DUAL-FUEL HCCI ENGINE EXPERIMENTS WITH PRIMARY REFERENCE FUELS Ali Aldawood 1,2 , Sebastian Mosbach 2 , Markus Kraft 2 , Amer Amer 1 1 Saudi Aramco 2 University of Cambridge Presented by: Gautam Kalghatgi, Saudi Aramco
Outline Introduction • Dual-fuel effects • Intake temperature effects • Summary •
Introduction Examine effects of fuel reactivity on HCCI operating limits, • and overall feasibility of the dual-approach for extending HCCI operating range Intake air temperature effects on engine operation stability • and lower load limit, and feasibility of combining intake air heating with dual-fuel approach
Experimental Detail Single-cylinder engine – 0.5 L PFI – • • PRF (iso-octane and n-heptane) fuels of 40, 60, 80 ON Intake pressure and back pressure fixed at 1.5 bar abs. • • Two intake temperatures - 75˚C and 90˚C Three different speeds, 1200, 1500 and 1800 RPM • Different equivalence ratios • • Pressure data for 300 consecutive cycles Emissions – averaged over 60 s at 0.1s interval •
Pressure Trace and Heat Release Heat release curves of • 90 90 1500 rpm Φ =0.323 1500 rpm PRF40 exhibit two-stage PRF80 80 80 PRF40 0.290 Φ =0.358 Cylinder Pressure (bar) 0.346 ignition characteristics 0.258 70 70 0.336 0.230 60 60 0.324 0.195 50 50 First-stage heat release • 40 40 becomes weaker as the 30 30 iso-octane ratio 20 20 -20 -10 0 10 20 30 -20 -10 0 10 20 30 increases 120 120 Φ =0.323 100 100 Φ =0.358 Load range becomes • 80 80 0.346 HRR (J/deg) 0.290 narrower and sensitivity 60 60 0.336 of pressure history to 0.258 0.324 40 40 0.230 equivalence ratio 20 20 0.195 becomes stronger as iso- 0 0 octane ratio increases -20 -10 0 10 20 30 -20 -10 0 10 20 30 CAD (deg) CAD (deg)
15 PRF40 1200 rpm PRF60 10 PRF80 CA50 (ATDC) Misfire 5 limit 0 Combustion Phasing Knock -5 limit -10 Misfire and knock limits are set • 0.1 0.15 0.2 0.25 0.3 0.35 0.4 following the definitions of 15 1500 rpm HLL (7 MPa/ms) and LLL 10 Misfire CA50 (ATDC) (5.0% IMEP COV) limit 5 0 • Combustion phasing advances Knock limit -5 (almost linearly) with increasing -10 load until reaching the knock 0.1 0.15 0.2 0.25 0.3 0.35 0.4 limit – Not constant 15 1800 rpm 10 The operating window becomes • CA50 (ATDC) Misfire 5 narrower with increasing speed limit Knock 0 limit -5 -10 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Φ
Effects on Load Range and Efficiency • Decreasing fuel reactivity 1200rpm 1500rpm 1800rpm 8 8 8 expands upper load limit PRF40 Gross IMEP (bar) PRF60 6 6 6 and the plateau where PRF80 4 4 4 ISFC is low and indicated 2 2 2 efficiency is high 0 0 0 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 500 500 500 • This effect becomes more Gross ISFC (g/kW.h) noticeable as engine 400 400 400 speed increases 300 300 300 200 200 200 Maximum IMEPg of 7.2 • 100 100 100 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 bar, maximum indicated 0.5 0.5 0.5 η Indicated Efficiency, efficiency of 44%, and 0.4 0.4 0.4 minimum ISFCg of 185.5 0.3 0.3 0.3 0.2 0.2 0.2 g/kW .h are obtained with 0.1 0.1 0.1 PRF80 at 1800 RPM 0 0 0 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 Φ Φ Φ
High and Low Load Limits 1200rpm 1200rpm 0.5 8 Increasing fuel reactivity • Max. PRR (MPa/ms) PRF40 0.4 6 PRF60 increases engine stability at low IMEP CoV PRF80 0.3 load but makes the engine more 4 0.2 susceptible to knock at higher 2 0.1 loads 0 0 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 1500rpm 1500rpm Boundaries of efficiency plateau • 0.3 8 Max. PRR (MPa/ms) generally correspond to MPRR 6 IMEP CoV 0.2 of aprox. 7 MPa/ms on high load 4 side and 3.5% IMEP COV in low 0.1 2 load side 0 0 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 Variations in MPRR increase • 1800rpm 1800rpm 0.8 8 sharply with increasing speed Max. PRR (MPa/ms) 0.6 6 IMEP CoV 0.4 4 0.2 2 0 0 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 Φ Φ
Operating Envelopes for Different Fuels Clear potential for variable reactivity • approach Operating envelopes shrink with • decreasing fuel reactivity and increasing engine speed More reactive fuels allow engine to • operate with leaner mixtures Fuel effects are not linear with octane • number
