Effect of hydrogen peroxide addition to methane fueled homogeneous charge compression ignition engines through numerical simulations

The effect of the direct injection of hydrogen peroxide into a port-injected methane fueled homogeneous charge compression ignition engine was investigated numerically. The injection of aqueous hydrogen peroxide was implemented as a means of combustion phasing control. A single-cylinder homogeneous charge compression ignition engine (2.43 L Caterpillar) was modeled using the Cantera 2.0 flame code toolkit, the GRI-Mech 3.0 chemical reaction mechanism, and a single-zone slider-crank engine model. Start of injection timing and the amount of injected hydrogen peroxide were manipulated to achieve desired combustion phasing under a wide range of intake temperatures. As the concentration of hydrogen peroxide is increased, the combustion phasing is advanced up to 22° for the conditions investigated in this study. This advancing effect is most pronounced at small concentrations (<10 g H2O2/kg CH4) and early injection timings (start of injection < 25° before top dead center). The model suggests hydrogen peroxide can be introduced as a means of combustion phasing control while maintaining the low emissions and peak in-cylinder pressures inherent in homogeneous charge compression ignition engines.


Introduction
Homogeneous Charge Compression Ignition (HCCI) has proven to be an attractive internal combustion technique in attaining low emissions and high fuel efficiency. 1 However, the dependence on auto-ignition through chemical kinetics creates difficulty in attaining a controlled ignition event, especially over a wide range of intake conditions. 2 Techniques for controlling the ignition event include managing the intake temperature through resistance heating of the intake air, 3,4 variable valve actuation, 5 and exhaust gas recirculation. 6][9][10][11] In this dual-fuel strategy, the difference in the combustion characteristics of each fuel is exploited to regulate the reactivity of the in-cylinder charge. 12Dual fuel strategies can either combine fuels as a premixed charge or through in-cylinder injection of a secondary fuel.This study proposes that hydrogen peroxide (H 2 O 2 ) may be a suitable additive to introduce through direct injection as a means of control.
Due to its role as a critical oxidizer in the initiation of thermal ignition, H 2 O 2 concentration is a main determinant of the rate of heat release. 13It has also been shown to increase gross indicated mean effective pressure (IMEP) and advance ignition timing. 14Therefore, the manipulation of the concentration of H 2 O 2 may allow for the control of the combustion event.It is also worth noting that H 2 O 2 is both inexpensive and readily available, thus making it a practical and economical choice as an additive.In application, use of the aqueous H 2 O 2 mixture for combustion timing would not be implemented for every cycle -only to overcome changes in operating conditions to maintain the engine at optimal combustion phasing.For a natural gas vehicle with a 10 GGE (Gasoline Gallon Equivalent) tank at an extreme case of secondary injection occurring at 10% of all cycles using a 1% H 2 O 2 solution, the total consumption of the aqueous mixture would be 0.68 gallons.
Previous studies have shown that pre-mixed fuels of H 2 O 2 in methane have drastically reduced the intake temperature required to achieve ignition at a given crank angle degree (CAD). 15The same findings were seen in engines running a mixture of H 2 0 2 and ethanol. 16However, the use of H 2 0 2 has not been investigated as a cycle-to-cycle controlling device; only as a combustion enhancer for pre-mixed fuels.
In order to take advantage of the beneficial characteristics of H 2 O 2 addition seen by other investigators, the authors employed H 2 O 2 as a means of control by studying the effects of directly injecting an aqueous H 2 O 2 solution into the combustion chamber of an HCCI engine through numerical simulations.
Additionally, as H 2 O 2 is typically transported in an aqueous mixture due to safety concerns, there will also be a significant amount of water introduced in the process of direct injecting the secondary fuel.8][19][20] The accompanying water may also have negative effects on the emissions of CO and unburned hydrocarbons. 17Furthermore, water injection may cause problems with operation or storage of the engine at sub-zero temperatures.

