Stoichiometric H2ICE with water injection and exhaust and coolant heat recovery through organic Rankine cycles

High power density, stoichiometric, turbocharged, directly injected engines with water injection and a three way catalytic converter after treatment have been proposed as one of the most promising H₂ICE [1]. These throttle controlled engines have top brake efficiencies exceeding 40%, but large penalties in efficiency reducing the load with 1 bar BMEP values approaching 10%. Recovery of the large amount of fuel energy lost in the coolant especially at low loads as well as the fuel energy lost in the exhaust that is significant at high loads and speeds may push not only the top brake efficiencies to exceed the 45% mark, but also to dramatically increase the low load efficiency compromised by the throttling. In this paper, recovery of the waste heat from the exhaust gases and the coolant in a H₂ICE is performed with Organic Rankine Cycles (ORC). The engine without ORC has a maximum efficiency of 42% and an average efficiency over the map points of 32.7%. With the exhaust ORC, neglecting the possible back pressure increase due to the heat exchanger downstream of the catalytic converter the maximum efficiency increases to 45.6%, and the average efficiency rises to 35.3%. With the coolant ORC, neglecting the reduced mechanical efficiency for the coolant back pressure increment, the maximum efficiency increases to 43.4% and the average efficiency increases to 34.6%. Finally, combining the two ORC with same assumptions, the maximum efficiency increases to 46.9% and the average efficiency to 38%.     

Stoichiometric H2ICEs with water injection

For the most part, gasoline engines operate close to stoichiometry because of the high power density and the easy after treatment through the very well established three-way catalytic converter technology. The lean burn gasoline engine suffers major disadvantages for the after treatment still requiring aggressive research and development to meet future emission standards more than for the lower power density compensated by the better fuel conversion efficiency running lean. Hydrogen engines are usually run ultra-lean to avoid abnormal combustion phenomena and possibly to avoid the emission of nitrogen oxides without the difficult non-stoichiometric after treatment. While the ultra-lean combustion of hydrogen may reduce the formation of NOx within the cylinder but makes the power density very low, the only lean combustion of hydrogen requires after treatment for NOx reduction. The suppression of abnormal combustion in hydrogen engines has been a challenge for the three regimes of abnormal combustion, knock (auto ignition of the end gas region), pre-ignition (uncontrolled ignition induced by a hot spot prior of the spark ignition) and backfire (premature ignition during the intake stroke, which could be seen as an early form of pre-ignition). Direct injection and jet ignition coupled to port water injection are used here to avoid the occurrence of all these abnormal combustion phenomena as well as to control the temperature of gases to turbine in a turbocharged stoichiometric hydrogen engine.     

Multi-dimensional modeling of mixture preparation in a direct injection engine fueled with gaseous hydrogen

With the recent advances of direct injection (DI) technology, introducing hydrogen into the combustion chamber through DI is being considered as a viable approach to circumvent backfire and pre-ignition encountered in early generations of hydrogen engines. As part of a broader vision to develop a robust numerical model to study hydrogen spark ignition (SI) combustion in internal combustion (IC) engines, the present numerical investigation focuses on mixture preparation in a hydrogen DI SI engine. This study is carried out with a single hole injector with gaseous hydrogen injected at 100 bar injection pressure. Simulations are carried out for high and low tumble configurations and validated against optical data acquired from planar laser induced fluorescence (PLIF) measurements. Varying mesh configurations are investigated for the impact on in-cylinder mixture distribution. A particular emphasis is placed on the effect of nozzle geometry and mesh orientation near the wall. Overall, the computational model is found to predict the mixture distribution in the combustion cylinder reasonably well. The results showed that the alignment of mesh with the flow direction is important to achieve good agreement between numerical analysis and optical measurement data.     

Effects of direct water injection on engine performance in a hydrogen (H2)-fueled engine at varied amounts of injected water and water injection timing

In this paper, the effects of direct water injection (WI) on characteristics of combustion and emission for a hydrogen (H₂)-fueled spark ignition (SI) engine were experimentally investigated. The experiments conducted under different amounts of water injection (AWI) and varied water injection timing (WIT). The experimental results showed that in-cylinder pressure decreased, indicated thermal efficiency (ITE) increased, and the flame development (CA0-10) and propagation (CA10-90) periods prolonged when AWI raised. When AIW grew to 4.5 mg/cycle, Nitrogen oxides (NOx) expelled from the original engine decreased by 53.7% when excess air ratio (λ) was 1.15. Early WIT had positive effects on the reduction of NOx emissions. When WIT retarded, in-cylinder pressure increased, ITE decreased and CA0-10 and CA10-90 shortened, NOx emissions rapidly increased.     

