3. Gasoline-CNG mixtures in RCCI combustion system

The gasoline-CNG mixtures performance and combustion in RCCI combustion system from both methods are elaborated in this section. It explained the parameters affecting the combustion of low-reactive fuels and method in controlling the combustion process.

## 3.1. Gasoline-CNG combustion behavior in RCCI combustion-based engine

The degree of stratification of CNG in the total mixture was found to have significant effects on the maximum load in terms of the IMEP attainable and φTotal. The degree of stratification is determined by the injection timing with 300 BTDC representing the homogeneous mixture, while 120 BTDC represents the stratified mixture. The 300 BTDC has a very early injection timing, and the fuel is injected during intake valve is open. It is, therefore, the fuel that has sufficient time to be completely mixed with air and create a homogeneous mixture. While on the other hand, for 120 BTDC, the fuel is injected after intake valve closed and mixing time between fuel and air is very short and does not allow a complete mixing to take place.

Figure 11 shows that at 300 and 240 BTDC injection higher total equivalence ratios could be operated. But with 180 and 120 BTDC, the maximum operable φTotal was limited with reduced IMEP at a given φTotal when compared to the 300 and 240 BTDC cases.

The IMEP results show agreement with investigation from Genchi G and Pipitone E [22] where the increased composition of CNG produces higher IMEP. With the highest degree of stratification, although the maximum load was limited, there was no significant drop in the IMEP and the trend was similar to 300 and 240 BTDC conditions. The corresponding values of indicated thermal efficiencies are shown in Figure 12. The maximum load was observed to be limited by knocking when CNG was injected at 300 BTDC, and for the other cases, increasing CNG injection rate led to unstable operation or misfire.

Figure 11. Effect of degree of stratification of CNG on IMEP. (K—limited by knocking; mf—limited by misfire).

Figure 10. Injector control system interface.

Figure 9. Schematic diagram of the control system and data acquisition.

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From Figure 13, it can be seen that the ignition timing could be altered by changing the timing of injection of CNG at a given load. The ignition timing was determined by identifying the start of heat released rate and mass fraction burned derived from the pressure data where the 0% points before the continuous propagation of the mass fraction burned is determined as the start of ignition of the analyzed combustion cycles.

When the rate of CNG injection was increased, the ignition timing was delayed due to the higher octane number of CNG. Also, higher degrees of stratification resulted in higher increments in the delay of ignition timing as the CNG injection rate was increased. The slope of the curves was steeper when the injection timing was delayed. For a given increase in the CNG injection rate, the increase in delay in ignition timing was higher when the degree of stratification was increased. That is both the injection rate and the degree of stratification of CNG had significant effects on the ignition timing when operated with φg = 0.20. However, the maximum total equivalence

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It was found that the combustion duration was reduced when CNG injection rate was increased at 300, 240, and 80 BTDC. When CNG was injected at 180 and 120 BTDC, the combustion duration was marginally affected and it initially decreased up to certain values of

Figures 15–18 show the rate of heat release and pressure rise at various injection timings. Increasing the rate of CNG injection at 300 BTDC was limited by knocking as shown in Figure 14. But with later injection timings, with φg = 0.20, any increase in CNG injection rate resulted in a delayed autoignition and reduced peak pressure. Therefore, increasing CNG injection rate beyond certain levels led to misfire or no fire, thereby defining the maximum

As shown in Figure 15, when CNG injection rate was increased, it resulted in delayed ignition timing. Up to φTotal = 0.33, the resultant peak pressure increased, and with a further increase in CNG injection rate, it decreased. Also, above φ Total = 0.33, the delay in ignition timing was more significant and resulted in decreased peak pressures. As will be discussed later in this section, combustion efficiency of both the fuels increased and CH4 emissions decreased with

ratio was less than that obtained with CNG injection at 300 and 240 BTDC.

Figure 14. Effect of degree of CNG stratification of CNG on the combustion duration.

an increase in φTotal above 0.33 as shown in Figures 23 and 29.

CNG injection rate and then it increased again.

load limit.

Figure 12. Effect degree of CNG stratification on the indicated thermal efficiency.

Figure 13. Effect of degree of CNG stratification on ignition timing.

Figure 14. Effect of degree of CNG stratification of CNG on the combustion duration.

