Naturally Aspirated Research Articles

In-Cylinder Air Flow Characteristics Generated by Guide Vane Swirl and Tumble Device to Improve Air-Fuel Mixing in Diesel Engine Using Biodiesel

In order to improve a naturally aspirated (NA) Compression Ignition (CI) engine operating on biodiesel fuel, this research proposes a Guide Vane Swirl and Tumble Device (GVSTD) inside the intake runner of a HINO W04D diesel engine to improve the in-cylinder air flow characteristic as an alternative solution to supplement existing techniques. When the air intake was guided in front of the intake port, organized turbulent air was generated, consequently assisting the fuel to evaporate and mix to produce better combustion and eventually produce better performance. To examine the effectiveness of the GVSTD, a 3D IC engine simulation model was developed. Additionally, this paper also investigates the optimal vane height of GVSTD of four vanes which twist at 35° clockwise direction and are arranged perpendicular to each other with the length of the vanes three times that of the intake radius. Ten simulation models of the GVSTD, where the vane height varied from 10% to 100% of the intake radius were prepared. The simulation results of in-cylinder pressure, turbulence kinetic energy and velocity of the base and all GVSTD models were then compared. The results illustrate a promising improvement of the in-cylinder air flow characteristics inside the fuel injected region by utilizing 20% vane height compared to standard model.

Performance and emission characteristics of a SI engine fueled by low calorific biogas blended with hydrogen

In this study, an experimental investigation on a naturally aspirated (NA), 8-L spark ignition engine fueled by biogas with various methane concentrations – which we called the N 2 dilution test – was performed in terms of its thermal efficiency, combustion characteristics and emissions. The engine was operated at a constant engine rotational speed of 1800 rpm under a 60 kW power output condition and simulated biogas was employed to realize a wide range of changes in heating value and gas composition. The N 2 dilution test results show that an increase of inert gas in biogas was beneficial to thermal efficiency enhancement and NO x emission reduction, while exacerbating THC emissions and cyclic variations. Then, as a way to achieve stable combustion for the lowest quality biogas, H 2 addition tests were carried out in various excess air ratios. H 2 fractions ranging from 5 to 30% were blended to the biogas and the effects of hydrogen addition on engine behavior were evaluated. The engine test results indicated that the addition of hydrogen improved in-cylinder combustion characteristics, extending lean operating limit as well as reducing THC emissions while elevating NO x generation. In terms of efficiency, however, a competition between enhanced combustion stability and increased cooling energy loss was observed with a rise in H 2 concentration, maximizing engine efficiency at 5–10% H 2 concentration. Moreover, based on the peak efficiency operating point, a set of optimum operating conditions for minimum emissions with the least amount of efficiency loss was suggested in terms of excess air ratio, spark ignition timing, and hydrogen addition rate as one of the main results.

The effect of fuel properties on thermal efficiency of advanced spark-ignition engines

Owing to issues of global warming and energy security, improving engine thermal efficiency has become increasingly important today. This paper investigates the impact of high-research-octane-number (RON) fuels on engine thermal efficiency. It is shown that the lean boosted engine has higher potential to increase engine thermal efficiency than naturally aspirated (NA) engines and the combination of lean boosted engine and high-RON fuels gives around 44 per cent engine thermal efficiency. The engine thermal efficiency exceeds a diesel engine’s thermal efficiency. Therefore, the combination is expected to be an effective way to reduce CO2 emissions in the future. In this paper, the high-RON fuels are blended with gasoline components or bio-components. This paper also describes the combustion characteristics of ethanol and butanol. These fuels have good combustion features after the engine has warmed up. However, it is found that butanol gives more severe combustion characteristics under cold conditions.

Super clean diesel by usage of wide range, high boosted and cooled EGR system in single cylinder engine Japanese national project: super clean diesel engine

The heavy duty diesel engines have achieved status as prime movers for CO2 emissions. However, in the future heavy duty diesel engines will be required to have lower NOx and particulate matter (PM) emission levels than today. In this study high boost and lean diesel combustion has been attempted by a single cylinder engine in order to obtain a good engine performance and clean exhaust emission. The experiment has been done with intake air quantity up to five times of a naturally aspirated (NA) engine and 200MPa injection pressure. The adopted pressure booster is an external supercharger; and this experimental system can control the intake air temperature and also produce a high exhaust gas recirculation (EGR) rate in a wide speed and high load range.

Improvement of engine emissions with conventional diesel fuel and diesel–biodiesel blends

In this report combustion and exhaust emissions with neat diesel fuel and diesel–biodiesel blends have been investigated. In the investigation, firstly biodiesel from non-edible neem oil has been made by esterification. Biodiesel fuel (BDF) is chemically known as mono-alkyl fatty acid ester. It is renewable in nature and is derived from plant oils including vegetable oils. BDF is non-toxic, biodegradable, recycled resource and essentially free from sulfur and carcinogenic benzene. In the second phase of this investigation, experiment has been conducted with neat diesel fuel and diesel–biodiesel blends in a four stroke naturally aspirated (NA) direct injection (DI) diesel engine. Compared with conventional diesel fuel, diesel–biodiesel blends showed lower carbon monoxide (CO), and smoke emissions but higher oxides of nitrogen (NO x ) emission. However, compared with the diesel fuel, NO x emission with diesel–biodiesel blends was slightly reduced when EGR was applied.

