Performance HCCI Ethanol Fuelled Engine

1,223 views

Published on

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,223
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
45
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Performance HCCI Ethanol Fuelled Engine

  1. 1. This article was downloaded by: [Universiti Teknologi Malaysia]On: 11 January 2013, At: 20:55Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK Combustion Science and Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gcst20 Predicting Fuel Performance for Future HCCI Engines a b a a Vi H. Rapp , William J. Cannella , J.-Y. Chen & Robert W. Dibble a Department of Mechanical Engineering, University of California–Berkeley, Berkeley, California, USA b Chevron Energy Technology Company, Richmond, California, USA Accepted author version posted online: 04 Dec 2012.To cite this article: Vi H. Rapp , William J. Cannella , J.-Y. Chen & Robert W. Dibble (2012): Predicting Fuel Performance forFuture HCCI Engines, Combustion Science and Technology, DOI:10.1080/00102202.2012.750309To link to this article: http://dx.doi.org/10.1080/00102202.2012.750309Disclaimer: This is a version of an unedited manuscript that has been accepted for publication. As a serviceto authors and researchers we are providing this version of the accepted manuscript (AM). Copyediting,typesetting, and review of the resulting proof will be undertaken on this manuscript before final publication ofthe Version of Record (VoR). During production and pre-press, errors may be discovered which could affect thecontent, and all legal disclaimers that apply to the journal relate to this version also.PLEASE SCROLL DOWN FOR ARTICLEFull terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditionsThis article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form toanyone is expressly forbidden.The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.
  2. 2. ACCEPTED MANUSCRIPT Predicting Fuel Performance for Future HCCI Engines Vi H. Rapp1,*, William J. Cannella2, J.-Y. Chen1, Robert W. Dibble1 1 Department of Mechanical Engineering, University of California–Berkeley, Berkeley, California, USA, 2Chevron Energy Technology Company, Richmond, California, USA *Corresponding author: E-mail: vhrapp@berkeley.eduDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 Abstract The purpose of this research is to investigate the impact of fuel composition on auto- ignition in HCCI engines in order to develop a future metric for predicting fuel performance in future HCCI engine technology. A single-cylinder, variable compression ratio engine operating as an HCCI engine was used to test reference fuels and gasoline blends with Octane numbers (ON) ranging from 60-88. Correlations between fuel composition, ON, and two existing methods for predicting fuel auto-ignition in HCCI engines (Kalghatgi’s Octane Index and Shibata and Urushihara’s HCCI Index) are investigated. Results show that Octane Index and HCCI Index poorly predict the impact of fuel composition on auto-ignition for fuels with the same ON. The effect of ethanol in delaying auto-ignition depends on the composition of the original gasoline blend; the same is true for the addition of naphthenes. Low temperature heat release (LTHR) correlates well with auto-ignition for gasoline fuels exhibiting LTHR. KEYWORDS: Auto-ignition, Homogenous charge compression-ignition (HCCI), Fuel composition INTRODUCTION ACCEPTED MANUSCRIPT 1
  3. 3. ACCEPTED MANUSCRIPT Increasing concern with climate change has encouraged the development of alternative fuels and advanced engine technologies that improve efficiency and reduce CO2 emissions. Homogeneous charge compression ignition (HCCI) engines offer the potential for Diesel-like efficiencies and low nitrogen oxide emissions compared with conventional gasoline and Diesel engines. HCCI engines also offer fuel flexibility as they can operate using a wide variety of fuels such as Diesel, gasoline, and alternative fuels (Thring, 1989; Fuhs, 2008). In the early twentieth century, Weiss and Mietz developed the first HCCI-Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 like combustion engine, called the hot-bulb engine (Erlandsson, 2002). The hot-bulb engine offered a simple and durable design that had brake thermal efficiencies comparable to contemporary Diesel engines. Later, in 1979, Onishi et al. (1979) published the first research on a gasoline-fueled HCCI engine. The two-stroke gasoline engine, using a process dubbed Active Thermo-Atmosphere Combustion (ATAC) by the authors, increased fuel economy and decreased exhaust emissions at part-throttle operation. In 1983, Najt and Foster (1983) achieved compression ignition homogenous charge (CIHC) combustion in a four-stroke gasoline engine. Using the same engine as Najt and Foster, Thring (1989) studied the effects of exhaust gas recirculation, intake temperature, and compression ratio; he was also the first to use the acronym HCCI. Seven years after Thring, the first research burning Diesel fuel in an HCCI engine appeared (Gray and Ryan, 1997) and led to research testing other fuels, such as alcohols (Oakley et al., 2001), hydrogen (Shudo and Ono, 2002), natural gas (Christensen, Johansson and Einewall, 1997; Hiltner et al., 2000; Olsson et al., 2002; Stanglmaier, Ryan and Souder, 2001), ACCEPTED MANUSCRIPT 2
