Investigation of the effects of hydrogen on cylinder pressure in a split-injection diesel engine at heavy EGR

The distinctive properties of hydrogen have initiated considerable applied research related to the internal combustion engine. Recently, it has been reported that NO_x emissions were reduced by using hydrogen in a diesel engine at low temperature and heavy EGR conditions. As the continuing study, cylinder pressure was also investigated to determine the combustion characteristics and their relationship to NO_x emissions. The test engine was operated at constant speed and fixed diesel fuel injection rate (1500 rpm, 2.5 kg/h). Diesel fuel was injected in a split pattern into a 2-L diesel engine. The cylinder pressure was measured for different hydrogen flow rates and EGR ratios. The intake manifold temperature was controlled to be the same to avoid the gas intake temperature variations under the widely differing levels (2%-31%) of EGR. The measured cylinder pressure was analyzed for characteristic combustion values, such as mass burn fraction and combustion duration.The rising crank angle of the heat release rate was unaffected by the presence of hydrogen. However, supplying hydrogen extended the main combustion duration. This longer main combustion duration was particularly noticeable at the heavy EGR condition. It correlated well with the reduced NO_x emissions.     

An experimental investigation on engine performance and emissions of a supercharged H2-diesel dual-fuel engine

This study investigated the engine performance and emissions of a supercharged engine fueled by hydrogen and ignited by a pilot amount of diesel fuel in dual-fuel mode. The engine was tested for use as a cogeneration engine, so power output while maintaining a reasonable thermal efficiency was important. Experiments were carried out at a constant pilot injection pressure and pilot quantity for different fuel-air equivalence ratios and at various injection timings without and with charge dilution. The experimental strategy was to optimize the injection timing to maximize engine power at different fuel-air equivalence ratios without knocking and within the limit of the maximum cylinder pressure. The engine was tested first with hydrogen-operation condition up to the maximum possible fuel-air equivalence ratio of 0.3. A maximum IMEP of 908 kPa and a thermal efficiency of about 42% were obtained. Equivalence ratio could not be further increased due to knocking of the engine. The emission of CO was only about 5 ppm, and that of HC was about 15 ppm. However, the NOx emissions were high, 100–200 ppm or more. The charge dilution by N₂ was then performed to obtain lower NOx emissions. The 100% reduction of NOx was achieved. Due to the dilution by N₂ gas, higher amount of energy could be supplied from hydrogen without knocking, and about 13% higher IMEP was produced than without charge dilution.     

An analytic study of applying Miller cycle to reduce NOx emission from petrol engine

An analytic investigation of applying Miller cycle to reduce nitrogen oxides (NO_x) emissions from a petrol engine is carried out. The Miller cycle used in the investigation is a late intake valve closing version. A detailed thermodynamic analysis of the cycle is presented. A comparison of the characters of Miller cycle with Otto cycle is presented. From the results of thermodynamic analyses, it can be seen that the application of Miller cycle is able to reduce the compression pressure and temperature in the cylinder at the end of compression stroke. Therefore, it lowers down the combustion temperature and NO_x formation in engine cylinder. These results in a lower exhaust temperature and less NO_x emissions compared with that of Otto cycle. The analytic results also show that Miller cycle ratio is a main factor to influence the combustion temperature, and then the NO_x emissions and the exhaust temperature. The results from the analytic study are used to analyse and to compare with the previous experimental results. An empirical formula from the previous experimental results that showed the relation of NO_x emissions with the exhaust temperature at different engine speed is presented. The results from the study showed that the application of Miller cycle may reduce NO_x emissions from petrol engine.     

Performance and emission comparison of a supercharged dual-fuel engine fueled by producer gases with varying hydrogen content

This study investigated the effect of hydrogen content in producer gas on the performance and exhaust emissions of a supercharged producer gas–diesel dual-fuel engine. Two types of producer gases were used in this study, one with low hydrogen content (H₂ = 13.7%) and the other with high hydrogen content (H₂ = 20%). The engine was tested for use as a co-generation engine, so power output while maintaining a reasonable thermal efficiency was important. Experiments were carried out at a constant injection pressure and injection quantity for different fuel–air equivalence ratios and at various injection timings. The experimental strategy was to optimize the injection timing to maximize engine power at different fuel–air equivalence ratios without knocking and within the limit of the maximum cylinder pressure. Two-stage combustion was obtained; this is an indicator of maximum power output conditions and a precursor of knocking combustion. Better combustion, engine performance, and exhaust emissions (except NO_x) were obtained with the high H₂-content producer gas than with the low H₂-content producer gas, especially under leaner conditions. Moreover, a broader window of fuel–air equivalence ratio was found with highest thermal efficiencies for the high H₂-content producer gas.     

