1. A Review by: Ritwik Athalye April 28th, 2015
An investigation on RCCI combustion in a heavy duty diesel engine using in-cylinder blending of diesel and gasoline fuels Jesús Benajes, Santiago Molina, Antonio García, Eduardo Belarte, Michel Vanvolsem
A Review by: Ritwik Athalye
April 28th, 2015

2. Introduction and Motivation :
Development of new combustion modes with the aim of reducing fuel consumption and emissions in IC Engines.
HCCI & PCCI: High efficiency can be achieved along with reduction in NOx and Soot using leaner mixture & medium/high levels of EGR to provide Low Temperature Combustion.
Practical issues: achieving appropriate combustion phasing and cycle-to-cycle control
RCCI overcomes these drawbacks by controlling combustion with the help of fuel reactivity stratification inside the combustion chamber
The automotive industry is nowadays focusing its efforts on development of new combustion modes as well as optimizing the existing technology with the aim of reducing fuel consumption and emissions
Some of the LTC Strategies : HCCI, PCCI.
Additional issues: Noise, high load operation
RCCI : dual fuel PCCI – fuel reactivity control!

3. Introduction and Motivation :
Goals of the paper -
To improve the fundamental understanding of RCCI Combustion phenomenon.
To analyze and describe the mixing and combustion processes as well as pollutant emissions using diesel (high reactivity) & gasoline (low reactivity) in-cylinder blending.
To observe the effect of varying fuel-blend and diesel injection timing on combustion and emissions.
Understanding RCCI : Mixing and combustion processes, emissions
Vary engine operating conditions – fuel blend, Diesel SoI,

4. Experimental Setup :
1.8 L Single Cylinder Engine with PFI of Gasoline and DI of Diesel
All experiments run at low (25%) load and 1200 rpm
- Schematic of the engine test cell
- All experiments run at low load (25% load) & 1200 rpm (A25 mode of the European Stationary Cycle)
- More over, except for the first parametric study, the total injected fuel mass, the intake pressure and EGR Rate were kept constant providing a global equivalence ratio of 0.7 and intake O2 mass fraction at IVC of 15.5%.

5. Description of Parametric Studies:
Effects of adding port-fuel injected gasoline to neat diesel on combustion
Direct injected diesel fuel amount was kept constant & total amount of fuel was increased by adding gasoline by PFI
Effects of varying the in-cylinder fuel blending ratio on RCCI combustion
Starting from neat diesel combustion, amount of diesel fuel injected was reduced up to 10% and amount of gasoline was increased keeping the total amount of fuel injected constant
Effects of varying injection timing on RCCI combustion
Injection timing of high reactivity fuel (Diesel) was varied
Three parametric studies
Effects on mixing/ combustion and emissions

6. I. Adding PFI Gasoline to DI Diesel:
Operating Conditions
Effect on Heat Release Rate
Stages of Combustion:  Cool flame reactions promoted by diesel injection  Main energy release (premixed burning) by auto-ignition of high reactivity zones Late combustion stage due to multiple flame propagation through low reactivity zones
More fuel input -> therefore, higher peak of HRR.
Three stages of combustion
- With more & more premixed gasoline, the late combustion stage gets enhanced, since the low reactivity regions burn during late combustion stage.

7. II. Varying In-cylinder Fuel Blending Ratio:
Operating Conditions
Effect on Heat Release Rate
 As diesel/gasoline ratio is reduced from 100/0% to 50/50%, ignition delay increases due to lowering of global fuel reactivity.  Premixed stage shows higher peaks of HRR since diesel has more time to entrain air & gasoline.  As diesel/gasoline ratio is reduced further to 25/75%, the two staged combustion shows a squared shape and the peak HRR is reduced.
3. Lower amount of high reactivity fuel (less diesel)  lower 1st peak and higher 2nd peak (due to enhancement of late combustion)
- Desirable combustion phasing
 With diesel/gasoline ratio of 10/90%, combustion is highly worsened. Diesel injection event is too short and the energy given out is not enough to onset multiple propagation flames.

8. II. Varying In-cylinder Fuel Blending Ratio:
Effect on Engine Emissions
 As diesel/gasoline ratio is reduced from 100/0% to 50/50% and further, soot emissions are strongly reduced due to longer ignition delay and increase of low reactivity fuel amount.  However, CO & UHC increase due to worsening of oxidation.
 For diesel/gasoline ratio of 25/75%, there is a noticeable increase in NOx. This is due to extended duration of peak HRR and thus, higher adiabatic flame temp.  For 10% diesel case, high levels of CO & UHC are due to worsening of combustion efficiency.
Longer ign. Delay  more mixing time  less soot; also, low reactivity fuel has shorter fuel molecules
Crevice effects increase as low reactivity fuel amount increases
Extended duration of peak HRR  higher temperature  more Nox
Low Combustion efficiency + crevice effects

9. III. Varying Diesel Injection Timing:
Operating Conditions
Effect on Heat Release Rate (25d/75g%)
 As diesel injection is advanced, the ignition delay is increased and the combustion duration is decreased.  This is because the local equivalence ratio stratification is reduced due to longer time for mixing.  As a result, the 2nd stage of heat release gets enhanced and HRR profile tends to have a squared shape.
Longer time for mixing  local equivalence ratio stratification is reduced  ign. Delay increases
With advancing SoI, 1st stage decreases & 2nd stage enhances.

10. III. Varying Diesel Injection Timing:
Effect on Engine Emissions
 As the diesel injection timing is advanced, NOx and Soot increase while CO & UHC are reduced.  This is because the peak of premixed heat release and hence, the adiabatic temperature increases. Also, the local equivalence ratios are richer.
 Interestingly, with further advancing of SOI from -24ᵒ aTDC, NOx is lowered while CO & UHC are slightly increased. This is because of leaner equivalence ratios, lower peak of heat release and lower max. adiabatic flame temperatures.
With advancing SoI, higher NOx because higher temperature residence time
Higher (blue) UHC because higher low reac. Fuel (crevice effects)
With more mixing time, overall equivalence ratios are leaner + lower peak of HRR  lower temperature  lower NOx

11. Conclusions:
RCCI is a staged combustion process controlled by the mixture reactivity stratification.
As in-cylinder fuel blend ratio is varied towards lower global reactivity blend (~25d/75g%), the ignition delay gets longer, combustion duration is shortened, premixed combustion gets lowered and a square shaped HRR is observed.
As diesel injection timing is advanced, fuel mixture gets better stratified and less zones of low local reactivity exist in cylinder.
Important reduction in Soot and NOx, while increase in CO & UHC (mainly due to crevice effects) was observed as compared to Conventional Diesel Combustion( CDC)
“RCCI – a promising way to meet future emissions regulations, without expensive after-treatment systems! “

12. Thank You!