Effect of water injection and spark timing on the nitric oxide emission and combustion parameters of a hydrogen fuelled spark ignition engine

One of the main problems with hydrogen fuelled internal combustion engines is the high NO level due to rapid combustion. Use of diluents with the charge and retardation of the spark ignition timing can reduce NO levels in Hydrogen fuelled engines. In this work a single cylinder hydrogen fuelled engine was run at different equivalence ratios at full throttle. NO levels were found to rise after an equivalence ratio of 0.55, maximum value was about 7500 ppm. High reductions in NO emission were not possible without a significant drop in thermal efficiency with retarded spark ignition timings. Drastic drop in NO levels to even as low as 2490 ppm were seen with water injection. In spite of the reduction in heat release rate (HRR) no loss in brake thermal efficiency (BTE) was observed. There was no significant influence on combustion stability or HC levels.     

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.     

Diagnosis and control of abnormal combustion of hydrogen internal combustion engine based on the hydrogen injection parameters

In order to improve the limitation of evaluating the abnormal combustion problem of hydrogen internal combustion engine by single index, the abnormal combustion risk coefficient is proposed and defined based on AHP(Analytic Hierarchy Process)-entropy method. The abnormal combustion risk of PFI hydrogen internal combustion engine is comprehensively evaluated from multiple indexes such as the uniformity coefficient of the mixture, the temperature of the hot area, the maximum temperature rise rate, the residual amount of hydrogen in the intake port and the cylinder temperature at the end of the exhaust. The influence of hydrogen injection parameters on abnormal combustion was explored. The results show that the temperature and the maximum temperature rise rate in the hot area decrease first and then increase with the increase of hydrogen injection angle and hydrogen injection flow rate. Although large hydrogen injection angle and hydrogen injection flow rate can reduce the cylinder temperature at the end of exhaust, they will increase the residual hydrogen amount in the intake port. Appropriate hydrogen injection angle and hydrogen injection flow scheme can ensure that all parameters are at a better level, so that the risk coefficient of abnormal combustion decreases by 2.1%–5.5%, and the possibility of abnormal combustion is reduced.     

Control of backfire and NOx emission reduction in a hydrogen fueled multi-cylinder spark ignition engine using cooled EGR and water injection strategies

The experimental study was carried out on a constant speed multi-cylinder spark ignition engine fueled with hydrogen. Exhaust gas recirculation (EGR) and water injection techniques were adopted to control combustion anomalies (backfire and knocking) and reduce NOx emission at source level. The experimental tests were conducted on the engine with varied EGR rate (0%–28% by volume) and water to hydrogen ratio (WHR) (0–9.25) at 15 kW load. It was observed from the experiments that both the strategies can control backfire effectively, but water injection can effectively control backfire compared to EGR. The water injection and EGR reduce the probability of backfire occurrence and its propagation due to the increase in the requirement of minimum ignition energy (MIE) of the charge, caused mainly due to charge dilution effect, and reduction in flame speed respectively. The NOx emission was continuously reduced with increase in EGR rate and WHR, but at higher rates (of EGR and WHR), there was an issue of stability of engine operation. It was found from the experimental results that at 25% EGR, there was 57% reduction in NOx emission without drop in brake thermal efficiency whereas, with WHR of 7.5, the NOx emission was reduced by 97% without affecting the efficiency. The salient point emerging from the study is that water injection technique can control backfire with ultra-low (near zero) NOx emission without compromising the performance of the hydrogen fueled spark ignition engine.     

