Direct Injection Stratified Charge Research Articles

Impact of coolant temperature on piston wall-wetting and smoke generation in a stratified-charge DISI engine operated on E30 fuel

A late-injection strategy is typically adopted in stratified-charge direct injection spark ignition (DISI) engines to improve combustion stability for lean operation, but this may induce wall wetting on the piston surface and result in high soot emissions. E30 fuel, i.e., gasoline with 30% ethanol, is a potential alternative fuel that can offer a high Research Octane Number. However, the relatively high ethanol content increases the heat of vaporization, potentially exacerbating wall-wetting issues in DISI engines. In this study, the Refractive Index Matching (RIM) technique is used to measure fuel wall films in the piston bowl. The RIM implementation uses a novel LED illumination, integrated in the piston assembly and providing side illumination of the piston-bowl window. This RIM diagnostics in combination with high-speed imaging was used to investigate the impact of coolant temperature on the characteristics of wall wetting and combustion in an optical DISI engine fueled with E30. The experiments reveal that the smoke emissions increase drastically from 0.068 FSN to 1.14 FSN when the coolant temperature is reduced from 90 °C to 45 °C. Consistent with this finding, natural flame luminosity imaging reveals elevated soot incandescence with a reduction of the coolant temperature, indicative of pool fires. The RIM diagnostics show that a lower coolant temperature also leads to increased fuel film thickness, area, and volume, explaining the onset of pool fires and smoke.

Numerical investigation of direct injection stratified charge combustion in a natural gas-diesel rotary engine

To further improve the performance of diesel rotary engine, a novel natural gas-diesel rotary engine was proposed and studied in this paper. Based on a spray experimental setup, the diesel spray characteristics under diesel rotary engine working conditions were obtained and analyzed. Thereafter it was used to validate the spray model for diesel rotary engine modeling and simulation. The effect of different natural gas blending ratios on mixture formation and combustion process in the natural gas-diesel rotary engine were investigated. Simulation results showed that for fuel-air mixing process, the natural gas movement process was susceptible to the airflow motion. However, the diesel distribution range was obviously enlarged under the influence of high-speed unidirectional flow. At assisted ignition timing, the stratified distributed diesel made the combustion process mainly occured at the front and middle of the combustion chamber. Besides, the flame propagation speed was accelerated with natural gas blending ratio increasing, which effectively improved the total combustion rate. Compared to single-fuel mode, when natural gas blending ratio increased to 20%, the maximum combustion pressure increased by 24.17%. Meanwhile, soot and CO decreased obviously, but NO and CO2 also increased.

Numerical study of formaldehyde and unburned methanol emissions of direct injection spark ignition methanol engine under cold start and steady state operating conditions

The effects of overall equivalence ratio, injection timing, and ignition timing on formaldehyde and unburned methanol emissions, cylinder temperature histories, and formaldehyde emission histories of a spark ignition direct injection stratified charge methanol engine during cold start and steady state conditions were simulated using computational fluid dynamics coupling the methanol chemical kinetics reaction mechanism. The model results show that the overall equivalence ratio is less than 0.43, and unburned methanol significantly higher for cold start mode. For steady state mode, when the overall equivalence ratio is less than 0.4, formaldehyde and unburned methanol emissions increase rapidly. When the overall equivalence ratio is larger than 0.4, formaldehyde and unburned methanol emissions are very low. Formaldehyde and unburned methanol emissions for steady state mode are significantly lower than for cold start mode. For steady state mode at engine speed 1600rpm and brake mean effective pressure 0.67MPa formaldehyde and unburned methanol emissions are reduced 90% and 98%, respectively, compared to cold start mode at the same overall equivalence ratio (0.5). Cylinder temperature is the main factor that affects formaldehyde generation and consumption. There is a rapid decrease due to oxidation at the corresponding position of the maximum cylinder temperature, after which formaldehyde is quickly generated for any operating conditions.