Objective and approach
A single-zone model was used to investigate the effect of H 2 O 2 addition through direct injection into a pre-mixed charge of methane in air.Parameters varied in the simulations include the start of injection (SOI), the intake temperature (T in ), and the amount of H 2 O 2 .In all trials, the injected liquid is an aqueous mixture of H 2 O 2 at a concentration of one percent by mass.This concentration was chosen for two reasons.First, this concentration is considered a stable mixture and a safe means of transporting H 2 O 2 in close proximity to a heat source.According to the United States Department of Labor's Occupational Safety and Health Administration, H 2 O 2 in concentrations above eight percent by mass is a potential fire or explosion hazard. 24Secondly, the total volume of aqueous H 2 O 2 introduced during the direct injection event is similar to amounts introduced in experimental studies which directly injected water 18 and light naptha. 25The amount of the aqueous H 2 0 2 mixture introduced in the simulations ranges from 0-0.3g/cycle.While this amount is significantly lower than in an engine where all the fuel is directly injected into the cylinder, it falls within an acceptable range for a direct injection system. 18panding on the analysis of the repercussions of the pure water accompanying the H 2 O 2 , Figure 1 displays pressure profiles with injections of varying concentrations of the aqueous H 2 O 2 mixture.The mass of H 2 O 2 was held constant at 0.5 mg for each of the four simulations in this figure, and the mass of the water was changed to achieve each concentration.An intake temperature of 440 K was used for these simulations.Combustion phasing is advanced as the H 2 O 2 concentration is increased.There are shortcomings of an unnecessarily low H 2 O 2 concentration, as the effects of the accompanying water oppose the effects of the H 2 O 2 .A diluted mixture requires a larger volume of injection thereby reducing the fuel efficiency.Conversely, enough water needs to be added to ensure the volume of the injection is sufficiently large to ensure proper functionality of the fuel injector.Additionally, low H 2 O 2 concentration may limit part degradation.Large quantities of the solution can alter the heat capacity ratio bringing concomitant thermal property changes in addition to the chemical effects.Figure 2 presents the heat capacity ratio as a function of the mass of injection.Gamma in Figure 2 was determined by adding H 2 O 2 and water to a methane and air gas mixture with an equivalence ratio of 0.3.The heat capacity ratio tends towards the heat capacity of steam as the mass of injection rises.This reduction in the heat capacity ratio is, in part, responsible for the reduction of peak in-cylinder temperatures with increased mass of injection.This will be discussed in more detail below.

Computational model
A single cylinder HCCI engine was modeled with MATLAB using the Cantera 2.0 flame code toolkit, 26 the GRI-Mech 3.0 chemical reaction mechanism, 27 and a single-zone slider-crank engine model. 28The GRI-Mech 3.0 chemical reaction mechanism incorporates 53 species and 325 reactions.As a result of the single-zone model disregarding the subtle mass, temperature, and pressure stratifications within the cylinder, it fails in providing reliable numerical values of emissions, temperatures, and peak in-cylinder pressures.However, a single-zone model does provide for a sufficient analysis of overall combustion trends.The single-zone model provides a reasonable approximation of HCCI combustion in that the entire charge ignites nearly simultaneously throughout the cylinder without a flame front. 16It has been shown that a single-zone model captures combustion phasing acceptably in comparison with multi-zone models. 29e engine modeled in these experiments is a six cylinder Caterpillar (CAT) 3406 modified for HCCI operation. 1A single cylinder is modeled in the simulations.Engine parameters are included in Table 1.The single-zone model used in these simulations was validated using experimental data from the CAT 3406 engine.
An ensemble average of 50 traces obtained during firing conditions using natural gas were used to tune the model. 1 The compression ratio of the single-zone model was reduced to 14 in order to reasonably match the simulated motoring trace and the experimental data.A connecting rod length of 262 mm was used in the simulation.Figure 3 shows a comparison between the experimental and numerical results.The results show that the simulation data are in relatively good agreement with the experimental results.The simulation occurs between bottom dead center (BDC) of the compression stroke and BDC of the power stroke.
The injection of the H 2 O 2 solution was modeled as a homogeneous addition to the combustion chamber.This solution was modeled as an aqueous mixture of one percent H 2 O 2 by mass.Methane was used as the primary fuel for this simulation because it does not readily achieve auto-ignition in HCCI and exhibits increased reactivity in the presence of H 2 O 2 . 30An overall equivalence ratio of 0.3 was maintained in these simulations.
The numerical simulation was performed at atmospheric intake pressure and at various intake temperatures to measure the relationships between H 2 O 2 concentration, start of injection (SOI) timing, and combustion timing.Combustion timing is measured by the crank angle at which fifty percent of the total heat has been released (CA50). 28