Advantages of the direct injection of both diesel and hydrogen in dual fuel H2ICE

The turbocharged Diesel engine is the most efficient engine now in production for transport applications with full load brake engine thermal efficiencies up to 40-45% and reduced penalties in brake engine thermal efficiencies reducing the load. The secrets of the turbocharged Diesel engine performances are the high compression ratio and the lean bulk combustion mostly diffusion controlled in addition to the better use of the exhaust energy. Despite these advantages and the further complications of hydrogen in terms of abnormal combustion phenomena and displacement effect, the most part of the dual fuel Diesel-hydrogen engines has been developed so far injecting hydrogen in the intake manifold or in the intake port, and then injecting the Diesel fuel in the cylinder to ignite there a homogeneous mixture. This paper shows how a latest production common-rail Diesel engine could be modified replacing the Diesel injector by a double injector as those proposed by Westport since more than two decades for CNG first and then for CNG and hydrogen to provide much better performances. A model is first developed and validated versus extensive high quality dynamometer data for the Diesel engine only covering with almost 200 points the load and speed range. This model replaces the multiple injection strategy with a single equivalent injection for the purposes of the brake efficiency results still providing satisfactory accuracy. The model is then used to simulate the dual fuel operation with a pilot Diesel followed by a main hydrogen injection replacing the Diesel fuel with the hydrogen fuel and using the same parameters for start and duration of the equivalent injection at same percentage load and speed. While the top load air-to-fuel ratio of the Diesel is a lean 1.55, the top air-to-fuel ratio of the hydrogen is assumed to be a stoichiometric 1. Within the validity of these assumptions it is shown that the novel engine has better than Diesel fuel conversion efficiencies and higher than Diesel power outputs. These results clearly indicate the development of the direct injection system as the key factor where to focus research and development for this kind of engines.     

A novel hydrogen engine one litre two stroke delivering top power 110 kW and brake efficiency 36% within the 25 kg total weight constraints

The paper presents a novel design for a viable two stroke hydrogen engine that delivers excellent fuel economy and low emissions within the constraints of today's cost, weight and size. The engine features asymmetrical port timing through a translating and rotating piston mechanism. The engine is externally scavenged and supercharged, has wet sump and oil pressure lubrication, direct injection, it is lightweight, easy to build, with minimal number of parts, low production cost, ability to be balanced and compact design. The two stroke mechanism produces a linear motion of the pistons as well as an elliptical path on the surface of the cylinder. This allows the piston to sweep as well as travel past the ports. The piston has a raised lip around portion of its circumference that communicates with the inlet and exhaust ports through its sweep and linear motion that assist in creating the port's asymmetry to make the exhaust port to open first and to close first. The inlet port opens approximately 23° after the exhaust port opens, and remains open for some 20° after the exhaust port closes. The inlet port remains open to complete the cylinder charging and allow supercharging. The piston generates a perfect sinusoidal motion. Direct fuel injection and jet ignition are adopted for best results over a wide range of speeds and loads. The load is controlled by the quantity of fuel injected and changing the supercharger speed through a continuously variable transmission. This paper includes design details as well as result of engine performance simulations. The engine has better than traditional two stroke engines (1) top brake efficiency in the high 30% range and (2) range of speed and loads where the efficiency is above 30%.     

Stochastic reactor modelling of multi modes combustion with diesel direct injection or hydrogen jet ignition start of combustion