  4. 4. ACCEPTED MANUSCRIPT propane(Au et al., 2001; Flowers et al., 2001), and many fuel blends with additives (Eng, Leppard and Sloane, 2003; Yao, Zheng and Liu, 2009) Although HCCI engines offer fuel flexibility and a solution for meeting new, strict pollution requirements, HCCI engines have a limited load range and cannot support high load demands required by automobiles. Hybrid HCCI engines, such as SI-HCCI (Zhang, Xie and Zhao, 2009; Koopmans et al., 2003), HCCI-DI (Canova et al., 2007; HelmantelDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 and Denbratt, 2004), or HCCI-electric(Wu and Zhang, 2012), offer a solution for reducing emissions and increasing the load operating range. As HCCI engine technology becomes more widely used in automotive technology, developing fuels to support hybrid HCCI engines will become increasingly important. Conventional methods for quantifying fuel auto-ignition, such as Research Octane Number (RON), Motor Octane Number (MON), Octane Number (ON = ½RON + ½MON) and Cetane Number, poorly predict auto-ignition in HCCI engines (Kalghatgi, 2005; Shibata and Urushihara, 2007). Kalghatgi (2005) developed an Octane Index (OI) for measuring the auto-ignition or anti-knock quality of a practical fuel at different operating conditions. The OI, not to be confused with ON, is defined as, OI = (1 K)RON + (K)MON, (1) where K is a parameter specified by engine operating conditions. Although the OI may be applicable for HCCI operation (Kalghatgi, 2005), the OI does not fully describe the impact of fuel composition on auto-ignition in HCCI engines. ACCEPTED MANUSCRIPT 3
  5. 5. ACCEPTED MANUSCRIPT Shibata and Urushihara (2007) investigated the impact of fuel composition on auto- ignition in HCCI engines and introduced three HCCI Indices. While all three HCCI Indices predict auto-ignition similarly, the relative HCCI Index (HIrel) predicts auto- ignition of fuels using the fuel composition and MON (Shibata and Urushihara, 2007). The HIrel is defined as, HI rel = MON + α(nP) +β(iP) (2) (O) δ(A) + (OX),Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 where nP is the percent n-paraffins by volume, iP is the percentiso-paraffins by volume, O is the percent olefins and cycloalkanes by volume, A is the percent aromatics by volume, OX is the percent oxygenates by volume, and α, β, γ, δ, and ε are temperature dependent parameters. In this paper, the capability of two existing methods (the OI and the HIrel) for predicting the impact of fuel composition on auto-ignition in HCCI engines is investigated and correlations between fuel composition and auto-ignition of fuels in a HCCI engine are explored. Fuels tested consist of following five different blends: 1. Primary reference fuels (PRF):blends of isooctane and n-heptane 2. Toluene reference fuels (TRF): PRF fuels blended with toluene 3. Ethanol reference fuels(E-PRF): PRF fuels blended with Ethanol 4. Gasoline blendstocks 5. Gasoline blendstocks with different pure compounds added (“additives”) ACCEPTED MANUSCRIPT 4
  6. 6. ACCEPTED MANUSCRIPT Following this Introduction, the instrumentation and experimental design are described. Next, results and discussions are presented. Last, future work is suggested and conclusions are drawn. MATERIALS AND METHODS Engine and Fuel Specifications Similar to previous metrics for predicting fuel auto-ignition, such as RON and MONDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 (ASTM RON Standard, 2011; ASTM MON Standard, 2011), experiments were conducted using a variable compression ratio, single cylinder cooperative fuel research (CFR) engine operating in HCCI mode. Engine specifications and operating conditions are listed in Table 1. The engine was preheated by operating in spark-ignition mode under stoichiometric conditions. Once the coolant temperature reached 80°C, the equivalence ratio was decreased to =0.33 ( =3.0). Next, the compression ratio (CR) was slowly increased until stable auto-ignition (no misfiring) occurred. The lowest CR limit was determined by decreasing the CR until HCCI operation became unstable. The highest CR limit for each fuel was determined by increasing the CR until the in-cylinder pressure exceeded 50 bar (a limit to safe guard the mechanical integrity of CFR engine) or the ringing intensity became too great (Eng, 2002). For each experiment, equivalence ratio was held constant at φ=0.33 (λ=3.0). Data were taken at various compression ratios between the lowest and the highest limits. For a fixed CR, 300 thermodynamic cycles (each cycle with 720 CAD) of in-cylinder pressure data were collected along with exhaust emissions before the catalytic converter. ACCEPTED MANUSCRIPT 5
