase the in-cylinder peak pressure: should be no more than 20%  In summary, the combustion phasing is advanced by increasing all the parameters (intake temperature, equivalence ratio and energy ratio).  Experimental:  Engine setup has to be completed as soon as possible: workshop work for a new heater is pending. ETA in 2 - 4 weeks!  Future work: Investigation of all these factors on HCCI engines’ performance.  

HCCI engine: numerical and experimental approach

http://eprints.usq.edu.au/22118/1/Hairuddin_Yusaf_Wandel_USQ_Combustion_Meeting_AV.pdf

HCCI engine: numerical and experimental approach

Abstract

Similar works

Full text

Available Versions

University of Southern Queensland ePrints