A simulation of the combustion of hydrogen in HCCI engines using a 3D model with detailed chemical kinetics

The influence of changes in the swirl velocity of the intake mixture on the combustion processes within a homogeneous charge compression ignition (HCCI) engine fueled with hydrogen were investigated analytically. A turbulent transient 3D predictive computational model which was developed and applied to the HCCI engine combustion system, incorporated detailed chemical kinetics for the oxidation of hydrogen. The effects of changes in the initial intake swirl, temperature and pressure, engine speed and compression and equivalence ratios on the combustion characteristics of a hydrogen fuelled HCCI engine were also examined. It is shown that an increase in the initial flow swirl ratio or speed lengthens the delay period for autoignition and extends the combustion period while reducing NO_x emissions. There are optimum values of the initial swirl ratio and engine speed for a certain mixture intake temperature, pressure, compression and equivalence ratios operational conditions that can achieve high thermal efficiencies and low NO_x emissions while reducing the tendency to knock     

Impact of H2 addition on flame stability and pollutant emissions for an atmospheric kerosene/air swirled flame of laboratory scaled gas turbine

The purposes of this study are to compare the stability domains and the pollutant emissions when combustion occurs with and without addition of H₂ to a kerosene (Jet A1)/air premixed prevaporised mixture injected in a lean gas turbine combustor. Chemiluminescence of CH*, pollutant emissions (NO_x and CO) and pressure fluctuations data are simultaneously collected in order to determine the effects of H₂ addition on the stability of the combustion and on the flame structure for an inlet temperature of 473 K, atmospheric pressure and for a large range of equivalence ratio (from 0.3 to 1). Addition of hydrogen enables keeping stable combustion conditions when, for the same kerosene mass flow, the flame becomes lifted and very unstable. As for pollutant emissions, results show that the equivalence ratio is the key parameter to control NO_x emission even in the situation where the combustion power is increased due to H₂ addition. As H₂ addition strongly increases the flammability limits and the combustion stability domain, stable combustion can occur at leaner equivalence ratio and then decreases CO and NO_x emissions. This is an important fact since no substitution effect takes place in the reduction of NO_x and CO emissions. Study at constant combustion power and equivalence ratio by adjusting hydrogen and kerosene mass flow shows again a decrease in the pollutant emissions. Hydrogen injection in power generation systems using combustion seems to be a promising way in combustion research since due to the combined effects of enlarging combustion stability domain and reducing NO_x emissions by substituting kerosene to the benefit of H₂.     

Generating efficiency and emissions of a spark-ignition gas engine generator fuelled with biogas–hydrogen blends

We investigated the generating efficiency and pollutant emissions of a four-stroke spark-ignition gas engine generator operating on biogas–hydrogen blends of varying excess air ratios and hydrogen concentrations. Experiments were carried out at a constant engine speed of 1200 rpm and a constant electric power output of 10 kW. The experimental results showed that the peak values of generating efficiency, maximum cylinder pressure, and NO_x emissions were elevated at an excess air ratio of around 1.2 as the hydrogen concentration was increased. CO₂ emissions decreased as the excess air ratio and hydrogen concentration increased, due to lean-burn conditions and hydrogen combustion. An efficiency per NO_x emissions ratio (EPN) was defined to consider the relationship between the generating efficiency and NO_x emissions. A maximum EPN value of 0.7502 was obtained with a hydrogen concentration of 15%, for an excess air ratio of 2.0. At this EPN value, the NO_x and CO₂ emissions were 39 ppm and 1678.32 g/kWh, respectively, and the generating efficiency was 29.26%. These results demonstrated that the addition of hydrogen to biogas enabled the effective generation of electricity using a gas engine generator through lean-burn combustion.     