Results and discussion
It was found that the addition of small concentrations of H 2 O 2 provided a significant advance in combustion timing.In small concentrations, H 2 O 2 could induce combustion of methane under conditions that would otherwise result in a misfire.Small amounts of the aqueous H 2 0 2 mixture were introduced at a SOI of -5 CAD after top dead center (ATDC) to a cylinder with an intake temperature of 440 K and atmospheric intake pressure.Figure 4 shows that increased amounts of H 2 O 2 can advance the combustion event, which is evident by the steep increase in pressure.This shows a large variability in the combustion timings that can be achieved simply by manipulating the H 2 O 2 concentration.Additionally, it can be seen that the ability to advance combustion diminishes at higher concentrations of H 2 O 2 addition.While holding intake temperature and SOI constant, varying the concentration of H 2 O 2 influences combustion timing.However, the response of combustion timing to the addition of H 2 O 2 exponentially decays as CA50 approaches SOI (Figure 5).At an intake temperature 450 K and a SOI of -5 CAD ATDC, concentrations of 2, 10, and 20 g H 2 O 2 per kg of CH 4 achieve combustion at 33, 6, and 2 CA50 respectively.A similar effect is seen at other intake temperatures.Note that it is possible to achieve the same CA50 at a reduced intake temperature simply by increasing the concentration of H 2 O 2 .The intake conditions used in the simulations included in Figure 5 are such that the methane would not ignite in this HCCI engine; the addition of H 2 O 2 brings the engine out of a misfire regime.
∆CA50 is a useful diagnostic in determining the effectiveness of H 2 O 2 addition.Figure 7 shows ∆CA50 as a function of the concentration of H 2 O 2 .∆CA50 grows as the concentration of H 2 O 2 rises.Again, it is observed that H 2 O 2 addition has the greatest effect at lower concentrations and at lower intake temperatures.To expand the range in which the injection of H 2 O 2 provides a beneficial effect on combustion, injection timing was also utilized as an ignition control parameter.An advance in SOI while holding injected mass and intake temperature constant produced an advance in combustion timing.Figure 8 shows the effect of SOI changes at a constant concentration of 30 g H 2 O 2 per kg CH 4 and an intake temperature of 440 K.An early SOI can be detrimental to power output if it advances CA50 before top dead center (TDC).A late SOI can marginally increase the pressure during the expansion stroke.A well timed SOI can trigger the combustion event shortly after TDC and provide for a large power output.The relationship between SOI and CA50 has two important regimes, as shown in Figure 9.At very early SOI, a change in SOI has little effect on combustion timing.This minor effect is examined in more detailed below through an investigation of the evolution of the free radical concentration.However, as SOI increases towards a critical point, a change in SOI has an exponential effect on combustion timing.At lower temperatures this critical point demarcates the region where combustion cannot be achieved given the SOI and amount of injected solution.At higher temperatures this critical point demarcates the region where autoignition is reached before SOI (as indicated by the flat lines).The relationship between combustion phasing and SOI is seen across all intake temperatures.∆CA50 as a function of SOI at a constant injected mass of H 2 O 2 is shown in Figure 10.The largest effect on combustion timing for a given injected H 2 O 2 mass is seen at early SOI.The benefits of H 2 O 2 addition subside as SOI is delayed until it does not affect the combustion timing at very late SOI (> 15 CAD).It is again evident that H 2 O 2 addition has the greatest effect when operating at lower intake temperatures.The manipulation of SOI timing in conjunction with the manipulation of H 2 O 2 concentration provides two tools which can be utilized to achieve desired combustion timing under a wide range of intake conditions.A desired CA50 can be achieved with a number of different combinations of SOI and H 2 O 2 concentration.Figure 11 shows a contour plot of the CA50 achieved given the SOI and H 2 O 2 concentration.This simulation was conducted at atmospheric intake pressure and an intake temperature of 460 K.At these conditions, CA50 occurs at 12.1 CAD when there is no H 2 O 2 injection.The slope of the contour line with respect to SOI approaches zero as SOI decreases and the slope of the contour line with respect to H 2 O 2 concentration approaches zero