Fuel Effects on Operating Limits LLL and HLL are less sensitive to • changes in octane rating between 40 and 60 than between 60 and 80 This means that decreasing fuel • reactivity below certain limit does not help in controlling load or extending LLL • This nonlinear effect necessitates use of other combustion control means to complement dual fuel approach during low load operation
Intake Temperature Effects 1200 rpm 1200 rpm 0.25 8 PRF60-IAT=75 o C Max. PRR (MPa/ms) Increasing intake • 0.2 PRF80-IAT=75 o C 6 IMEP CoV PRF60-IAT=90 o C temperature improved the 0.15 PRF80-IAT=90 o C 4 0.1 engine operating stability at 2 0.05 low and intermediate load 0 0 but increased pressure rise 2 4 6 8 2 4 6 8 rate at high load. 0.25 8 1500 rpm 1500 rpm Max. PRR (MPa/ms) 0.2 6 IMEP CoV 0.15 Operating envelope shifts at • 4 0.1 each speed to lower load side 2 0.05 and operation becomes more 0 0 2 4 6 8 2 4 6 8 stable in general 0.25 8 1800 rpm 1800 rpm Max. PRR (MPa/ms) 0.2 6 IMEP CoV 0.15 4 0.1 2 0.05 0 0 2 4 6 8 2 4 6 8 Gross IMEP (bar) Gross IMEP (bar)
Intake Temperature Effects 4 Increasing intake x 10 • 0.5 PRF60-IAT=75 o C 2 PRF60 - IAT=75 o C 1500rpm 1500 rpm temperature caused a PRF80-IAT=75 o C PRF80 - IAT=75 o C 0.4 PRF60-IAT=90 o C 1.5 PRF60 - IAT=90 o C HC (ppm) slight decrease in PRF80-IAT=90 o C PRF80 - IAT=90 o C Φ 0.3 1 efficiency at higher 0.2 0.5 loads 0.1 0 0 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 500 2 Increasing intake Gross ISFC (g/kW.h) • 400 1.5 temperature resulted CO(%) 300 1 in consistent reduction 200 0.5 in CO emissions 100 0 0 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 0.5 8 HC emissions η • Indicated Efficiency, 0.4 6 decreased at low load NOx (ppm) 0.3 4 0.2 2 0.1 0 0 0 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 Gross IMEP (bar) Gross IMEP (bar)
20 PRF60-IAT=75 o C 1200 rpm PRF80-IAT=75 o C 15 PRF60-IAT=90 o C CA50 (ATDC) PRF80-IAT=90 o C 10 5 Combustion Phasing 0 -5 Increasing intake temperature • 1 2 3 4 5 6 7 8 caused a slight advance in 20 1500 rpm combustion phasing, especially 15 CA50 (ATDC) with PRF60 10 5 • This may explain the slight decrease in efficiency at the 0 higher load -5 1 2 3 4 5 6 7 8 20 1800 rpm 15 CA50 (ATDC) 10 5 0 -5 1 2 3 4 5 6 7 8 Gross IMEP (bar)
Intake Temperature Effects Increasing intake • temperature extended LLL but slightly decreased HLL. Operating envelope, therefore, was expanded more towards the low load region Increasing intake • temperature from 75 o C to 90 o C resulted in an operating range equivalent to that obtained by decreasing the PRF octane rating from 60 to 40.
Summary • Decreasing fuel reactivity results in narrower operating window but expands high load limit and shifts operation towards higher equivalence ratio. These effects became more prominent as speed increased • Increasing fuel reactivity becomes increasingly less effective in controlling HCCI combustion as engine load decreases. This nonlinear effect renders reactivity-base control not effective for extending low load limit Increasing intake temperature extended low load limit and enabled a • more stable operation in general • Increasing intake temperature resulted in some positive, but generally not significant, effects on engine performance and exhaust emissions. Most noticeable effect was the consistent reduction of CO emissions within the low to intermediate load region
Back-up slides
Operating Window Max. PRR (MPa/ms) 8 7.0 IAT = 75 o C 6 1500 rpm 4 High PRF60 load 2 • Boundaries of efficiency plateau limit 0 0.1 0.15 0.2 0.25 0.3 0.35 were generally found to 0.3 correspond to an MPRR of about IMEP CoV Low 0.2 load 7 MPa/ms on high load side and limit 0.1 0.05 3.5% IMEP COV in low load side 0 0.1 0.15 0.2 0.25 0.3 0.35 η Indicated Efficiency, • Clear correlation between 0.4 0.35 Operating range indicted efficiency and CO and 0.2 HC emissions 0 0.1 0.15 0.2 0.25 0.3 0.35 2 • HLL is set at 7 MPa/ms and LLL CO (%) 1 is set at 5% IMEP COV , accepting some penalty in thermal 0 0.1 0.15 0.2 0.25 0.3 0.35 efficiency and CO emissions 4 x 10 2 HC (ppm) 1 0 0.1 0.15 0.2 0.25 0.3 0.35 Φ
Engine Test Cell Displacement 499 cm 3 Stroke 90 mm Bore 84 mm Connecting rod 159 mm Compression ratio 12:1 Fuel delivery system PFI
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