From Figure 13, it can be seen that the ignition timing could be altered by changing the timing of injection of CNG at a given load. The ignition timing was determined by identifying the start of heat released rate and mass fraction burned derived from the pressure data where the 0% points before the continuous propagation of the mass fraction burned is determined as

the start of ignition of the analyzed combustion cycles.

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Figure 12. Effect degree of CNG stratification on the indicated thermal efficiency.

Figure 13. Effect of degree of CNG stratification on ignition timing.

When the rate of CNG injection was increased, the ignition timing was delayed due to the higher octane number of CNG. Also, higher degrees of stratification resulted in higher increments in the delay of ignition timing as the CNG injection rate was increased. The slope of the curves was steeper when the injection timing was delayed. For a given increase in the CNG injection rate, the increase in delay in ignition timing was higher when the degree of stratification was increased. That is both the injection rate and the degree of stratification of CNG had significant effects on the ignition timing when operated with φg = 0.20. However, the maximum total equivalence ratio was less than that obtained with CNG injection at 300 and 240 BTDC.

It was found that the combustion duration was reduced when CNG injection rate was increased at 300, 240, and 80 BTDC. When CNG was injected at 180 and 120 BTDC, the combustion duration was marginally affected and it initially decreased up to certain values of CNG injection rate and then it increased again.

Figures 15–18 show the rate of heat release and pressure rise at various injection timings. Increasing the rate of CNG injection at 300 BTDC was limited by knocking as shown in Figure 14. But with later injection timings, with φg = 0.20, any increase in CNG injection rate resulted in a delayed autoignition and reduced peak pressure. Therefore, increasing CNG injection rate beyond certain levels led to misfire or no fire, thereby defining the maximum load limit.

As shown in Figure 15, when CNG injection rate was increased, it resulted in delayed ignition timing. Up to φTotal = 0.33, the resultant peak pressure increased, and with a further increase in CNG injection rate, it decreased. Also, above φ Total = 0.33, the delay in ignition timing was more significant and resulted in decreased peak pressures. As will be discussed later in this section, combustion efficiency of both the fuels increased and CH4 emissions decreased with an increase in φTotal above 0.33 as shown in Figures 23 and 29.

Figure 15. Pressure history and heat release rates with CNG injection at 240 BTDC.

Therefore, it can be concluded that, above φTotal = 0.33, the peak pressure was reduced due to delayed ignition, and the combustion was more complete with increase in injection rate at 240 BTDC. That is, increasing φg above 0.33 resulted in reduced peak pressures without a decrease in thermal efficiency as shown in Figure 12. Heat release rates increased with an increase in CNG injection rate up to φTotal = 0.40 above which it reduced again. Above φTotal = 0.42, increasing CNG injection rate resulted in misfire or no fire, and both gasoline and CNG combustion was quenched.

emissions as shown in Figures 23 and 29. This suggests that the degree of stratification created at 180 BTDC injection results in deterioration in combustion and leads to decrease in thermal efficiency as shown in Figure 12. Similar, trends were observed with CNG injection at 120

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When CNG injection was retarded to 80 BTDC, increase in injection rate resulted in significant delay in ignition; however, there was less noticeable effect on peak pressures up to φTotal = 0.28. Increasing φTotal above resulted in a more significant delay in ignition and peak pressure, and heat release rates increased. Thermal efficiency and combustion efficiency increased primarily due to remarkable increase in completeness of CNG combustion as suggested by CH4 emissions

As shown in Figure 19, increasing CNG injection rate at 240 BTDC resulted in delayed ignition. At φTotal = 0.28 and 0.33, there was a slight increase in burning rate at the last stage of combustion compared to combustion with pure gasoline. At 180 and 120 BTDC, there was no significant effect on the burning rate of the fuels due to increase in CNG injection rate, but it caused a significant delay in ignition as shown in Figures 20 and 21. Similar results were obtained with CNG injection at 80 BTDC; however, at φTotal = 0.28 and 0.33, the combustion

was slower at the initial stages and was faster at latter stages as shown in Figure 22.

BTDC when φTotal was increased above 0.24 as shown in Figure 16.

Figure 16. Pressure history and heat release rates with CNG injection at 120 BTDC.

as shown in Figure 29.