Recent papers 1, 2, 3, 4 and 5 have proposed two different systems to more efficiently and more rapidly burn the fuel in highly boosted, high compression ratio, directly injected internal combustion engines permitting multi-mode combustion operation. In a first system, a second direct injector is coupled with the standard Diesel direct injector and glow plug. The second direct injector introduces the most of the fuel while the Diesel direct injector only introduces a minimum amount of fuel to control the start of the combustion about top dead centre. The fuel injected before the Diesel ignition injection burns premixed, the fuel injected after the Diesel ignition injection burns diffusion. This design permits combustion premixed gasoline-like if all the fuel is injected before the Diesel ignition injection, diffusion Diesel-like if all the fuel is injected after the Diesel ignition injection (as done in the Westport High Pressure Direct Injection concept [12]), and mixed gasoline/Diesel like injecting the fuel before and after the Diesel ignition injection. The premixed gasoline-like mode is actually a homogeneous charge compression ignition (HCCI)-like mode, where an amount of fuel smaller than the threshold value producing top dead centre auto ignition is then ignited at top dead centre by the Diesel ignition injection in a more robust, stable and repeatable operation unaffected by small changes in properties and composition of the fuel and air mixture. In an alternative design, the glow plug is replaced by a jet ignition devices feed preferably with H₂. In this case, a spark ignition ignites the stoichiometric H₂-air mixture within the jet ignition pre-chamber. The jets of hot reacting H₂-air combusting gases then ignite the main chamber premixed mixture in the gasoline-like operation or create suitable conditions for the fuel subsequently injected to burn diffusion in the Diesel-like operation or perform both duties in the mixed gasoline/Diesel-like operation. A single main chamber direct injector is generally needed (for example with H₂, CH₄ or C₃H₈ fuels). With NH₃, a second main chamber direct injector with H₂ is also used to limit the volume of the jet ignition pre-chamber. In this short communications, the results of detailed chemistry simulations with the SRM (Stochastic Reactor Model) suite, a sophisticated engineering tool combining conventional 1D or 3D fluid dynamics approaches are presented to further support these two engine concepts working with fuels H₂, CH₄, C₃H₈, NH₃, I-C₈H₁₈ and N-C₇H₁₆ and adopting two different mechanisms for chemical kinetics. Within the limits of the present simulations (a very accurate chemical kinetic for combustion of I-C₈H₁₈ and N-C₇H₁₆ but a much less accurate chemical kinetic for the other fuels and especially for NH₃, unavailability of variable composition and variable properties multiple injections), the Diesel injection ignition and the hydrogen jet ignition are proved to permit combustion modes leading to indicated thermal efficiencies up to 10% better than the latest Diesels at high loads within the same peak pressure and peak temperature constraints.     

An experimental study of a direct injection compression ignition hydrogen engine

This paper describes the development of an experimental setup for the testing of a diesel engine in the direct injection hydrogen-fuelled mode. Test results showed that the use of hydrogen direct injection in a diesel engine gave a higher power to weight ratio when compared to conventional diesel-fuelled operation, with the peak power being approximately 14% higher. The use of inlet air heating was required for the hydrogen-fuelled engine to ensure satisfactory combustion, and a large increase in the peak in-cylinder gas pressure was observed. A significant efficiency advantage was found when using hydrogen as opposed to diesel fuel, with the hydrogen-fuelled engine achieving a fuel efficiency of approximately 43% compared to 28% in the conventional, diesel-fuelled mode. A reduction in nitrogen oxides emission formation of approximately 20% was further observed.     

Efficiency of hydrogen internal combustion engine combined with open steam Rankine cycle recovering water and waste heat

A hydrogen internal combustion engine (HICE) wastes more heat, and producing nearly three times more water than a conventional engine. This paper describes the principle behind a novel waste heat recovery sub-system that exploits the water produced by an HICE as the working fluid for an open-cycle power generation system based on the Rankine cycle. Water from the HICE exhaust is superheated by the waste heat from the HICE and used to produce power in a steam expander. A fundamental thermodynamic model shows the contribution of the sub-system to the overall thermal efficiency of the HICE at various engine speeds, with and without a condenser. The results show that the condenser is not cost-effective and that the overall thermal efficiency with the proposed sub-system is 27.2% to 33.6%, representing improvements of 2.9% to 3.7%, at engine speeds of 1500 to 4500 rpm.     

Numerical study on effects of hydrogen direct injection on hydrogen mixture distribution,combustion and emissions of a gasoline/hydrogen SI engine under lean burn condition

A numerical study on effects of hydrogen direct injection on hydrogen mixture distribution, combustion and emissions was presented for a gasoline/hydrogen SI engine. Under lean burn conditions, five different direct hydrogen injection timings were applied at low speeds and low loads on SI engines with direct hydrogen injection (HDI) and gasoline port injection. The results were showed as following: firstly, with the increase of hydrogen direct injection timing, the hydrogen concentration near the sparking plug first increases and then decreases, reaching the highest when hydrogen direct injection timing is 120°CA BTDC: Secondly, hydrogen can speed up the combustion rate. The main factor affecting the combustion rate and efficiency is the hydrogen concentration near the sparking plug: Thirdly, in comparing with gasoline, the NO_X emissions with hydrogen addition increase by an average of 115%. For different hydrogen direct injection timings, the NO_X emissions of 120°CA BTDC is the highest, which is 29.9% higher than the 75°CA BTDC. The hydrogen addition make the NO_X emissions increase in two ways. On the one hand, the average temperature with hydrogen addition is higher. On the other hand, the temperature with hydrogen addition is not homogeneous, which makes the peak of temperature much higher. In a word, the main factor of NO_X emissions is the size of high temperature zone in the cylinder: Finally, because the combustion is more complete, in comparing with gasoline, hydrogen addition can reduce the CO and HC emissions by 32.2% and 80.4% respectively. Since a more homogeneous hydrogen mixture distribution can influence a lager zone in the cylinder and reduce the wall quenching distance, these emissions decrease with the increase of hydrogen direct injection timing. The CO and HC emissions of 135°CA BTDC decrease by 41.5% and 71.4%, respectively, compared to 75°CA BTDC.     

