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Performance optimization of a small engine intake port has been studied through computational and experimental approach. Port angle, flange area and port shape are very important design parameters affecting performance of an intake port. Especially, radius of curvature of intake port inner surface has major effect on the flow coefficient of an intake port. As increasing port angle and flange area, flow coefficient is increased because pressure distribution and pressure gradient in the intake port are improved. Even though computational results over-predict maximum 8% compared with experimental result, they describe the tendency of flow coefficient according to the design parameters. Optimized intake port shows about 4.5% improved flow performance. Key Words : Intake Port, Small Engine, Flow Coefficient, Flow Simulation * 교신저자 : Sung-Young ParkTel: +82-10-5409-6450 e-mail: sungyoung@kongju.ac.kr접수일 11년 11월 29일 수정일 (1차 12년 02월 06일, 2차 12년 03월 02일) 게재확정일 12년 03월 08일

Since recently exhaust gas regulation for a non-road small engine as well as commercial vehicle engine has been enforced, a carburettor of a small engine should be replaced by an electronic fuel injection system. In this study, the spray characteristics of the 400cc gasoline small engine injector has been experimentally analyzed. Based on the experimental results, suitable injector for the small engine has been selected. Through the test rig measuring spray mass distribution, fuel distribution characteristics of 3 hole- and 6 hole-injector has been analyzed. Through the visualization equipment, injector spray angle, penetration length and spray width have been measured and analyzed. Considering spray characteristics and stability, 6 hole-injector is selected for the 400cc gasoline small engine.

One dimensional simulation model of an EFI small engine has been developed based on the commercial small engine. Newly developed simulation model has been evaluated comparing with the experimental results to check the validity. Simulation result shows very good agreement having margin of error of 3 percentage compared with experimental torque and power values. Also, to improve the small engine performance, the influence of the intake valve timing and duration on the engine performance has been analyzed using the simulation model.

The EFI small engine has been redesigned and manufactured based on a commercial small engine with a carburettor. Performance development of the EFI small engine has been conducted to optimize the operating conditions. Maximum torque and power were 12.56Ps and 25.4Nm, respectively, that were equivalent with carburettor type engine. Brake specific fuel consumption of the EFI small engine has been improved 17% on average compared with that of base small engine with a carburettor. By conducting KG2-6 mode test,HC+NOx was 7.46g/kWh that satisfied EPA Phase 3 regulation. THC has been reduced 41% on average, but NOx has been increased 3.5 times on average due to the improved thermal efficiency.

To develop gasoline engine fuel pump, it is needed to measure the rotational speed of the pump. In general, because gasoline fuel pump is submerged in the fuel tank, it is difficult to measure the rotational speed directly. Currently, there are two popular methods measuring the rotational speed. One of them is using a piezoelectric accelerometer, and the other is using a current sensor. Originally, a piezoelectric accelerometer had been applied to measure the frequency of the motor vibration. A current sensor is measuring current frequency of the commutator slot. In this study, both the piezoelectric accelerometer and the current sensor have been applied on the fuel pump to calculate the rotational speed at the same time. As a result, the current sensor delivered highly accurate rotational speed information compared with that of the piezoelectric accelerometer. Especially, low rotational speed region, the current sensor shows very robust measuring characteristics. To measure the rotational speed within 1% error, the piezoelectric accelerometer needs to be set with less then 0.5Hz datum storage interval, and the current sensor needs to be set with less then 2.0Hz datum storage interval.

Because of operating environment, the intake system of the small engine needs a serious design consideration. To capture oil particles from the blow-by gas, a grid of the intake system had been applied, but it has very low capturing efficiency and high manufacturing cost. To improve system performance, a new intake system has been developed using computational technique. The grid has been removed and the location of the blow-by hall has been re-designed. Total efficiency capturing oil particles has been improved about 5 times compared with that of previous model with the grid. By removing the grid, approximately 10% of the total manufacturing cast has been reduced. Key Words : Intake System, Small Engine, Engine Performance, Air Filter * 교신저자 : 박성영(sungyoung@kongju.ac.kr)접수일 09년 06월 24일 수정일 (1차 09년 10월 07일, 2차 09년 11월 04일) 게재확정일 09년 11월 12일 1. 서론 최근 들어 레져 및 이동의 편의성으로 인한 소형엔진의 사용이 보편화되고 있다. 소형엔진은 휴대 및 이동이 용이하도록 소형화 및 경량화가 주된 기술을 이루고 있으며, 저가의 기존기술을 사용하여 일상생활에 널리 보급되어 있다[1]. 공사 현장이나 실생활에서 널리 활용되는 소형엔진은 엔진이 운전되는 장소에서 먼지와 같은 이물질을 포함한 공기를 필수적으로 사용하게 된다. 따라서 엔진의 구동 및 운전 조건의 측면에서는 매우 열악한 환경에서 엔진이 작동되어야 한다. 이러한 소형엔진의 주 운전 조건을 고려해 볼 때 엔진으로 유입되는 흡입공기를 정화하는 흡기시스템은 엔진의 설계에서부터 고려되어야할 매우 중요한 설계인자이다[2]. 엔진의 흡기시스템은 연료의 연소를 위하여 엔진의 연소실에 공기를 공급하는 장치이다. 특히 소형엔진의 흡기시스템은 그 구조적인 단순화로 인하여 흡기필터를 포함한 흡기구가 엔진 흡기계의 대표적인 역할을 담당하고 있다. 소형엔진의 흡기 시스템은 공기의 흡입량에 직접적으로 관계되며, 흡입되는 공기는 연료의 분무성능에 영향을 미치게 된다.소형엔진의 흡기계 시스템은 케이스, 커버, 필터류 등으로 구성되며, 이들의 성능은 필터의 효율과 흡입되는 공기량에 따라 결정된다. 또한 흡기시스템에는 크랭크실로부터 유입되는 블로바이 가스에서 오일입자를 제거하는 장치가 설계되어있다. 이것은 그리드 또는 충돌판으로 구성되어 있다. 소형