  7. 7. ACCEPTED MANUSCRIPT The effects of fuel composition on auto-ignition timing n HCCI engines, measured by CA50 (the crank angle degree at which 50% of the cumulative heat has been released),was explored by testing twenty different fuel blends at an engine intake temperature of 150°C and one fuel, PRF70, at intake temperatures of 70°C, 115°C, and 150°C. Of the twenty fuels, eight fuels were reference fuel blends. The reference fuel blends consisted of PRF60, PRF70, PRF75, PRF85, PRF88, TRF70, S70, and E-PRF70. For primary reference fuels (PRF), the number following "PRF" is the RON, MON, andDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 percent isooctane by volume. TRF70 (46% n-heptane and 54% toluene, by volume) has a calculated RON of 70.5and MON of 63.5, which were calculated using a linear-by- volume blending equation created by Morgan et al.(2010). For S70 (64% isooctane, 31% n-heptane, and 5% toluene by volume) the RON and MON were measured, by Chevron, as 70.5and 69.6, respectively. A RON of 69.5 and MON of 68.6 were calculated for E- PRF70 (64% isooctane, 31% n-heptane, and 5% ethanol by volume) using the blending RON and blending MON values from Anderson et al.(2010). A summary of the reference fuel blend compositions, RON, and MON are given in Table 2. Two different base gasolines, typically used in U.S. gasoline blends, were provided by Chevron, labeled G1 and G2. Hydrocarbon class information and the RON and MON of the base gasolines are provided in Table 3. The base gasoline fuels were blended with different “additives”: n-heptane, ethanol, cycloparaffins, and aromatics. RON and MON for the gasoline fuel blends are listed in Table 4along with the type of additive. Fuels with a calculated RON and MON were determined using the blending RON and blending MON of the additive. ACCEPTED MANUSCRIPT 6
  8. 8. ACCEPTED MANUSCRIPT Determining Octane Index, Relative HCCI Index, And Heat Release The K factor for the OI, shown in Eq. (1), is a function of the in-cylinder temperature when the in-cylinder pressure, during the compression stroke, reaches 15 bar (Tcomp,15bar) (Kalghatgi, 2005). The K factor is computed using the following equations: K = 0.0426 (Tcomp,15bar ) 35.2 if Tcomp,15bar 825 K , (3) orDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 0.0056(Tcomp,15bar ) 4.68 if Tcomp,15bar 825K . (4) For the UC Berkeley CFR engine operating at 600 RPM with an intake temperature of 150°C, Tcomp,15bar is estimated to be 780K, yielding K=-0.312 using Eq. (4) (Kalghatgi, 2005). Because the OI was used to develop the HIrel, the temperature dependent constants for the HIrel, shown in Eq.(2), are also functions of Tcomp,15bar. For Tcomp,15bar = 780K, Shibata and Urushihara list values for the constants as follows (Shibata and Urushihara, 2007):α = - 0.487, β= -0.380, γ= -0.246, δ= -0.222, and ε=0.049. These constants were determined using a similar method as the K factor in the Octane Index. In addition to developing the relative HCCI Index, Shibata et al. (2005) suggested that low temperature heat release (LTHR) might correlate with auto-ignition better than high temperature heat release (HTHR). LTHR is defined as total heat release (Killingsworth, 2007) d from combustion at in-cylinder temperatures less than 1000K while HTHR is total heat released from combustion at in-cylinder temperatures greater than 1000K. In ACCEPTED MANUSCRIPT 7
  9. 9. ACCEPTED MANUSCRIPT their study, correlations between auto-ignition and LTHR were investigated by dividing LTHR by HTHR for each fuel, yielding a heat release ratio. In this paper, the net heat release per crank angle degree (dQ/dθ) was determined using the first law of thermodynamics (Heywood, 1988; Stone, 1999), dQ γ dV 1 dp = p + V (5) dθ γ 1 dθ γ 1 dθ where γ is the specific heat ratio, p is pressure, and V is volume. To avoid numericallyDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 differentiating the discrete pressure measurements and amplifying signal noise, Eq. (6) was be rewritten as, dQ 1 d(pV) dV = +p (6) dθ γ 1 dθ dθ and the cumulative net heat release, Qi, was computed as a finite sum instead of a continuous integral using (Killingsworth, 2007), i 1 Qi [pi Vi p 0 V0 ] p j ( V ) j, (7) 1 j 0 where i and j imply a discrete measurement of pressure and volume at a given crank angle degree. The specific heat ratio, γ, was assumed to be constant during compression and expansion. A linear fit between the compression γ and expansionγ was used to calculate dQ/dθ during combustion. Figure 1 shows the inflection points in the heat release rate that were used to distinguish between LTHR and HTHR. We assumed that LTHR began when the heat release rate was greater than zero and that HTHR ended when the heat release rate dropped below zero. Measurement Instrumentation ACCEPTED MANUSCRIPT 8