An experimental investigation on performance and emissions study with port injection using diesel as an ignition source for different EGR flow rates

Exhaust gas recirculation, EGR, is one of the most effective means of reducing NO_x emissions from IC engines and is widely used in order to meet the emission standards. In the present work, experimental investigation has been carried out to study the NO_x reduction characteristics by exhaust gas recirculation in a dual fueled engine using hydrogen and diesel. A single cylinder diesel engine was converted to operate on hydrogen-diesel dual fuel mode. Hydrogen was injected in intake port and diesel was injected directly inside the cylinder. The injection timing and injection duration of hydrogen were optimized initially based on the performance and emissions. It was observed that start of injection at 5° before gas exchange top dead center (BGTDC) and injection duration of 30° crank angle gives the best results. The flow rate of hydrogen was optimized as 7.5 lpm for the best start of injection and injection duration of hydrogen. Cold exhaust gas recirculation technique was adopted for the optimized injection parameter of hydrogen and flow rate. Maximum quantity of exhaust gases recycled during the test was 25% beyond this the combustion was not stable resulting in increase in smoke.     

Engine performance and emissions of a diesel engine operating on diesel-RME (rapeseed methyl ester) blends with EGR (exhaust gas recirculation)

The effects of biodiesel (rapeseed methyl ester, RME) and different diesel/RME blends on the diesel engine NO_x emissions, smoke, fuel consumption, engine efficiency, cylinder pressure and net heat release rate are analysed and presented. The combustion of RME as pure fuel or blended with diesel in an unmodified engine results in advanced combustion, reduced ignition delay and increased heat release rate in the initial uncontrolled premixed combustion phase. The increased in-cylinder pressure and temperature lead to increased NO_x emissions while the more advanced combustion assists in the reduction of smoke compared to pure diesel combustion. The lower calorific value of RME results in increased fuel consumption but the engine thermal efficiency is not affected significantly. When similar percentages (% by volume) of exhaust gas recirculation (EGR) are used in the cases of diesel and RME, NO_x emissions are reduced to similar values, but the smoke emissions are significantly lower in the case of RME. The retardation of the injection timing in the case of pure RME and 50/50 (by volume) blend with diesel results in further reduction of NO_x at a cost of small increases of smoke and fuel consumption.     

Direct injection of hydrogen main fuel and diesel pilot fuel in a retrofitted single-cylinder compression ignition engine

Up to 90% hydrogen energy fraction was achieved in a hydrogen diesel dual-fuel direct injection (H2DDI) light-duty single-cylinder compression ignition engine. An automotive-size inline single-cylinder diesel engine was modified to install an additional hydrogen direct injector. The engine was operated at a constant speed of 2000 revolutions per minute and fixed combustion phasing of ?10 crank angle degrees before top dead centre (°CA bTDC) while evaluating the power output, efficiency, combustion and engine-out emissions. A parametric study was conducted at an intermediate load with 20–90% hydrogen energy fraction and 180-0 °CA bTDC injection timing. High indicated mean effective pressure (IMEP) of up to 943 kPa and 57.2% indicated efficiency was achieved at 90% hydrogen energy fraction, at the expense of NO_x emissions. The hydrogen injection timing directly controls the mixture condition and combustion mode. Early hydrogen injection timings exhibited premixed combustion behaviour while late injection timings produced mixing-controlled combustion, with an intermediate point reached at 40 °CA bTDC hydrogen injection timing. At 90% hydrogen energy fraction, the earlier injection timing leads to higher IMEP/efficiency but the NO_x increase is inevitable due to enhanced premixed combustion. To keep the NO_x increase minimal and achieve the same combustion phasing of a diesel baseline, the 40 °CA bTDC hydrogen injection timing shows the best performance at which 85.9% CO₂ reduction and 13.3% IMEP/efficiency increase are achieved.     