Combined effects of flow/spray interactions and EGR on combustion variability for a stratified DISI engine

This study investigates combustion variability of a stratified-charge direct-injection spark ignited (DISI) engine, operated with near-TDC injection of E70 fuel and a spark timing that occurs during the early part of the fuel injection. Using EGR, low engine-out NOx can be achieved, but at the expense of increased combustion variability at higher engine speeds. Initial motored tests at different speeds reveal that the in-cylinder gas flow becomes sufficiently strong at 2000rpm to cause significant cycle-to-cycle variations of the spray penetration. Hence, the fired tests focus on operation at 2000rpm with N2 dilution ([O2]=19% and 21%) to simulate EGR. In-cylinder flow, spray, and early-flame measurements are correlated to reveal their effect on the combustion variability.Results reveal two types of flow/spray-interactions that predict the likelihood of a partial burn. (1) Proper flow direction before injection with a more collapsed spray leads to high kinetic energy of the flow during injection, thus generating a rapid early burn, which ensures complete combustion, regardless of the EGR level. (2) Improper flow direction and less collapsed spray generate low flow energy during the early phase of combustion. For this second type of flow/spray-interaction, application of EGR results in a partial-burn frequency of 30%, whereas without EGR, early combustion is shown to be insensitive to flow variations. Flame-probability maps illustrate that the partial-burn cycles for operation with EGR have a weak flame development in that the flame does not develop uniformly and reliably from the spark plug. Without EGR, the flame development is more repeatable regardless of the type of flow/spray-interaction, at the expense of higher NOx emissions.

Increasing energy efficiency of a gasoline direct injection engine through optimal synchronization of single or double injection strategies

The greatest fuel efficiency advantages of gasoline direct injection (GDI) engines are achieved under the so-called mixed mode boosting, where mixture characteristics are properly adapted to the specific working condition. In particular, in the medium range of load and speed, overall lean mixtures are suitable of being used in the so-called direct injection stratified charge operation.Present paper reports the results of numerical optimization analyses aimed at increasing the energetic efficiency of a GDI engine equipped with a high pressure multi-hole injector under both single and double injection events. In moderate-load moderate-speed lean conditions, the single or double injection synchronization in the working cycle is effected through a procedure that couples a 3D numerical model of the in-cylinder processes with an optimization tool. The choice of both the start of the injection events and the time of spark advance is realized to maximize the engine work.The optimal double injection solution is shown to increase the engine energy efficiency with respect to the case injection is realized in one shot, thus confirming that split injections improve the quality of the charge stratification under lean operation. The effect on the major pollutants is also discussed.

Comparison of performance of a Greener direct-injection stratified-charge (DISC) engine with a spark-ignition engine using a simplified model

The direct-injection stratified charge (DISC) engine is a hybrid between spark ignition (SI) and compression-ignition engines, it combines many of the best features of both with some unique advantages of its own. This includes multi-fuel capability, high thermal efficiency, low NOx production, and low particulate emissions.This work shows how simple semi-global models can predict the performance of the SI and DISC engines with reasonable accuracy, without going to details of modeling for internal processes such as: swirl, mixing and detailed combustion kinetics.The operating variables studied were inlet manifold pressure p i, exhaust manifold pressure p e, engine speed N, equivalence ratio Φ, and volumetric efficiency η v at different loads. The corresponding performance parameters were the brake mean effective pressure bmep, brake power P b, and brake thermal efficiency η b,th. The main contribution of this work is the production of friendly set of curve-fitting correlations for engine performance. The bmep and the P b increase with the load for both engines. For spark ignition engines the bmep increases by about 70% when load increases from 50% to 100%. With the DISC engine, this ratio increases to 75%. The percent improvement in η b,th for the DISC to the SI engine is around 50% which increases with part load, lower compression ratio r c and p i.