as H 2 O 2 concentration increases.However, manipulation of these parameters simultaneously provides a large range of CA50 that can be achieved.A detailed look at the time series evolution of key species inside the combustion chamber sheds additional light into the effect of H 2 O 2 addition on the ignition process.Figure 13 shows a simulation with constant H 2 O 2 addition of 100 mg, an intake temperature of 440 K, and a SOI -5 CAD.The SOI event is evident by a spike in H 2 O 2 concentration.The H 2 O 2 quickly dissociates into hydrogen (H), hydroxide (OH), and hydroperoxyl (HO 2 ) radicals.The presence of these radicals increases reactions with the methane molecules, leading towards the ignition event.The manipulation of the mass of the H 2 O 2 addition can directly affect the concentration of free radicals.Figure 14 shows the time series evolution of the mass fraction of OH under varied injection amounts.These simulations were performed with a SOI of -5 CAD an intake temperature of 440 K.It can be seen that if enough radicals can be produced then combustion can be achieved.The radical concentrations of simulations that achieved combustion were several orders of magnitude larger the than radical concentrations of the simulations that misfired.This difference is not attributable to the difference in injected H 2 O 2. Rather, if sufficient H 2 O 2 is added then the radical concentration rapidly grows as the methane decomposes.Furthermore, radical concentrations of simulations that achieved combustion reached similar peak levels of radicals.Additionally, the SOI of the H 2 O 2 addition is a critical determinant of the time series evolution of free radicals.Figure 15 shows the time series evolution of the mass fraction of OH under varied SOI.These simulations were performed with a 100 mg injection and an intake temperature of 440 K. Advancing SOI allows the rapid growth of radicals to occur sooner.This advances CA50 in the region around TDC.However, for early SOI, the temperature is not yet high enough to trigger the combustion event soon after the injection.For these early SOI simulations, the radical concentration remains elevated until the temperature is high enough to cause rapid decomposition of methane.This results in the loss of effectiveness of early SOI.The use of H 2 O 2 as a secondary fuel in HCCI may provide control over combustion timing while retaining the benefits that make HCCI an attractive technique.In order to test the effects of H 2 O 2 on pressure, temperature, and exhaust emissions, combustion timing was held constant so that the effects of H 2 O 2 are isolated from the effects of combustion timing.As is the case in all single-zone engine simulations that disregard the subtle mass, temperature, and pressure stratifications within the cylinder, the values of emissions, temperatures, and peak in-cylinder pressures are most useful when viewed qualitatively with respect to the other simulations.While quantitative evaluations can be highly uncertain, the trends presented in the following figures are important in understanding the impact of H 2 O 2 injection on the in-cylinder combustion process.First, the simulations suggest that H 2 O 2 injection does not have significant repercussions on peak pressures within the cylinder; an important consideration since high peak pressures can damage the engine. 31     The reduction in peak temperature has a beneficial influence on emissions since they are heavily dependent on temperature. 32  Furthermore, because the increased concentration of radicals promotes the decomposition of organic compounds, increasing H 2 O 2 concentration increases combustion completeness.As a result, exhaust CO lessens as the H 2 O 2 concentration is increased.Figure 20 shows the decreasing trend in exhaust CO mole fraction as the H 2 O 2 concentration is increased.SOI was adjusted to achieve a CA50 of 3 ± 0.3 CAD for all trials.Although a single-zone model may be insufficient to gather the effects of unburned charge trapped in piston crevices 33 , these emissions trends are enough to encourage further investigation.Figure 22 shows the effect of the amount of H 2 O 2 addition on the HRR at an intake temperature of 460 K and a SOI of -5 CAD.As the amount of added H 2 O 2 increases, the timing of the peak HRR advances with combustion timing.Similarly, Figure 23 shows the effect of SOI on the HRR at an intake temperature of 460 K and a 100 mg H 2 O 2 solution injection.As the SOI is advanced, the peak HRR advances with combustion timing.Maximum HRR is achieved when combustion occurs shortly after TDC.