  10. 10. ACCEPTED MANUSCRIPT In-cylinder pressure was measured using a 6052B Kistler piezoelectric pressure transducer in conjunction with a 5044A Kistler charge amplifier and was recorded every 0.1 crank angle (CA) degree. The cylinder pressure transducer was mounted in the cylinder head. Intake pressure was measured using a 4045A5 Kistler piezoresistive pressure transducer in conjunction with a 4643 Kistler amplifier module. Crank angle position was determined using an optical encoder, while an electric motor, controlled by an ABB variable speed frequency drive, controlled the engine speed. A Motec M4 ECUDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 (Engine Control Unit) controlled injection timing, injection pulse width, and injection duty cycle. Before collecting data for each experiment, the engine was run until the coolant temperature reached 80°C and combustion became steady. A Horiba analyzer was used for measuring exhaust gases (CO, CO2, O2, unburned hydrocarbons (UHC), and nitrogen oxides (NOx)). For lean complete combustion, emissions measurements were used to deduce the normalized air-fuel ratio using, nc [O 2 ] 1 , (8) nH no [CO 2 ] nc 4 2 where nc is the number of carbon atoms in the fuel, nH is the number of hydrogen atoms in the fuel, nO is the number of oxygen atoms in the fuel, [O2] is the percent oxygen measured in the emissions, and [CO2] is the percent carbon dioxide measured in the emissions. The number of carbon, hydrogen, and oxygen atoms were estimated using the fuel composition. The uncertainty in the normalized air-fuel ratio is approximately± 0.05. EFFECTS OF FUEL COMPOSITION ON AUTO-IGNITION ACCEPTED MANUSCRIPT 9
  11. 11. ACCEPTED MANUSCRIPT The following results demonstrate the impact of fuel composition on auto-ignition in HCCI engines. First, auto-ignition timing, measured by CA50, of each fuel at various compression ratios is presented. Second, the Octane Index (OI) is compared with experimental data. Third, the relative HCCI Index (HIrel) is compared with experimental data. Fourth, correlations between fuel composition, auto-ignition and low temperature heat release (LTHR) are investigated. Auto-Ignition Timing (Ca50)Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 The effects of fuel composition on auto-ignition were first investigated by measuring the auto-ignition timing (CA50) of each fuel at various compression ratios. Figure 2 plots CA50 versus CR for the twenty fuels tested showing that fuel blends with similar ON do not always auto-ignite at the same CR, which is consistent with previous research (Liu et al., 2009). The uncertainty in CA50 and CR was calculated to be ±0.5 and ±0.1, respectively (Taylor, 1997). For example, tested fuels with ON~70 are: PRF70, S70, TRF70, E-PRF70, G2, and G1-H. As seen in Fig. 2, PRF70, S70, and G1-H auto-ignite at similar CR values. However, TRF70 auto-ignites half a CR higher than PRF70, E- PRF70 auto-ignites a full CR higher than PRF70, and G2 auto-ignites three CRs higher than PRF70. The results also suggest that ethanol inhibits auto-ignition more than toluene as S70 auto-ignites at the same CR as PRF70, while E-PRF70 auto-ignites a full CR higher than PRF70 and half a CR higher than TRF70. The results also show adding the same amount of ethanol, 10% by volume, to G1 (RON=87) and G2 (RON=70) does not have the same effect on auto-ignition. As shown in Fig. 2, G1-E2 (RON=90) auto-ignites about one CR higher than G1, while G2-E2 ACCEPTED MANUSCRIPT 10
  12. 12. ACCEPTED MANUSCRIPT (RON=78) auto-ignites three CRs higher than G2. Like ethanol, the naphthene, N1, affects auto-ignition of G2 more than G1; G2-N1 (RON=N/A) auto-ignites about half a CR higher than G2 and G1-N1 (RON=86) auto-ignites at about the same CR as G1. The Octane Index (Oi) Although the OI was developed for predicting anti-knock qualities of practical fuels in spark ignited engines, Kalghatgi (Kalghatgi, 2005) suggests that the OI can be used for predicting auto-ignition of fuels in an HCCI engine. For the CFR engine running at theDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 same inlet temperature, inlet pressure, and RPM, the compression ratio when CA50=6 deg ATDC is used for quantifying the fuel’s propensity of autoignition. This operating condition was chosen because data was successfully collected for all fuels when CA50=6 deg ATDC.Figure3 