Effect of injection and ignition timings on performance and emissions from a spark-ignition engine fueled with methanol

Optimal injection and ignition timings and the effects of injection and ignition timings on performance and emissions from a high-compression direct-injection stratified charge spark-ignition methanol engine have been investigated experimentally. The results have shown that direct-injection spark-ignition methanol engine, in which a non-uniform mixture with a stratified distribution can be formed, has optimal injection and ignition timings to obtain a good combustion and low exhaust emissions in the overall mode range. Both methanol injection timing and ignition timing have a significant effect on methanol engine performance, combustion, and exhaust emissions. At an engine speed of 1600 rpm, full load, and optimal injection and ignition timings, methanol engine can obtain shorter ignition delay, lesser cycle-by-cycle variation, the maximum in-cylinder pressure, the maximum heat release rate, and higher thermal efficiency compared to the case of non-optimized injection and ignition timings. For methanol engine, the optimization of injection timing and ignition timing can lead to an improvement of brake-specific fuel consumption of more than 10% compared to non-optimized case in the overall load range and engine speed of 1600 rpm. The best compromise between thermal efficiency and exhaust emissions is reached at optimal injection and ignition timings.

Mixture distribution measurement using laser induced breakdown spectroscopy in hydrogen direct injection stratified charge

Reduction in cooling loss due to the heat transfer from burning gas to the combustion chamber wall is very important for improving the thermal efficiency in hydrogen engines. The previous research has shown that the direct injection stratified charge can be a technique to reduce the cooling loss and improve thermal efficiency in hydrogen combustion. For effective reductions in cooling loss by the stratified charge, it is very important to know the relation between the fuel injection conditions and mixture distribution. The current research employs the laser induced breakdown spectroscopy as a method to measure the hydrogen concentration distribution in the direct injection stratified charge. Measurement of instantaneous local equivalence ratio by the method clears the characteristics of mixture formation in hydrogen direct injection stratified charge. This research also tries to actively control the mixture distribution using a split fuel injection.

Development of a direct-injection stratified-charge methanol engine

On the basis of the wall-guided, spray-guided, and air-guided technologies related to gasoline direct-injection spark-ignition (DISI) engines, a complex-guided stratified-charge combustion system for a methanol DISI engine was developed. The test engine was a retrofitted four-cylinder diesel engine. The key parameters were optimized numerically and experimentally, such as the location of the swirl deflector, the spatial location of spray, the swirl ratio, the injection and ignition timings, and the needle valve opening pressure. The results show that the direct-injection stratified-charge (DISC) methanol engine can work with an excessive air ratio λ as high as 2.23, and its brake thermal efficiency reaches 29.7 per cent at a speed of 1500r/min, and a brake mean effective pressure of 0.45MPa. The DISC methanol engine exhibits relatively good performance with little cyclic variations, although it is sensitive to induction swirl. The test results indicate that the matching principle is successful. The developed DISC methanol engine can run under variable induction swirl to meet the requirement of stratification combustion under different engine speed operating conditions.

Suboptimal Control of Switched Systems With an Application to the DISC Engine

The growing stringency of fuel economy, emissions, and drivability requirements has led to proliferation of powertrain systems that have multiple discrete operating modes. Systematic approaches to the development of optimal and robust control systems for such powertrains are needed to contain their increased development times and costs. In this paper, we propose a new approach for controlling switched systems that is applicable to powertrain systems with multiple operating modes. Our approach reduces the complexity of computing a control law to a linear programming problem defined over a finite number of states in each operating mode. The methodology is designed to be suitable for practical applications while, under appropriate conditions, providing near-optimal performance. An application to the direct injection stratified charge engine with two distinct operating modes is given to illustrate our approach.

Measures to Overcome Low-Load Misfiring of 2-Stroke Cycle Spark Ignition Engine by Direct Injection Stratified Charge Combustion

2-stroke cycle spark ignition engine with direct injection was studied to avoid inherent misfiring in low load region by using stratified charge combustion. The three mixture formation concepts of spray-guided, wall-guided and air-guided were introduced to achieve stratified charge combustion and the stable combustion was obtained in three concepts. The most stable ignitability was achieved by spray-guided concept and the second was wall-guided concept. In the case of air-guided concept stable combustion was obtained with swirl motion that was generated by the closure of half part of scavenging port. Decreasing delivery ratio within no smoke and stable combustion regions was found to cause the reduction of NOx emission.