With CNG injection at 180 BTDC, increase in CNG injection rate resulted in a more significant delay in ignition timing. There was a marginal increase in peak pressure when φTotal was increased to 0.26 above which it reduced again. Thermal efficiency and combustion efficiency increased primarily due to the remarkable increase in the completeness of CNG combustion as suggested by CH4 emissions as shown in Figure 29. Heat release rate increased with an increase in CNG injection rate as shown in Figure 17. However, increasing CNG injection rate above φTotal = 0.26 resulted in decreased overall combustion efficiency and high CH4

Figure 16. Pressure history and heat release rates with CNG injection at 120 BTDC.

Therefore, it can be concluded that, above φTotal = 0.33, the peak pressure was reduced due to delayed ignition, and the combustion was more complete with increase in injection rate at 240 BTDC. That is, increasing φg above 0.33 resulted in reduced peak pressures without a decrease in thermal efficiency as shown in Figure 12. Heat release rates increased with an increase in CNG injection rate up to φTotal = 0.40 above which it reduced again. Above φTotal = 0.42, increasing CNG injection rate resulted in misfire or no fire, and both gasoline and CNG

Figure 15. Pressure history and heat release rates with CNG injection at 240 BTDC.

With CNG injection at 180 BTDC, increase in CNG injection rate resulted in a more significant delay in ignition timing. There was a marginal increase in peak pressure when φTotal was increased to 0.26 above which it reduced again. Thermal efficiency and combustion efficiency increased primarily due to the remarkable increase in the completeness of CNG combustion as suggested by CH4 emissions as shown in Figure 29. Heat release rate increased with an increase in CNG injection rate as shown in Figure 17. However, increasing CNG injection rate above φTotal = 0.26 resulted in decreased overall combustion efficiency and high CH4

combustion was quenched.

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emissions as shown in Figures 23 and 29. This suggests that the degree of stratification created at 180 BTDC injection results in deterioration in combustion and leads to decrease in thermal efficiency as shown in Figure 12. Similar, trends were observed with CNG injection at 120 BTDC when φTotal was increased above 0.24 as shown in Figure 16.

When CNG injection was retarded to 80 BTDC, increase in injection rate resulted in significant delay in ignition; however, there was less noticeable effect on peak pressures up to φTotal = 0.28. Increasing φTotal above resulted in a more significant delay in ignition and peak pressure, and heat release rates increased. Thermal efficiency and combustion efficiency increased primarily due to remarkable increase in completeness of CNG combustion as suggested by CH4 emissions as shown in Figure 29.

As shown in Figure 19, increasing CNG injection rate at 240 BTDC resulted in delayed ignition. At φTotal = 0.28 and 0.33, there was a slight increase in burning rate at the last stage of combustion compared to combustion with pure gasoline. At 180 and 120 BTDC, there was no significant effect on the burning rate of the fuels due to increase in CNG injection rate, but it caused a significant delay in ignition as shown in Figures 20 and 21. Similar results were obtained with CNG injection at 80 BTDC; however, at φTotal = 0.28 and 0.33, the combustion was slower at the initial stages and was faster at latter stages as shown in Figure 22.

again. That is, up to a certain value of CNG injection rate, CNG reduced the combustion

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temperature and led to formation of higher amounts of NO2.

Figure 18. Pressure history and heat release rates with CNG injection at 80 BTDC.

Figure 19. Mass fractions burned with CNG injection at 240 BTDC.

Figure 17. Pressure history and heat release rates with CNG injection at 180 BTDC.

As shown in Figure 23, with an increase in φTotal by CNG injection at 300, 240, and 80 BTDC, combustion efficiency increased. The highest increment was obtained with CNG injection at 80 BTDC for a given increase in φTotal due to mixture stratification. However, CNG injection at 180 and 120 BTDC, combustion efficiency increased initially but decreased again and was below 80% for all φTotal.

The exhaust gas temperature was observed to increase as the CNG injection rate was increased as shown in Figure 24. The increase in exhaust gas temperature with increasing CNG injection rates at 180 and 120 BTDC was less than that observed with increasing CNG injection rates at 300, 240, and 80 BTDC. When the fuels were homogeneously mixed, it resulted in higher exhaust gas temperatures due to rapid burning. Similarly, when CNG was highly stratified, it also led to higher exhaust gas temperatures.

Figure 25 shows the indicated specific NOx (ISNOx) emissions. The NOx emissions were marginally affected and were around the same levels for all test conditions. However, different trends were observed at different injection timings and CNG injection rates.