shows the relationship between OI and compression ratio when a CA50=6 deg ATDC for nineteen of the twenty fuels tested. The OI could not be calculated for G2-N1 because RON and MON were unavailable. The OI accurately predicts auto-ignition of the primary reference fuel (PRF) blends, agreeing well with previous results (Liu et al., 2009; Yao, Zheng and Liu, 2009). These results were expected because for PRF blends OI = ON. The OI poorly predicts auto-ignition of some fuels with the same ON. For example, the OI predicts S70, E-PRF70, and G2 will have similar auto-ignition characteristics; however, E-PRF70 auto-ignites almost one CR higher than S70 and G2 auto-ignites almost two CR higher than S70. Additionally, the OI poorly predicts auto-ignition of fuels containing naphthenes. The OI predicts G1-N1 (RON=86, MON=79) and G1-N2 (RON=87, MON=81) having similar auto-ignition characteristics, but the experimental results show G1-N2 auto-igniting one ACCEPTED MANUSCRIPT 11
  13. 13. ACCEPTED MANUSCRIPT CR higher than G1-N1. The OI also predicts G1-A2 (RON=91, MON=82) auto-igniting after G1-N2, but the experimental results show G1-N2 auto-igniting one CR higher than G1-A2. Although the OI correlates with the RON and MON, it is not sufficient for predicting auto-ignition of fuels with similar ON. The Relative HCCI Index (Hirel) The HIrel, introduced by Shibata and Urushihara (2007), is the first published research for predicting auto-ignition of fuels in an HCCI engine using the fuel composition and MON.Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 Like the OI, the HIrel predicts auto-ignition order of fuels; fuels with higher HIrel require higher CR for auto-ignition (i.e. more difficult to auto-ignite). Figure 4 shows the relationship between HIrel and CR when CA50=6 deg ATDC for nineteen of the twenty fuels tested. The HIrel could not be calculated for G2-N1 because MON was unavailable. The HIrel accurately predicts auto-ignition of some PRF blends, and some gasoline fuels blended with ethanol. However, the HIrel does not accurately predict ignition order of some fuels with similar ON. For example, PRF70, S70, G1-H, TRF70, E-PRF70, and G2 have the same HIrel, but experimental results show TRF70, E-PRF70, and G2 auto- igniting at different CRs than PRF70, S70, and G1-H and G2-E2 auto-igniting at different CR’s than PRF 75. The HIrel also poorly predicts auto-ignition of fuel blends containing different aromatics. The HIrel assumes that fuels containing different aromatic compounds at the same concentration and approximately same MON will have similar effects on auto-ignition, as all aromatics are grouped together in Eq. (2). Fig. 4 shows that different aromatics at the same concentration and approximately same MON can have different effects on auto- ACCEPTED MANUSCRIPT 12
  14. 14. ACCEPTED MANUSCRIPT ignition. For example, G1-A1 has a lower HIrel than G1-A2, but the experimental results show G1-A1 auto-igniting half a CR higher than G1-A2. Since naphthenes are not included in Eq. (2), and if their effects are assumed to be the same, the HIrel relation would predict G1-N1 and G1-N2 having similar effects on auto-ignition (Shibata and Urushihara, 2007). However, Fig. 4 shows G1-N1 auto-igniting one CR lower than G1- N2. It should be noted that temperature dependent constants used for computing HIrel were developed using the K factor in the OI. Therefore, the results from the HIrel wereDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 expected to be similar to the results from the OI. Low Temperature Heat Release Previous research (Shibata et al., 2005) suggests low temperature heat release (LTHR) may correlate with auto-ignition better than high temperature heat release (HTHR). Figures 5 and 6 show the dependence of the heat release ratio (the ratio of average LTHR to HTHR) on CR. For gasoline fuels, the heat release ratio decreases almost linearly as CR (when CA50=6 deg ATDC) increases from 9 to 15 (see Fig. 5). Gasoline fuels with the same ON show different heat release ratios and correlate well with CR. For example, G1-H auto-ignites almost 2 CRs lower than G2 and the heat release ratio predicts G1-H has about 3% less LTHR than G2. The heat release ratio also suggests gasoline fuels with more LTHR will auto-ignite at lower CR, agreeing with previous research (Shibata et al., 2005). For gasoline fuels auto-igniting at CRs greater than 15, no LTHR was detectable using our instrumentation. Figure 6 shows reference fuels with similar ON (PRF70, S70, TRF70, and E-PRF70) have similar amounts of LTHR, suggesting the reference fuels should auto-ignite at ACCEPTED MANUSCRIPT 13