Improving thermal efficiency by reducing cooling losses in hydrogen combustion engines

Hydrogen can be readily used in spark ignition engines as a clean alternative to fossil fuels. However, the higher burning velocity and shorter quenching distance of hydrogen compared with hydrocarbons cause a larger heat transfer from the burning gas to the combustion chamber walls. Because of this cooling loss, the thermal efficiency of hydrogen-fueled engines is sometimes lower than that of conventionally fueled engines. Therefore, reducing the cooling loss is a crucial element in improving the thermal efficiency of hydrogen combustion engines. Previous research by the author and others has proposed the direct injection stratified charge as a technique for reducing the cooling loss in hydrogen combustion and shown its effect in reducing cooling loss through experiments in a constant volume combustion vessel. However, it is known that a reduction in cooling loss does not always improve thermal efficiency due to a simultaneous increase in the exhaust heat loss. This paper explains the relation between cooling loss reduction and thermal efficiency improvements by the direct injection stratified charge in hydrogen combustion engines.

Hybrid Model Predictive Control of Direct Injection Stratified Charge Engines

This paper illustrates the application of hybrid modeling and model predictive control techniques to the management of air-to-fuel ratio and torque in advanced technology gasoline direct-injection stratified-charge (DISC) engines. A DISC engine is an example of a constrained hybrid dynamical system, because it can operate in two distinct modes (stratified and homogeneous) and because the mode-dependent constraints on the air-to-fuel ratio and on the spark timing need to be enforced during its operation to avoid misfire, knock, and high combustion variability. In this paper, we approximate the DISC engine dynamics as a two-mode discrete-time switched affine system. Using this approximation, we tune a hybrid model predictive controller with integral action based on online mixed-integer quadratic optimization, and show the effectiveness of the approach through simulations. Then, using an offline multiparametric optimization procedure, we convert the controller into an equivalent explicit piecewise affine form that is easily implementable in an automotive microcontroller through a lookup table of linear gains

A study of mixture formation processes in direct injection stratified charge gasoline engines by quantitative laser-induced fluorescence imaging and the infrared absorption method

Mixture formation processes were investigated of three types of direct injection stratified charge gasoline engine based on wall-guided, air-guided, and spray-guided concepts. Temporal and spatial variations of fuel concentration in the combustion chamber were measured by laser diagnostics such as quantitative laser-induced fluorescence (LIF) imaging and infrared absorption methods on a single-cylinder optical engine. It was found from the experiments that the direct injection gasoline engines based on both the wall-guided and air-guided concepts have long time intervals between the end of injection timing and ignition timing, and this demands early injection and ignition timings in the compression stroke, resulting in lower thermal efficiencies than those of the spray-guided concept. As for the spray-guided concept, fuel is ignited immediately after the end of injection, which enables near TDC (top dead centre) combustion, allowing lower fuel consumption than the other two. However, the condition for stable ignition and combustion achieved with the spray-guided concept is very narrow in terms of injection and ignition timings, so it is essential to widen the condition in order to make the concept a reality.

Effect of the Ratio between the Connecting-Rod Length and the Crank Radius on Thermal Efficiency

In reciprocating internal combustion engines, Otto cycle indicates the best thermal efficiency under the same compression ratio among ideal cycles. To achieve this, combustion must take place instantaneously at top dead center, but it is actually impossible. Meanwhile, if a slower piston motion around top dead center was allowed, both the in-cylinder pressure and degree of constant volume would increase, leading to higher thermal efficiency. In order to verify this idea, an engine with a slow piston motion by adopting a large ratio between the connecting-rod length and the crank radius was tested. As expected, while degree of constant volume was increased, thermal efficiency was not improved due to increased heat loss. Further experiments were carried out using a direct injection stratified charge combustion system which allows selective reduction of heat loss, and high thermal efficiency was attained. On the contrary, an engine with a faster piston motion by adopting a smaller ratio between the connecting-rod length and the crank radius attained high thermal efficiency under the quick burn pre-mixed spark ignition combustion.