Conclusions
The effects of the direct injection of aqueous H 2 O 2 into a methane fueled HCCI engines were investigated numerically.This study suggests that a directly injected aqueous mixture of H 2 O 2 can provide the ability to control combustion phasing in HCCI engines while preserving low emissions and high efficiencies.The introduction of small quantities of H 2 O 2 can effectively advance the ignition of methane.The application of direct injection of H 2 O 2 has the potential to negate some of the difficulties associated with controlling the combustion event and expand the range of combustion regimes at which HCCI operates.The manipulation of H 2 O 2 concentration and SOI provides two tools which can be utilized to achieve desired combustion timing under a wide range of intake conditions.This can be achieved while maintaining low emissions and peak in-cylinder pressures.
While the results of this experiment are promising, the expansion of the computational model to multiple zones in order to capture the non-homogenous nature of the H 2 O 2 injection will yield further insight into the behavior of the dual fuel combustion control strategy.Additionally, the effect of higher intake pressures on the viability of H 2 O 2 addition needs to be addressed since many HCCI engines are now incorporating boosted operating conditions to increase the power density of the engine.Further investigation through experimentation or an expansion of the single-zone model into a multi-zone model is necessary to validate the strategy.

Figure 1 .
Figure 1.The effects on the temperature profile created by equivalent injections of pure water and aqueous H 2 O 2 have on CA50 when SOI is -5 CAD and the intake temperature is 460 K.

Figure 2 .
Figure 2. Heat capacity ratio as a function of the mass of injection.The concentration of the aqueous H 2 O 2 mixture is 1% by mass.

Figure 3 .
Figure 3.Comparison of the in-cylinder pressure for experimental and numerical data.

Figure 4 .
Figure 4. Effect of the quantity of injected solution on the pressure trace.Performed at an intake temperature of 440 K and a SOI of -5 CAD.

Figure 5 .
Figure 5.The relationship between the injected amount of H 2 O 2 and CA50 for different temperatures when SOI is -5 CAD.The change in CA50 shown in Figure5is due to the H 2 O 2 in the mixture.Although the addition of water has been shown to delay combustion in HCCI, aqueous hydrogen peroxide additions can advance combustion phasing despite the low concentration of H 2 O 2 .Figure6shows a comparison between the CA50 attained when equal injections of pure water and aqueous hydrogen peroxide are directly injected at -5 SOI.Combustion is delayed as more water is introduced.Conversely, combustion is advanced as more aqueous H 2 O 2 is added.Although the water accompanying the H 2 O 2 may produce a cooling effect that decreases the combustion rate, the chemical effect of the H 2 O 2 is significant enough to advance combustion phasing.Therefore, CA50 advances significantly when H 2 O 2 is present in the secondary injection when compared to water alone.

Figure 6 .
Figure 6.The effects on CA50 of injections of pure water and aqueous H 2 O 2 have on CA50 when SOI is -5 CAD and the intake temperature is 460 K.The concentration of the aqueous H 2 O 2 mixture is 1% by mass.

Figure 7 .
Figure 7.The relationship between the injected amount of H 2 O 2 and ∆CA50 for different temperatures when SOI is -5 CAD.

Figure 8 .
Figure 8.Effect of the start of injection on the pressure trace.Performed at an intake temperature of 440 K and a constant concentration of 30 g H 2 O 2 per kg CH 4 .

Figure 9 .
Figure 9.The relationship between the SOI of H 2 O 2 and CA50 at different intake temperatures and 100 mg of injected solution.

Figure 10 .
Figure 10.The relationship between the SOI of H 2 O 2 and ∆CA50 at different intake temperatures and 100 mg of injected solution.

Figure 11 .
Figure 11.The combined effects of H 2 O 2 concentration and SOI on CA50 at an intake temperature of 460 K.The same data used to generate the CA50 contour plot above is used to plot the ∆CA50 contour plot in Figure 12.In this figure we can see the combined effect of SOI and H 2 O 2 concentration on ∆CA50.The slope of the contour line with respect to SOI approaches zero as SOI decreases.The slope of the contour line with respect to H 2 O 2 concentration approaches zero as H 2 O 2 concentration increases.Once SOI is increased past the crank angle where combustion occurs in the absence of H 2 O 2 , ∆CA50 remains zero.∆CA50 is advanced as SOI is advanced and H 2 O 2 concentration is increased.

Figure 12 .
Figure 12.The combined effects of H 2 O 2 concentration and SOI on the change in CA50 with respect to the CA50 achieved without H 2 O 2 injection at an intake temperature of 460 K.

Figure 13 .
Figure 13.The evolution of four chemical species (H 2 O 2 , OH, H, HO 2 ) over time.Simulation was performed with a SOI of -5 CAD, an intake temperature of 440 K, and an injected mass of 100 mg.The vertical red line demarcates CA50.

Figure 14 .
Figure 14.The effect of the amount of H 2 O 2 on the evolution of hydroxide over time.Simulation was performed with and SOI of -5 CAD and an intake temperature of 440 K.The vertical red line demarcates CA50.

Figure 15 .
Figure 15.This Figure shows the effect of the SOI of H 2 O 2 on the evolution of hydroxide over time.The vertical red line demarcates CA50.