Diesel Combustion and Emission Using High Boost and High Injection Pressure in a Single Cylinder Engine(Effects of Boost Pressure and Timing Retardation on Thermal Efficiency and Exhaust Emissions)

Heavy-duty diesel engines have adopted numerous technologies for clean emissions and low fuel consumption. Some are direct fuel injection combined with high injection pressure and adequate in-cylinder air motion, turbo-intercooler systems, and strong steel pistons. Using these technologies, diesel engines have achieved an extremely low CO 2 emission as a prime mover. However, heavy-duty diesel engines with even lower NOx and PM emission levels are anticipated. This study achieved high-boost and lean diesel combustion using a single cylinder engine that provides good engine performance and clean exhaust emission. The experiment was done under conditions of intake air quantity up to five times that of a naturally aspirated (NA) engine and 200 MPa injection pressure. The adopted pressure booster is an external supercharger that can control intake air temperature. In this engine, the maximum cylinder pressure was increased and new technologies were adopted, including a monotherm piston for endurance of P max = 30 MPa. Moreover, every engine part is newly designed. As the boost pressure increases, the rate of heat release resembles the injection rate and becomes sharper. The combustion and brake thermal efficiency are improved. This high boost and lean diesel combustion creates little smoke; ISCO and ISTHC without the ISNOx increase. It also yields good thermal efficiency.

Size analysis of automobile soot particles using field-flow fractionation.

Soot particles emitted from various automobile engines are analyzed for size distributions using field-flow fractionation (FFF). Soot samples are prepared for FFF analysis using a three-step procedure, where a layer of soot particles is focused between the layers of n-hexane and water, followed by dispersing of particles in water containing 0.05% Triton X-100. The mean diameters determined by FFF show similar trends with those obtained from dynamic light scattering (DLS) and scanning electron microscopy (SEM). Data from FFF are also compared with those from an on-line scanning mobility particle sizer (SMPS). SMPS size distributions extend further to larger size than those of FFF distributions, which indicates the three-step sample preparation procedure effectively disaggregates the agglomerated particles. Although the amount of particulate matter (PM) emitted from a heavy-duty diesel engine is much higher than that from a light-duty diesel engine, the size distributions of soot particles show no significant difference between heavy- and light-duty diesel engines. The engine-operating mode (engine speed and load rate) does not seem to affect significantly the size distribution of soot particles. It was found that the PM from a turbocharged diesel engine contains a higher percentage of particles smaller than 100 nm than an engine with a naturally aspirated (NA) air-inhalation system. As for gasoline engines, the PM collected after the catalytic converter has a narrower size distribution than those collected before and has a higher percentage of particles smaller than 100 nm.

Air Flow in a Naturally Aspirated Two-stroke Engine

The problem of scavenging of naturally aspirated, two-stroke cycle engines by utilization of wave effects in the exhaust and induction system is treated theoretically and investigated experimentally by systematic variation of the exhaust and induction system, as well as engine speed. In the theoretical treatment accuracy is achieved with a minimum of numerical computation by the adoption of the theory of waves of finite amplitude and the use of charts, wherever possible. These two features constitute the most significant departure from List's very thorough analysis (List 1949/50)‡, which is based throughout on the small-wave theory and in which little attention appears to have been paid to the simplification of numerical work. The theoretical section is divided into two parts dealing with (1) the analysis of cyclical pressure fluctuations in the engine cylinder and pipe system, and (2) the treatment of the gas-exchange process in the cylinder on the basis of ‘perfect mixing’ and the derivation of the conditions for dynamic similarity. A novel experimental technique is used, air from an external compressor being admitted to the cylinder of the motored engine through a rotary valve. In this manner release pressures comparable with those obtaining in the firing engine are attained, while the effects of high temperatures, which are of secondary importance in relation to wave phenomena, are eliminated. The experimental work is divided into two parts: (1) tests corroborating the wave theory; and (2) systematic air-consumption trials with variable induction-pipe lengths and exhaust systems, incorporating ( a) plain pipes, ( b) an exhaust ejector similar to that described in the Kadenacy patent specifications, ( c) an expansion chamber, and ( d) a diffuser. The general conclusions are: (1) good agreement between observations and analytical results is obtained, (2) high air-consumption is possible with natural aspiration provided that effective use is made of wave action by correctly designed exhaust and inlet systems; and (3) satisfactory scavenging is only achieved if not only the external pipe system but also the engine speed and geometry conform to certain requirements conveniently expressed in the form of dimensionless groups.