Increasing the CNG injection rate resulted in a drastic increase in the NO2/NOx ratio up to a certain point and then it decreased. As shown in Figure 26, the ratio of NO2/NOx almost doubled when the CNG injection rate was increased to around φTotal = 0.33 before decreasing again. That is, up to a certain value of CNG injection rate, CNG reduced the combustion temperature and led to formation of higher amounts of NO2.

Figure 18. Pressure history and heat release rates with CNG injection at 80 BTDC.

As shown in Figure 23, with an increase in φTotal by CNG injection at 300, 240, and 80 BTDC, combustion efficiency increased. The highest increment was obtained with CNG injection at 80 BTDC for a given increase in φTotal due to mixture stratification. However, CNG injection at 180 and 120 BTDC, combustion efficiency increased initially but decreased again and was

The exhaust gas temperature was observed to increase as the CNG injection rate was increased as shown in Figure 24. The increase in exhaust gas temperature with increasing CNG injection rates at 180 and 120 BTDC was less than that observed with increasing CNG injection rates at 300, 240, and 80 BTDC. When the fuels were homogeneously mixed, it resulted in higher exhaust gas temperatures due to rapid burning. Similarly, when CNG was highly stratified, it

Figure 25 shows the indicated specific NOx (ISNOx) emissions. The NOx emissions were marginally affected and were around the same levels for all test conditions. However, different

Increasing the CNG injection rate resulted in a drastic increase in the NO2/NOx ratio up to a certain point and then it decreased. As shown in Figure 26, the ratio of NO2/NOx almost doubled when the CNG injection rate was increased to around φTotal = 0.33 before decreasing

trends were observed at different injection timings and CNG injection rates.

Figure 17. Pressure history and heat release rates with CNG injection at 180 BTDC.

below 80% for all φTotal.

68 Improvement Trends for Internal Combustion Engines

also led to higher exhaust gas temperatures.

Figure 19. Mass fractions burned with CNG injection at 240 BTDC.

Figure 20. Mass fractions burned with CNG injection at 180 BTDC.

Figure 21. Mass fractions burned with CNG injection at 120 BTDC.

The indicated specific CO (ISCO) emissions were reduced significantly as the mixture was enriched with CNG by direct injection at all injection timings as shown in Figure 27. However, the reduction obtained was the highest when CNG was injected at 300 and 240 BTDC. Any increase in CNG injection rate at later injection timings resulted in less reductions in CO emissions. The lowest reduction was obtained at the injection timing of 80 BTDC, as the high degree of stratification of CNG limited the availability and distribution of oxygen and temperature differences in the CNG and air particles.

injection at 80 BTDC. Higher degrees of stratification of CNG resulted in more complete

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Figure 29 shows the mass ratio of flow rates of CH4 in the exhaust emissions and mass flow rate of CNG injected into the cylinder. At a given constant gasoline equivalence ratio of φg = 0.20, CNG direct injection at 80 BTDC resulted in the least emission of CH4. Therefore, the combustion of CNG was more complete when it was stratified. CNG injection at 300 and 240 BTDC resulted in moderate levels of CH4 emissions, and highest values were obtained with CNG injection at 180 BTDC. This was due to the turbulence created and mixing condi-

tions in the cylinder when the piston changed its direction at 180 BTDC.

Figure 22. Mass fractions burned with CNG injection at 80 BTDC.

Figure 23. Effect of degree of stratification on combustion efficiency.

combustion.

The HC emissions were found to be significantly affected by the degree of stratification of CNG as shown in Figure 28. The highest reduction in HC emissions was obtained with CNG Reactivity Controlled Compression Ignition (RCCI) of Gasoline-CNG Mixtures http://dx.doi.org/10.5772/intechopen.72880 71

Figure 22. Mass fractions burned with CNG injection at 80 BTDC.

Figure 23. Effect of degree of stratification on combustion efficiency.

The indicated specific CO (ISCO) emissions were reduced significantly as the mixture was enriched with CNG by direct injection at all injection timings as shown in Figure 27. However, the reduction obtained was the highest when CNG was injected at 300 and 240 BTDC. Any increase in CNG injection rate at later injection timings resulted in less reductions in CO emissions. The lowest reduction was obtained at the injection timing of 80 BTDC, as the high degree of stratification of CNG limited the availability and distribution of oxygen and temper-

The HC emissions were found to be significantly affected by the degree of stratification of CNG as shown in Figure 28. The highest reduction in HC emissions was obtained with CNG

ature differences in the CNG and air particles.

Figure 21. Mass fractions burned with CNG injection at 120 BTDC.