  15. 15. ACCEPTED MANUSCRIPT similar CRs. However, these reference fuels do not auto-ignite at the same CR. For example, ethanol in E-PRF70 was expected to suppress LTHR. Instead, E-PRF70 shows similar amounts of LTHR as PRF70 while auto-igniting at the same CR as PRF75. The results suggest that the addition of Ethanol makes auto-ignition more difficult, but ethanol does not necessarily suppress LTHR. One possible explanation for E-PRF70 exhibiting the same LTHR as PRF70 is that the 31% n-heptane in E-PRF70 may promote more LTHR than ethanol suppresses. For fuels exhibiting decreasingly low amounts ofDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 LTHR, a water-cooled pressure transducers may provide better resolution (Sjoberg and Dec, 2003; Stone, 1999). Overall, the results show that LTHR correlates well with auto-ignition of gasoline blends exhibiting LTHR, but does not correlate well with reference fuel blends. This suggests that reference fuels for spark-ignited engines may not be appropriate reference fuels for HCCI engines. CONCLUSIONS In this paper, we investigated the impact of fuel composition on auto-ignition in HCCI engines in order to develop a future metric for predicting fuel performance in future HCCI engine technology. The following conclusions were derived: • For a fixed intake temperature, intake pressure, and equivalence ratio, fuels with the same Octane Number (ON) do not auto-ignite at similar compression ratios (CR). Additionally, the effect of ethanol (and naphthene) in delaying auto-ignition is dependent ACCEPTED MANUSCRIPT 14
  16. 16. ACCEPTED MANUSCRIPT on the gasoline blendstocks. The Octane Index and relative HCCI Index correlate well with auto-ignition of primary reference fuel but poorly predict auto-ignition of gasoline fuel blends containing naphthenes, aromatics, and ethanol. Low temperature heat release (LTHR) correlates well with auto-ignition for gasolineDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 fuels with measurable LTHR but does not correlate well for reference fuels. The results suggest that reference fuels may not be appropriate for describing fuel performance in HCCI engines. For fuels auto-igniting at CRs greater than 15, LTHR could not be detected. More than one metric may be required for predicting auto-ignition. For gasoline fuels that exhibit LTHR, LTHR better predicts auto-ignition order than Octane Index and the Relative HCCI Index. For fuels that do not exhibit LTHR, a different metric is needed. To further advance development of a future metric for predicting fuel performance in future HCCI engine technology, we recommend that more fuel blends containing linear amounts of toluene, ethanol, and various aromatics, by volume, should be explored to help identify reference fuels for a standard HCCI number. Additionally, different test conditions, such higher RPM and lower intake temperatures, should be explored further for the fuels used in this research. Trends established at different operating conditions could be used with trends found in this paper to establish a standard HCCI metric. ACCEPTED MANUSCRIPT 15
  17. 17. ACCEPTED MANUSCRIPT ACKNOWLEDGEMENTS Research conducted at the University of California, Berkeley was supported by the Chevron Corporation. The authors also wish to acknowledge the assistance of T. Dillstrom, A. Van Blarigan, and M. Wissink in conducting experimental measurements. ABBREVIATIONSDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 ATAC Active Thermo-Atmosphere Combustion ATDC After top dead center CA50 Crank angle at which 50% of heat has been released CAD Crank angle degree CFR Cooperative Fuel Research CIHC Compression ignition homogenous charge CR Compression ratio DI Direct Injection E-PRF Ethanol Reference Fuel ECU Engine control unit HCCI Homogenous Charge Compression Ignition HIrel, Relative HCCI Index HTHR High temperature heat release LTHR Low temperature heat release MON Motor Octane Number OI Octane Index ACCEPTED MANUSCRIPT 16
  18. 18. ACCEPTED MANUSCRIPT ON Octane Number PRF Primary Reference Fuel RON Research Octane Number SI Spark Ignition TRF Toluene Reference FuelDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 REFERENCES Anderson, J.E., Kramer, U., Mueller, S.A., and Wallington, T.J. 2010. Octane numbers of ethanol and methanol gasoline blends estimated from molar concentrations. Energy and Fuels, 24, 6576-6585. ASTM MON Standard 2011. D2700-11, Standard test method for motor octane number of spark-ignition engine fuel. ASTM International West Conshohocken, PA, DOI:10.1520/D2700-11, www.astm.org. ASTM RON Standard 2011. D2699-11, Standard test method for research octane number of spark-ignition engine fuel. ASTM International West Conshohocken, PA, DOI:10.1520/D2699-11, www.astm.org. Au, M.Y., Girard, J.W., Dibble, R.W., Flowers, D., Aceves, S.M., Martinez-Frias, J., Ray Smith, C.S., and Mass, U. 2001. 1.9-liter four cylinder HCCI engine operation with exhaust gas recirculation. SAE Technical Paper 2001-01-1894. Canova, M., Chiara, F., Cowgill, J., Midlam-Mohler, S., Guezennec, Y., and Rizzoni, G. 2007. Experimental Characterization of Mixed-Mode HCCI/DI Combustion on a Common Rail Diesel Engine. SAE Technical Paper 2007-24-0085. ACCEPTED MANUSCRIPT 17