3122 DISC-HCCIハイブリッド燃焼エンジンの特性(S46-2 着火と燃焼の応用,S46 着火と燃焼)

An engine with DISC-HCCI hybrid combustion was designed to study the improvement of thermal efficiency in gasoline engines. The engine had both Direct Injection Stratified Charge (DISC) cylinder and Homogeneous Charge Compression Ignition (HCCI) cylinder simultaneously. The DISC cylinder was operated under Lean Burn, and then the exhaust gas was lead to the HCCI cylinder directly. Hence, it was possible for the HCCI cylinder to be operated under compression ignition easily by the high temperature exhaust gas with the left oxygen from the DISC cylinder. In this paper, the basic characteristics of the engine with DISC-HCCI hybrid combustion are described.

Flame inertia into lean region in stratified hydrogen mixture

In hydrogen engines, the direct-injection stratified charge system has the ability to realize a more lean operation than homogeneous charge systems. Flame propagation into the lean region in the stratified hydrogen mixture was investigated in this study. Hydrogen was injected into a lean hydrogen–air premixed mixture charge of the equivalence ratio of 0.074–0.257. This stratified hydrogen mixture was ignited by an electric spark. The flame generated in the hydrogen jet propagated into the lean premixed mixture charge as if it had “inertia”, even though the stoichiometry of the premixed mixture charge was less than the lower flammability limit. The amount of burned hydrogen in the case of a stratified mixture was greater than that in the case of the homogeneous mixture. The flame seems to be supported from behind by the burned gas in the rich region until the decay of this support.

Reduction of Cooling Loss in Hydrogen Combustionby Direct Injection Stratified Charge

Reduction of cooling loss from burning gas to the wall is crucial for improving thermal efficiency in hydrogen combustion engines. The research proposes the direct injection stratified charge to reduce the cooling loss in hydrogen combustion and analyzes its characteristics. The stratified charge in this research adopts direct fuel injection into lean mixture and spark ignition. The stratification is controlled by a fraction of directly injected fuel to the totally supplied fuel. A lowered temperature of the burning gas around the combustion chamber wall due to the leaner mixture by the stratification is expected to effectively reduce the heat transfer. The characteristics are analyzed in a constant volume combustion vessel by using measured pressure data and combustion gas compositions. Flame propagation is also observed for some cases.

Improvement of Stratified Combustion by a Large Amount of Hot EGR (Reduction of Unburned Hydrocarbons)

Unburned hydrocarbons from a direct injection stratified charge engine were greatly reduced by a large amount of hot EGR. A hydraulically controlled variable valve system was used to realize the hot EGR. Almost all the amount of required EGR gas for the NOx reduction was supplied directly from the previous cycle through the exhaust or inlet valves. Two kinds of recirculation were examined in this test. The first was the recirculation through the exhaust valves, which opened additionally during the suction stroke. Another was the recirculation through the inlet valves. The exhaust gas was pushed back to the port during the exhaust stroke through the additionally opened inlet valves and re-induced in the next cycle. Although both methods have the same ability to reduce HC emissions, required EGR was less in the latter method.

Analysis of Turbulent Combustion in Simplified Stratified Charge Conditions.

The stratified charge combustion system has been widely studied due to the significant potentials for low fuel consumption rate and low exhaust gas emissions. The fuel-air mixture formation process in a direct-injection stratified charge engine is influenced by various parameters, such as atomization, evaporation, and in-cylinder gas motion at high temperature and high pressure conditions. It is difficult to observe the in-cylinder phenomena in such conditions and also challenging to analyze the following stratified charge combustion. Therefore, the combustion phenomena in simplified stratified charge conditions aiming to analyze the fundamental stratified charge combustion are examined. That is, an experimental apparatus which can control the mixture distribution and the gas motion at ignition timing was developed, and the effects of turbulence intensity, mixture concentration distribution, and mixture composition on stratified charge combustion were examined. As a result, the effects of fuel, charge stratification, and turbulence on combustion characteristics were clarified.