Figure 20. Mass fractions burned with CNG injection at 180 BTDC.

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injection at 80 BTDC. Higher degrees of stratification of CNG resulted in more complete combustion.

Figure 29 shows the mass ratio of flow rates of CH4 in the exhaust emissions and mass flow rate of CNG injected into the cylinder. At a given constant gasoline equivalence ratio of φg = 0.20, CNG direct injection at 80 BTDC resulted in the least emission of CH4. Therefore, the combustion of CNG was more complete when it was stratified. CNG injection at 300 and 240 BTDC resulted in moderate levels of CH4 emissions, and highest values were obtained with CNG injection at 180 BTDC. This was due to the turbulence created and mixing conditions in the cylinder when the piston changed its direction at 180 BTDC.

Figure 24. Effect of CNG injection on the exhaust gas temperature.

Figure 25. Effect of degree of CNG stratification on NOx emission.

#### 3.2. Gasoline-CNG combustion behavior in constant volume combustion chamber

The effect of injection gap on the gasoline-compressed natural gas mixture (GCNG) mixture combustion is discussed below. The injection gap alteration gave direct impact on the mixture distribution inside the combustion chamber. There are five injection gaps tested, 0, 5, 10, 15, and 20 ms. These injection gaps are expected to be able to give direct control to the mixture distribution inside the chamber.

all combustion stages. While on the contrary, longer injection gap reduces the combustion efficiency, maximum pressure, THR and longer combustion delay for 90% GCNG. However, the trends of the combustion duration are similar, longer duration for longer injection gap. Figure 31 confirmed the variation of injection gap effect to the combustion process of the GCNG mixture. The turning point is shown between 70 and 80% GCNG mixture compositions. For all the mixture above 80% shows decreasing combustion efficiency with the increase in injection gaps which is contrary with the mixtures below 70% that show an increment of combustion efficiency with the increase of injection gaps. These differences

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may cause by the mixture distribution inside the chamber.

Figure 27. Effect of degree of CNG stratification on CO emissions.

Figure 26. Effect of degree of CNG stratification on NO2 formation.

The effect of injection gaps is shown in Figure 30. It shows two mixture compositions, 50 and 90% GCNG composition. The injection gap gives different effect between the two compositions. In 50% GCNG, longer injection gap gives higher combustion efficiency, maximum pressure, total heat released (THR) and shorter delay. Furthermore, it also shows longer duration for Reactivity Controlled Compression Ignition (RCCI) of Gasoline-CNG Mixtures http://dx.doi.org/10.5772/intechopen.72880 73

Figure 26. Effect of degree of CNG stratification on NO2 formation.

Figure 27. Effect of degree of CNG stratification on CO emissions.

3.2. Gasoline-CNG combustion behavior in constant volume combustion chamber

distribution inside the chamber.

Figure 24. Effect of CNG injection on the exhaust gas temperature.

72 Improvement Trends for Internal Combustion Engines

Figure 25. Effect of degree of CNG stratification on NOx emission.

The effect of injection gap on the gasoline-compressed natural gas mixture (GCNG) mixture combustion is discussed below. The injection gap alteration gave direct impact on the mixture distribution inside the combustion chamber. There are five injection gaps tested, 0, 5, 10, 15, and 20 ms. These injection gaps are expected to be able to give direct control to the mixture

The effect of injection gaps is shown in Figure 30. It shows two mixture compositions, 50 and 90% GCNG composition. The injection gap gives different effect between the two compositions. In 50% GCNG, longer injection gap gives higher combustion efficiency, maximum pressure, total heat released (THR) and shorter delay. Furthermore, it also shows longer duration for all combustion stages. While on the contrary, longer injection gap reduces the combustion efficiency, maximum pressure, THR and longer combustion delay for 90% GCNG. However, the trends of the combustion duration are similar, longer duration for longer injection gap. Figure 31 confirmed the variation of injection gap effect to the combustion process of the GCNG mixture. The turning point is shown between 70 and 80% GCNG mixture compositions. For all the mixture above 80% shows decreasing combustion efficiency with the increase in injection gaps which is contrary with the mixtures below 70% that show an increment of combustion efficiency with the increase of injection gaps. These differences may cause by the mixture distribution inside the chamber.

Figure 28. Effect of degree of CNG stratification on HC emissions.