  19. 19. ACCEPTED MANUSCRIPT Christensen, M., Johansson, B., and Einewall, P. 1997. Homogeneous charge compression ignition (HCCI) using isooctane, ethanol and natural gas - a comparison with spark-ignition operation. SAE Technical Paper 972874. Eng, J.A. 2002. Characterization of pressure waves in HCCI combustion. SAE Technical Paper 2002-01-2859. Eng, J., Leppard, W., and Sloane, T. 2003. The effect of di-tertiary butyl peroxide (DTBP) addition to gasoline on HCCI combustion. SAE Technical Paper 2003-01-3170.Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 Erlandsson, O. 2002. Early Swedish hot-bulb engines - Efficiency and performance compared to contemporary gasoline and diese engines. SAE Technical Paper 2002-01- 0115. Flowers, D., Aceves, S.M., Martinez-Frias, J., Smith, J.R., Au, M.Y., Girard, J.W., and Dibble, R.W. 2001. Operation of a four-cylinder 1.9L propane-fueled homogeneous charge compression ignition engine: Basic operating characteristics and cylinder-to- cylinder effects. SAE Technical Paper 2001-01-1895. Fuhs, A. 2008. Hybrid Vehicles and the Future of Personal Transport. Boca Raton: CRC Press. Gray, A.W., and Ryan, T.W. 1997. Homogeneous charge com- pression ignition (HCCI) of diesel fuel. SAE Technical Paper 971676. Helmantel, A., and Denbratt, I. 2004. HCCI operation of a passenger car common rail DI Diesel engine with early injection of Conventional Diesel fuel. SAE Technical Paper 2004-01-0935. Heywood, J.B. 1988. Internal Combustion Engine Fundamentals. McGraw-Hill, Inc. Hiltner, J., Agama, R., Mauss, F., Johansson, B., and Christensen, M. 2000. HCCI ACCEPTED MANUSCRIPT 18
  20. 20. ACCEPTED MANUSCRIPT operation with natural gas: Fuel composition implications. Proceedings of the 2000 ASME International Combustion Engine Fall Technical Conference., 35(2), 11-19. Kalghatgi, G.T. 2005. Auto-Ignition Quality of Practical Fuels and Implications for Fuel Requirements of Future SI and HCCI Engines. SAE Technical Paper 2005-01-0239. Killingsworth, N.J. 2007. HCCI Engine Control and Optimization. University of California, San Diego. Koopmans, L., Strom, H., Ludgren, S., Baklund, O., and Denbratt, I. 2003.Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 Demonstrating a SI-HCCI-SI Mode Change on a Volvo 5-Cylinder Electronic Valve Control Engine. SAE Technical Paper 2003-01-0753. Liu, H., Yao, M., Zhang, B. and Zheng, Z. 2009. Influence of fuel and operating conditions on combustion characteristics of a homogeneous charge compression ignition engine. Energy and Fuels, 23, 1422-1430. Morgan, N., Smallbone, A., Bhave, A., Kraft, M., Cracknell, R., and Kalghatgi, G. 2010. Mapping surrogate gasoline compositions into RON/MON space. Combustion and Flame, 157, 1122-1131. Najt, P.M., and Foster, D.E. 1983. Compression-ignited homogeneous charge combustion. SAE Technical Paper 830264. Noguchi, M., Tanaka, Y., Tanaka, T., and Takeuchi, Y. 1979. A study on gasoline engine combustion by observation of intermediate reactive products during combustion. SAE Technical Paper 790840. Oakley, A., Zhao, H., Ma, T., and Ladommatos, N. 2001. Dilution effects on the controlled auto-ignition (CAI) combustion of hydrocarbon and alcohol fuels. SAE Technical Paper 2001-01-3606. ACCEPTED MANUSCRIPT 19
  21. 21. ACCEPTED MANUSCRIPT Olsson, J.-O., Tunestal, P., Johansson, B., Fiveland, S., Rey Agama, M.W., and Assanis, D. 2002. Compression ratio influence on maximum load of a natural gas fueled HCCI engine. SAE Technical Paper 2002-01-0111. Onishi, S., Jo, S.H., Shoda, K., Jo, P.D., and Kato, S. 1979. Active thermo-atmosphere combustion (ATAC) - a new combustion process for internal combus- tion engines. SAE Technical Paper 790501. Shibata, G., Oyama, K., Urushihara, T., and Nakano, T. 2005. Correlation of LowDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 Temperature Heat Release With Fuel Composition and HCCI Engine Combustion. SAE Technical Paper 2005-01-0138. Shibata, G., and Urushihara, T. 2007. Auto-Ignition Characteristics of Hydrocarbons and Development of HCCI Fuel Index. SAE Technical Paper 2007-01-0220. Shudo, T., and Ono, Y. 2002. HCCI combustion of hydrogen, carbon monoxide and dimethyl ether. SAE Technical Paper 2002-01-0112. Sjoberg, M., and Dec, J.E. 2003. Combined Effects of Fuel-Type and Engine Speed on Intake Temperature Requirements and Completeness of Bulk-Gas Reactions for HCCI Combustion. SAE Technical Paper 2003-01-3173. Stanglmaier, R.H., Ryan, T.W., and Souder, J.S. 2001. HCCI operation of a dual-fuel natural gas engine for improved fuel efficiency and ultra-low NOx emissions at low to moderate engine loads. SAE Technical Paper 2001-01-1897. Stone, R. 1999. Introduction to internal combustion engines, 3rd ed., Warrendale: Society of Automotive Engineers, Inc. Taylor, J.R. 1997. An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements, 2nd ed., University Science Books Sausalito, California. ACCEPTED MANUSCRIPT 20