Cycle variations in a hydrogen internal combustion engine

The cycle variation characteristics of a port fuel injection hydrogen internal combustion engine (PFI-HICE) have been extensively investigated. The covariance of indicated mean effective pressure (COV_imep) is the best parameter for evaluating the cycle variations in the PFI-HICE. COV_imep decreases as fuel–air ratio increases from 1000 to 5500 rpm, and engine speed minimally affects COV_imep. The effect of ignition advance angle on COV_imep is determined by fuel–air ratio. The ignition advance angles that correspond to the minimum COV_imep of the PFI-HICE decrease as fuel–air ratio increases. The effect of ignition advance angle on COV_imep diminishes as fuel–air ratio increases. The COV_imep of the PFI-HICE rapidly decreases as throttle increases when the throttle is less than 20%. Injection timing only slightly affects COV_imep under high-speed conditions, and COV_imep increases when hydrogen is injected in intake periods under low-speed conditions. These results indicate that studying COV_imep improves the stability of PFI-HICEs.     

Simulation of the combustion process for a CI hydrogen engine in an argon-oxygen atmosphere

Hydrogen combustion in a noble gas atmosphere increases the combustion chamber temperature, and the high specific heat ratio of the gas increases the thermal efficiency. In this study, nitrogen was replaced by argon as the intake air along with pure oxygen to supply the engine. The objectives of this study are to determine the effects of different engine parameters on combustion and to analyse the emissions from hydrogen combustion in an argon-oxygen atmosphere. This research was conducted through simulations using CONVERGE 2.2.0 software, and the YANMAR engine NF19SK model was used to determine the basic parameters. Changing the injector location affects the pressure and temperature in the combustion chamber. With increasing compression ratio, the pressure increases more rapidly than the temperature. However, combustion at high compression ratios decreases the maximum heat release rate and increases the combustion duration. Hydrogen combustion at ambient temperatures below 1200 K follows the Arrhenius equation.     

The characteristic of polytropic coefficient of compression stroke in hydrogen internal combustion engine

The polytropic coefficient has important effect on the calculation of the instantaneous heat release rate and its comparison with specific heat ratio contains the information of the gas-surroundings heat exchange. This article studies the polytropic coefficient characteristics from 1000 rpm to 5000 rpm and the equivalence ratio from 0.24 to 0.55 by using experimental data from a 2.0 L hydrogen engine. The polytropic coefficient increase from 1.3 to 1.35 with the increase of engine speed from 1000 rpm to 4000 rpm, and then it decrease to around 1.34. This characteristic can be used to calculate the heat release rate more accurately. The study of the effect of equivalence ratio suggested that the polytropic coefficient decreased with the increase of equivalence ratio. The polytropic coefficient of hydrogen engine ranges from 1.28 to 1.35, which is less than the gasoline of 1.32–1.4. And the rising period of polytropic coefficient of ‘hydrogen – 0.55’ at 4500 rpm is very longer than others, which showed that the gases properties had effect on the heat transfer. These characteristics could not only be used for heat transfer calculation, but they can also enrich the research of polytropic coefficient for hydrogen internal combustion engine.     

Backfire prediction in a manifold injection hydrogen internal combustion engine

Hydrogen internal combustion engine (H2ICE) easily occur inlet manifold backfire and other abnormal combustion phenomena because of the low ignition energy, wide flammability range and rapid combustion speed of hydrogen. In this paper, the effect of injection timing on mixture formation in a manifold injection H2ICE was studied in various engine speed and equivalence ratio by CFD simulation. It was concluded that H2ICE of manifold injection have an limited injection end timing in order to prevent backfire in the inlet manifold. Finally, the limit of injection end timing of the H2ICE was proposed and validated by engine experiment.