Figure 30. Effect of injection gaps on the combustion characteristics of GCNG mixture for 50 and 90% composition at

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Figure 31. Effect of injection gap to the combustion efficiency for various mixture compositions at lambda 1.

lambda 1.

Figure 29. Effect of injection timing on the emission of CH4 with φg = 0.20.

The mixture distribution inside the chamber for GCNG mixture 30 and 90% with 0 and 20 ms injection gaps are depicted in Figure 32. In the figure, highly stratified mixture for 30% GCNG mixture with 0 ms injection gap. The stratification is marked by darker color on the bottom of the chamber that indicates high density fluid (gasoline). The image shows that most of the gasoline was collected at the bottom of the chamber because of the momentum of CNG injection that prevents the gasoline from reaching the top side of the chamber. 20 ms injection gap, on the other hand, shows better fuel mixing shown by fairly similar image intensity throughout the chamber.

The injection gaps for 30% GCNG mixture improve the mixing rate thus increase the combustion performance. Furthermore, the gasoline fuel is mainly accumulating at the bottom side

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Figure 30. Effect of injection gaps on the combustion characteristics of GCNG mixture for 50 and 90% composition at lambda 1.

The mixture distribution inside the chamber for GCNG mixture 30 and 90% with 0 and 20 ms injection gaps are depicted in Figure 32. In the figure, highly stratified mixture for 30% GCNG mixture with 0 ms injection gap. The stratification is marked by darker color on the bottom of the chamber that indicates high density fluid (gasoline). The image shows that most of the gasoline was collected at the bottom of the chamber because of the momentum of CNG injection that prevents the gasoline from reaching the top side of the chamber. 20 ms injection gap, on the other hand, shows better fuel mixing shown by fairly similar image intensity

The injection gaps for 30% GCNG mixture improve the mixing rate thus increase the combustion performance. Furthermore, the gasoline fuel is mainly accumulating at the bottom side

throughout the chamber.

Figure 28. Effect of degree of CNG stratification on HC emissions.

74 Improvement Trends for Internal Combustion Engines

Figure 29. Effect of injection timing on the emission of CH4 with φg = 0.20.

Figure 31. Effect of injection gap to the combustion efficiency for various mixture compositions at lambda 1.


Figure 32. Mixture distribution for 30 and 90% mixture composition at 0 and 20 ms injection gaps.

which also has average low temperature compared to the top one. It makes the vaporization rate of the gasoline took longer time which also elongates the combustion delay as shown in Figure 33.

shows that 0 ms injection gap have higher gasoline population compared to 20 ms injection gap thus the longer time required for vaporization process. This is the main reason for the lower combustion output as well as longer combustion delay for 0 ms compared to 20 ms

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Figure 34. Combustion sequence for GCNG at 60/40 mixture composition and lambda 1.

The combustion sequence for GCNG at 0 and 20 ms injection gaps is depicted in Figure 34. The flame speed of 20 ms injection gap is faster than 0 ms injection gap with 37.02 m/s at the first 0.5 ms and 15.9 at the first 1 ms after start of combustion (SOC), while 0 ms injection gap with 30.56 m/s and 16.9 m/s at 0.5 ms and 1 ms, respectively. Figure 34 also reveals the difference in the flame color for the two injection gaps. A 20 ms injection gap shows light blue color yet with

injection gap.

Figure 33. Combustion delay relative to SOI.

The injection gaps at 90% GCNG mixture, on the other hand, have similar liquid fuel distribution as in Figure 32 where both injection gaps show concentrated fuel distribution at the top of the chamber. In spite of the similarity, the 0 ms injection gap shows the higher intensity of the liquid fuel (darker region) on the top side of the chamber compared to 20 ms injection gap. It Reactivity Controlled Compression Ignition (RCCI) of Gasoline-CNG Mixtures http://dx.doi.org/10.5772/intechopen.72880 77

Figure 33. Combustion delay relative to SOI.

which also has average low temperature compared to the top one. It makes the vaporization rate of the gasoline took longer time which also elongates the combustion delay as shown in

Figure 32. Mixture distribution for 30 and 90% mixture composition at 0 and 20 ms injection gaps.

The injection gaps at 90% GCNG mixture, on the other hand, have similar liquid fuel distribution as in Figure 32 where both injection gaps show concentrated fuel distribution at the top of the chamber. In spite of the similarity, the 0 ms injection gap shows the higher intensity of the liquid fuel (darker region) on the top side of the chamber compared to 20 ms injection gap. It

Figure 33.