  22. 22. ACCEPTED MANUSCRIPT Thring, R.H. 1989. Homogeneous-charge compression ignition (HCCI) engines. SAE Technical Paper 892068. Wu, J., and Zhang, H. 2012. Analysis on Application of HCCI Technology for Hybrid Electric Vehicles. Applied Mechanics and Materials, 128-129, 803-806. Yao, M., Zheng, S., and Liu, H. 2009. Progress and recent trends in homogenous charge compression ignition (HCCI) engines. Progress in Energy and Combustion Science, 35, 398-437.Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 Zhang, Y., Xie, H., and Zhao, H. 2009. Investigation of SI-HCCI Hybrid Combustion and Control Strategies for Combustion Mode Switching in a Four- Stroke Gasoline Engine. Combustion Science and Technology, 181(5), 782-799. ACCEPTED MANUSCRIPT 21
  23. 23. ACCEPTED MANUSCRIPT Table 1. CFR engine specifications Displacement 0.616 L Stroke 114.3 mm Bore 82.8 mm Connecting Rod 254 mm Engine Speed 600 RPM Coolant Temperature 80°C ±1°CDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 Intake Pressure 1.035 bar Intake Temperature 150°C ±1°C ACCEPTED MANUSCRIPT 22
  24. 24. ACCEPTED MANUSCRIPT Table 2. Reference fuel blend compositions by volume percent with RON and MON Fuel Name % iso-ocatne % n-heptane % Toluene % Ethanol RON MON PRF 60 60 40 0 0 60 60 PRF 70 70 30 0 0 70 70 PRF 75 75 25 0 0 75 75 PRF 85 85 15 0 0 85 85 PRF 88 88 12 0 0 88 88Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 TRF 70* 0 46 54 0 70.5 63.5 S 70 64 31 5 0 70.5 69.6 E-PRF 70+ 64 31 0 5 69.5 68.6 n-heptane 0 100 0 0 0 0 * RON and MON were calculated using method described by Morgan et al. (2010). + RON and MON were calculated using bRON and bMON values from Anderson et al. (2010). RON and MON of remaining fuels were assumed. ACCEPTED MANUSCRIPT 23
  25. 25. ACCEPTED MANUSCRIPT Table 3. Base gasoline hydrocarbon class information (percent by volume) Fuel %N- %Iso- %Ole %Cycloparaffins %Arom RO MON Name Paraffins Paraffins fins atics N G1 14.2 44.9 5.2 9.8 25.9 87 80 G2 4.7 48.2 0.3 34.4 12.4 70 65Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 ACCEPTED MANUSCRIPT 24
  26. 26. ACCEPTED MANUSCRIPT Table 4. Gasoline fuel blend information Fuel Name Additive RON MON G1-H N-heptane 70b 65b G2-H N-heptane 60a 55a G1-E1 Ethanol 93a 84a G1-E2 Ethanol 90a 82a G2-E2 Ethanol 78a 68aDownloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 G1-A1 Toluene 91a 82a G1-A2 O-Xylene 91b 82b G1-N1 Methylcyclohexane 86b 79b G2-N1 Methylcyclohexane N/A N/A G1-N2 Cyclohexane 87b 81b “N/A” implies not available a RON or MON was estimated b RON or MON was provided by Chevron ACCEPTED MANUSCRIPT 25
  27. 27. ACCEPTED MANUSCRIPT Figure 1. Distinction between low temperature heat release (LTHR) from low temperature combustion and high temperature heat release (HTHR) from high temperature combustion.Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 ACCEPTED MANUSCRIPT 26
  28. 28. ACCEPTED MANUSCRIPT Figure 2. Auto-ignition in HCCI engines varies almost linearly with compression ratio. Fuels with the same octane number (ON), such as G2 and G1, do not auto-ignite at the same compression ratios. Error bars are suppressed for visibility. Error in CA50 is typically ± 0.5 of the shown value.Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 ACCEPTED MANUSCRIPT 27
  29. 29. ACCEPTED MANUSCRIPT Figure 3. The Octane Index poorly predicts auto-ignition fuels with similar Octane Number (ON) but shows an almost linear relationship (R2=0.90) with compression ratio for all fuel blends.Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 ACCEPTED MANUSCRIPT 28
  30. 30. ACCEPTED MANUSCRIPT Figure 4. HCCI index correlates well with primary reference fuel blends but poorly predicts auto-ignition of fuel blends containing ethanol, aromatics, or naphthenes.Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 ACCEPTED MANUSCRIPT 29
  31. 31. ACCEPTED MANUSCRIPT Figure 5. For gasoline fuels, the ratio of LTHR to HTHR shows an almost linear decrease with the compression ratio at a CA50=6 deg ATDC.Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 ACCEPTED MANUSCRIPT 30
  32. 32. ACCEPTED MANUSCRIPT Figure 6. Reference fuels with the same ON have similar amounts of LTHR even though they auto-ignite at different compression ratios. PRF blends decrease with compression ratio at a CA50=6 deg ATDC.Downloaded by [Universiti Teknologi Malaysia] at 20:55 11 January 2013 ACCEPTED MANUSCRIPT 31

×