An investigation of optimum control of ignition timing and injection system in an in-cylinder injection type hydrogen fueled engine

It is already known that the emission characteristic of hydrogen fueled engines are extremely good, when running the engine under lean burn conditions, with excess air ratios λ>2 which lower the NO_x emissions (Int. J. Hydrogen Energy 4 (1997) 423). However, there are abnormal combustion in the engine, which is one of the factors that has prevented the practical use of the engine. It is also a common conclusion that abnormal combustion can be suppressed in the in-cylinder injection type engine (International Fuels and Lubricants Meeting and Exposition, Philadelphia, PA, 6–9 October, SAE Technical Paper Series No. 8615769, 1986; Int. J. Hydrogen Energy 2 (1977) 329). But, such advantages as suppression of abnormal combustion, engine power-up and reduction of NO_x emission are gained depending on proper injection system and reasonable injection timing, ignition timing and law of hydrogen injection. In this study, Hydrogen is injected into the cylinder in the late compression stroke and is ignited by electric spark in a test engine. The research on the performance of hydrogen fueled engine is carried out under the condition of different ignition timing and injection timing. Further, a control system consisting of a fuzzy-neural network controller combining with ignition adaptive controller is applied to the engine in order to optimally control ignition timing, injection timing and cycle amount of hydrogen injection. Thus, the performances in the hydrogen engine attain optimization in every operating state of the engine.     

NOx reduction and NO2 emission characteristics in rich-lean combustion of hydrogen

Hydrogen is a clean alternative to conventional hydrocarbon fuels, but it is very important to reduce the nitrogen oxides (NO_x) emissions generated by hydrogen combustion. The rich-lean combustion or staged combustion is known to reduce NO_x emissions from continuous combustion burners such as gas turbines and boilers, and NO_x reduction effects have been demonstrated for hydrocarbon fuels. The authors applied rich-lean combustion to a hydrogen gas turbine and showed its NO_x reduction effect in previous research. The present study focused on experimental measurements of NO and NO₂ emissions from a coaxial rich-lean burner fueled with hydrogen. The results were compared with diffusion combustion and methane rich-lean combustion. Significant reductions in NO and NO₂ were achieved with rich-lean combustion. The NO and NO₂ reduction effects by rich-lean combustion relative to conventional diffusion combustion were higher with hydrogen than with methane.     

Experimental study of the performances of a modified diesel engine operating in homogeneous charge compression ignition (HCCI) combustion mode versus the original diesel combustion mode

Homogeneous charge compression ignition (HCCI) combustion mode provides very low NO_x and soot emissions; however, it has some challenges associated with hydrocarbon (HC) emissions, fuel consumption, difficult control of start of ignition and bad behaviour to high loads. Cooled exhaust gas recirculation (EGR) is a common way to control in-cylinder NO_x production in diesel and HCCI combustion mode. However EGR has different effects on combustion and emissions, which are difficult to distinguish. This work is intended to characterize an engine that has been modified from the base diesel engine (FL1 906 DEUTZ-DITER) to work in HCCI combustion mode. It shows the experimental results for the modified diesel engine in HCCI combustion mode fueled with commercial diesel fuel compared to the diesel engine mode. An experimental installation, in conjunction with systematic tests to determine the optimum crank angle of fuel injection, has been used to measure the evolution of the cylinder pressure and to get an estimate of the heat release rate from a single-zone numerical model. From these the angle of start of combustion has been obtained. The performances and emissions of HC, CO and the huge reduction of NO_x and smoke emissions of the engine are presented. These results have allowed a deeper analysis of the effects of external EGR on the HCCI operation mode, on some engine design parameters and also on NO_x emission reduction.     

Application of the Miller cycle to reduce NOx emissions from petrol engines

A conceptual analysis of the mechanism of the Miller cycle for reducing NO_x emissions is presented. Two versions of selected Miller cycle (1 and 2) were designed and realized on a Rover “K” series 16-valve twin-camshaft petrol engine. The test results showed that the application of the Miller cycle could reduce the NO_x emissions from the petrol engine. For Miller cycle 1, the least reduction rate of NO_x emission was 8% with an engine-power-loss of 1% at the engine’s full-load, compared with that of standard Otto cycle. For Miller cycle 2, the least reduction rate of NO_x emission was 46% with an engine-power-loss of 13% at the engine’s full-load, compared with that of standard Otto cycle.     