76 Improvement Trends for Internal Combustion Engines

Figure 34. Combustion sequence for GCNG at 60/40 mixture composition and lambda 1.

shows that 0 ms injection gap have higher gasoline population compared to 20 ms injection gap thus the longer time required for vaporization process. This is the main reason for the lower combustion output as well as longer combustion delay for 0 ms compared to 20 ms injection gap.

The combustion sequence for GCNG at 0 and 20 ms injection gaps is depicted in Figure 34. The flame speed of 20 ms injection gap is faster than 0 ms injection gap with 37.02 m/s at the first 0.5 ms and 15.9 at the first 1 ms after start of combustion (SOC), while 0 ms injection gap with 30.56 m/s and 16.9 m/s at 0.5 ms and 1 ms, respectively. Figure 34 also reveals the difference in the flame color for the two injection gaps. A 20 ms injection gap shows light blue color yet with

stages, while homogeneous mixture produces longer duration. This trend is applicable for

\*, Morgan Raymond Heikal1,3,

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both GCNG and DCNG mixtures.

, Abdul Rashid Abdul Aziz2

\*Address all correspondence to: rashid@utp.edu.my

3 Advanced Engineering Centre, University of Brighton, UK

ignition gasoline engine. JSAE Review. 1995;16(3):314

HCCI engine operating on a two-component fuel. SAE. 2010

SAE Technical Paper Series. vol. 2002-01-01; 2002

loads. Applied Energy. 2016;175:389-402

Journal of Engine Research. 2011;12(3):209-226

sandia.gov/ecn/tutorials/visualization.php

01-36; 1999. pp. 1999-01-3682

Ezrann Zharif Zainal Abidin<sup>1</sup> and Naveenchandran Panchatcharam<sup>4</sup>

1 Centre for Automotive Research and Electric Mobility, Universiti Teknologi Petronas,

[1] Aoyama T, Hattori Y, Mizuta J. An experimental study on premixed-charge compression

[2] Kokjohn SL, Hanson RM, Splitter D a, Reitz RD. Fuel reactivity controlled compression ignition (RCCI): A pathway to controlled high-efficiency clean combustion. International

[3] Musculus M. Combustion Regime Visualization. 2011. [Online]. Available: http://www.

[4] Stanglmaier RH, Roberts CE. Homogeneous charge compression ignition (HCCI): Benefits, compromises, and future engine applications. SAE Technical Paper Series. vol. 1999-

[5] Saitou K, Iijima A, Otagiri Y, Yoshida K, et al. A study of ignition characteristics of an

[6] Sjöberg M, Lars-Olof E, Eliassen T, Magnusson L, Ãngstrom HE. GDI HCCI: Effects of injection timing and air swirl on fuel stratification, combustion and emission formation.

[7] Agarwal AK, Singh AP, Maurya RK. Evolution, challenges and path forward for low temperature combustion engines. Progress in Energy and Combustion Science. 2017;61:1-56

[8] Wang Y, Yao M, Li T, Zhang W, Zheng Z. A parametric study for enabling reactivity controlled compression ignition (RCCI) operation in diesel engines at various engine

2 Institute of Transport and Infrastructure, Universiti Teknologi Petronas, Malaysia

Author details

Firmansyah<sup>1</sup>

Malaysia

References

4 Bharath University, India

Figure 35. Effect of injection gap for 60/40 gasoline/CNG composition at lambda 1.

lower intensity compared to 100% gasoline, while 0 ms injection gap shows yellow color. It can be assumed that the blue color is the product from the same reaction that generates hydroxyl peroxide and increases the combustion output of the mixture.

In 100% gasoline combustion, the blue flame occurs because of the homogeneous mixture that creates multipoint combustion behind the flame front that significantly increases the combustion output. A similar process occurs in the 20 ms injection gaps, mixture homogeneity is achieved with this mixture as the effect of CNG injection shown by longer combustion delay relative to the start of injection as depicted in Figure 35.

Injection gaps proved to have a direct influence on the fuel distribution inside the chamber, thus affecting the combustion characteristics of the mixture. The combustion process in the CVC is mostly affected by the characteristics of the fuel distribution inside the chamber at the time the combustion occurs. The injection gaps, in this case, highly affect the mixture distribution inside the chamber where longer gap promotes the mixing and create a mixture that is more homogeneous.