Figure 16
exhibits the effect of H 2 O 2 concentration on peak pressure.SOI was adjusted to achieve a CA50 of 3 ± 0.3 CAD for all simulations.As the concentration of H 2 O 2 increases, the peak in-cylinder pressure slightly decreases.Notwithstanding the over-prediction of the quantitative peak pressure results produced by the single-zone model, the qualitative trend produced by the model bolsters the notion that the H 2 O 2 direct injection strategy should be explored more rigorously.

Figure 16 .
Figure 16.The relationship between the concentration of H 2 O 2 and peak in-cylinder pressures while CA50 is held constant at 3 ± 0.3 CAD.The reduction of peak in-cylinder pressure presented above is likely a ramification of decreasing in-cylinder temperatures.Figure17exhibits the effect of H 2 O 2 concentration on peak temperature.SOI was adjusted to achieve a CA50 of 3 ± 0.3 CAD for all simulations.As more aqueous H 2 O 2 is introduced, the mean specific heat increases and the gas mixture becomes more resistant to temperature change.Therefore, the peak temperature declines as the concentration of H 2 O 2 is raised.

Figure 17 .
Figure 17.The relationship between the concentration of H 2 O 2 and peak in-cylinder temperatures while CA50 is held constant at 3 ± 0.3 CAD.

Figure 18
Figure 18 presents these trends from another perspective.In this figure, the temperature profile is seen over CAD for five different cases.First, the figure includes the temperature profile of a cycle with no injection with an intake temperature of 460 K.The temperature profile of a small injection (10 g H2O2 / kg CH4) of aqueous H2O2 was

Figure 18 .
Figure 18.The effects on the temperature profile created by equivalent injections of pure water and aqueous H 2 O 2have on CA50 when SOI is -5 CAD and the intake temperature is 460 K.

Figure 19
exhibits the effect of H 2 O 2 concentration on the NO x emissions.In this simulation, SOI was adjusted to achieve a CA50 of 3 ± 0.3 CAD for all trials.The simulations showed that the addition of H 2 O 2 has a positive effect on the emissions of NO x .Moreover, the addition of H 2 O 2 can allow the engine to run at lower temperatures and maintain the same CA50, thereby indirectly decreasing the emissions of NO x .

Figure 19 .
Figure 19.The relationship between the concentration of H 2 O 2 and the emissions of NO x while CA50 is held constant at 3 ± 0.3 CAD.

Figure 20 .
Figure 20.The relationship between the concentration of H 2 O 2 and the emissions of CO while CA50 is held constant at 3 ± 0.3 CAD.Pressure analysis was performed to calculate the indicated mean effective pressure (IMEP), the heat release rate (HRR), and the cumulative heat release (CHR).Figure 21 depicts the effect of the H 2 O 2 addition on the IMEP while holding CA50 constant.As the concentration of H 2 O 2 increases, IMEP tends to decrease due to the additional water present in the combustion chamber.As shown in Figures 16 and 17, the additional water decreases the peak in-cylinder pressure and temperature and thus the trend of decreasing IMEP at higher H 2 O 2 concentrations.

Figure 21 .
Figure 21.The effect of the concentration of H 2 O 2 on IMEP.CA50 is held constant at 3 ± 0.3 CAD.

Figure 22 .
Figure 22.The effect of the amount of H 2 O 2 on the heat release rate.SOI is held constant at -5 CAD and intake temperature is 460 K.

Figure 23 .
Figure 23.The effect of the SOI of 100 mg of solution on the heat release rate at an intake temperature is 460 K.

Figure 24
Figure24shows the effect of the amount of H 2 O 2 addition on the CHR at an intake temperature of 460 K and a SOI of -5 CAD.As the amount of added H 2 O 2 increases, the CHR decreases due to lower in-cylinder peak temperatures.Combustion did not occur when the SOI was 10 and 20 CAD.Figure25shows the effect of SOI on the CHR at an

34 Figure 24 .
Figure24shows the effect of the amount of H 2 O 2 addition on the CHR at an intake temperature of 460 K and a SOI of -5 CAD.As the amount of added H 2 O 2 increases, the CHR decreases due to lower in-cylinder peak temperatures.Combustion did not occur when the SOI was 10 and 20 CAD.Figure25shows the effect of SOI on the CHR at an

Figure 25 .
Figure 25.The effect of the SOI of 100 mg of solution on the cumulative heat release at an intake temperature is 460 K.