Comparison of the effects of EGR and lean burn on an SI engine fueled by hydrogen-enriched low calorific gas

A naturally aspirated spark ignition (SI) engine fueled by hydrogen-blended low calorific gas (LCG) was tested in both exhaust gas recirculation (EGR) and lean burn modes. The “dilution ratio” was introduced to compare their effects on engine performance and emissions under identical levels of dilution. LCG composed of 40% natural gas and 60% nitrogen was used as a main fuel, and hydrogen was blended with the LCG in volumes ranging from 0 to 20%. The engine test results demonstrated that EGR operations at stoichiometry showed a narrower dilution range, inferior combustion characteristics, lower brake thermal efficiency, faster nitrogen oxides (NO_x) suppression, and higher total hydrocarbon (THC) emissions for all hydrogen blending rates compared to lean burn. These trends were mainly due to the increased oxygen deficiency as a result of using EGR in LCG/air mixtures. Hydrogen enrichment of the LCG improved combustion stability and reduced THC emissions while increasing NO_x. In terms of efficiency, hydrogen addition induced a competition between combustion enhancement and increases in the cooling loss, so that the peak thermal efficiency occurred at 10% H₂ with excess air ratio of 1.5. The engine test results also indicated that a close-to-linear NO_x-efficiency relationship occurred for all hydrogen blending rates in both operations as long as stable combustion was achieved. NO_x versus combustion duration analysis showed that adding H₂ reduced combustion duration while maintaining the same level of NO_x. The methane fraction contained in the THC emissions decreased slightly with an increase in hydrogen enrichment at low EGR or excess air dilution ratios, but this tendency was diminished at higher dilution ratios because of the combined dilution effects from the inert gas in the LCG and the diluents (EGR or excess air).     

Emission and performance estimation in hydrogen injection strategies on diesel engines

Recently, the increasing demand for energy requires the use of alternative fuels, especially in fossil fueled power systems. As a promising alternative fuel for next-generation diesel engines that utilize fossil fuel, hydrogen fuel is one step ahead due to its positive properties. In this study, the effects of hydrogen on the performance of a diesel engine have been numerically investigated with respect to different injection ratios and timings. The numerical results of the study for 25% load conditions on a single-cylinder, four-stroke diesel engine have been validated against experimental data taken from literature and good agreement has been observed for pressure results. Emission parameters such as NO_x, CO and performance parameters such as cylinder temperature, pressure, power, thermal efficiency and IMEP are presented comparatively.The results of numerical analyses show that the maximum pressure, temperature and heat release rate are observed with injection ratio of H15 and early injection timing (20° CA BTDC). Besides that, engine power, thermal efficiency and IMEP are greatly improved with increasing injection ratio and early injection timing. Although combustion chamber performance parameters improve with rising the hydrogen injection ratio, higher NO_x emissions have also been detected as a negative side effect. Furthermore, while early injection timing increases diesel engine performance, it also causes an increase in NO_x emissions. Therefore, precise determination of injection timing together with the optimum amount of hydrogen has revealed that it brings crucial improvement in engine performance and emissions.     

The effects of hydrogen addition on engine power and emission in DME premixed charge compression ignition engine

Premixed-charge compression-ignition (PCCI) combustion of dimethyl-ether (DME) with double injection strategy was investigated in a single-cylinder compression-ignition engine. DME main-injection was replaced by hydrogen to reduce carbon dioxide emissions. To study the effect of hydrogen, the injected amount of hydrogen was increased. Engine performance and emission of DME PCCI combustion were compared to those of hydrogen–DME PCCI combustion. In the DME PCCI engine operation, DME was injected directly into the cylinder at −120 crank angle degrees (°CA) after top dead center (aTDC) to simulate homogeneous charge at first, and then DME was injected secondly with varied second injection timing. In this case, DME injection timing in the second stage affected the engine performance and emissions. Delayed combustion phase showed a higher indicated mean effective pressure (IMEP), while it increased NO_x emission when DME second injection is retarded. In the hydrogen–DME PCCI, hydrogen was injected at intake port with fixed injection timing. DME injection timing in hydrogen–DME PCCI combustion was also varied from −120 °CA to TDC, as in the DME PCCI engine operation. The total supplied heating value was fixed at 400 J for all cases. DME injection timing determined the start of combustion for the hydrogen–DME PCCI. With increasing the amount of hydrogen, exhaust emissions were reduced. Hydrogen–DME PCCI engine was operated with minimum amount of DME via the hydrogen addition and DME injection timing control. The optimized DME injection timing, −30 °CA aTDC, resulted in a lower exhaust emission-operation, while maintaining a higher IMEP.     

Numerical study of hydrogen addition to DME/CH4 dual fuel RCCI engine

In this study, the effect of hydrogen addition to DME/CH₄ dual-fuel RCCI (Reactivity Controlled Compression Ignition) engine is investigated using three dimensional calculations coupled with chemical kinetics. A new reduced DME (Dimethyl Ether) oxidation mechanism is proposed in this study. With the addition of H₂, the ignition time is advanced and the peak cylinder pressure is increased. The addition of hydrogen has a greater effect on the beginning stage of combustion than the later stages of combustion. The CH₄ emission is reduced with the addition of H₂. However, as the flame does not propagate throughout the charge, the CH₄ emission is still high. The CO emission is reduced and most of the remaining CO is produced by the combustion of the premixed CH₄. With the addition of hydrogen, NO emission is increased. The simulation shows that the final NOx emissions are significantly determined by the injection strategy and quantity of the pilot fuel during dual fuel operation conditions.     

Effect of injection parameters on the combustion and emission characteristics in a common-rail direct injection diesel engine fueled with waste cooking oil biodiesel

The objective of this paper was to study the effects of the injection pressure and injection timing on the combustion and emission characteristics in a single-cylinder common-rail direct injection (CRDI) diesel engine fueled with waste cooking oil (WCO) biodiesel and commercial diesel fuel. The fuel property including fatty acid composition for the biodiesel were measured and compared with those of the conventional diesel fuel. The engine tests were conducted at two injection pressures (80 and 160 MPa) and different injection timings from −25 to 0 crank angle degree (CAD) after top dead center (aTDC) under two different engine loads. The results showed that the indicated specific fuel consumption (ISFC) with respect to the injection timings of the biodiesel was higher than that of the diesel fuel under all experimental conditions. The peak cylinder pressure and the peak heat release rate of the biodiesel were slightly lower, while the ignition delay was slightly longer under all operating conditions. In terms of emissions, the biodiesel had benefits in reduction of smoke, carbon monoxide (CO), hydrocarbon (HC) emissions especially with high fuel injection pressure. The nitrogen oxide (NO_x) emissions of the biodiesel were relatively higher than those of the diesel under all experimental conditions.     

Dual-injection: The flexible,bi-fuel concept for spark-ignition engines fuelled with various gasoline and biofuel blends

Dual-injection strategies in spark-ignition engines allow the in-cylinder blending of two different fuels at any blend ratio, when simultaneously combining port fuel injection (PFI) and direct-injection (DI). Either fuel can be used as the main fuel, depending on the engine demand and the fuel availability. This paper presents the preliminary investigation of such a flexible, bi-fuel concept using a single cylinder spark-ignition research engine. Gasoline has been used as the PFI fuel, while various mass fractions of gasoline, ethanol and 2,5-dimethylfuran (DMF) have been used in DI. The control of the excess air ratio during the in-cylinder mixing of two different fuels was realized using the cross-over theory of the carbon monoxide and oxygen emissions concentrations. The dual-injection results showed how the volumetric air flow rate, total input energy and indicated mean effective pressure (IMEP) increases with deceasing PFI mass fraction, regardless of the DI fuel. The indicated efficiency increases when using any ethanol fraction in DI and results in higher combustion and fuel conversion efficiencies compared to gasoline. Increasing the DMF mass fraction in DI reduces the combustion duration more significantly than with increased fractions of ethanol or gasoline in DI. The hydrocarbon (HC), oxides of nitrogen (NO_x) and carbon dioxide (CO₂) emissions mostly reduce when using any gasoline or ethanol fraction in DI. When using DMF, the HC emissions reduce, but the NO_x and CO₂ emissions increase.