Baseline Evaluation of Ignition Timing and Compression Ratio Configurations on Efficiency and Combustion Stability of a Small-Bore, Two-Stroke, Natural Gas Engine

Abstract

Two-stroke engines continue to dominate the small engine market based on cost and simplicity, though companies have incorporated small four-stroke engines into handheld equipment. On the other end of the displacement spectrum, two-stroke natural gas engines are common in large-bore applications within the natural gas compression industry. Nearly 60% of homes utilize natural gas and could therefore benefit from its use as fuel for decentralized power generation. Such use for home applications does not require significant investment in infrastructure, which has limited its penetration into the transportation sector. Companies already offer back-up power generation systems for home use fueled by either natural gas or propane. These systems are often cost prohibitive and rely on four-stroke engines. The ultimate goal is to apply advanced technologies, such as direct fuel injection, to improve efficiency of small two-stroke engines. To establish a baseline, researchers developed a micro-engine test facility to examine effects of ignition timing, compression ratio, and intake and exhaust systems on efficiency and combustion stability. This research focuses on an air-cooled, spark-ignited, two-stroke engine converted to operate on natural gas. In addition to fuel conversion, an electronic ignition system replaced the stock magneto driven coil. The added trigger wheel provided a signal for control of ignition and injection timing, and for in-cylinder pressure time alignment. Engine displacement was 29-cc with a bore and stroke of 35 mm and 30 mm. Tests were performed on gasoline and a natural gas blend at an engine speed of 5400 RPM. Fuel flow was adjusted for each case to produce maximum brake torque. Two different fuel delivery methods were tested for natural gas — a mass flow controller and an electronic port fuel injector. Tests examined the effects of two compression ratios for spark timings of 15, 20, 25, and 30 CAD BTDC. Fumigation and port injection decreased efficiency compared to gasoline by 24 and 32%, respectively. Brake power also decreased by 64 and 65% on average. A similar trend occurred for delivery ratio due to the volume of fresh air displaced by natural gas. Delivery ratio of fumigation and port injection decreased compared to gasoline by 12 and 27%, respectively. The coefficient of variation in indicated mean effective pressure varied from six to 27% over compression ratio and ignition timing sweeps.

Weak Knock Characteristic Extraction of a Two-Stroke Spark Ignition UAV Engine Burning RP-3 Kerosene Fuel Based on Intrinsic Modal Functions Energy Method

“…It is generally accepted that knock is caused by the auto-ignition of the end-gas [10]. In the combustion chamber of SI engines, the flame front propagates from the ignition source (around the spark plug) to the end-gas [11,12]. The temperature and pressure of the end-gas increase during the propagation of the flame, and if the temperature becomes too high, the end-gas may ignite spontaneous, which results in knock combustion [13][14][15].…”

Development of Resonating Oscillating Linear Engine Alternator; Instrumentation and Control

“…If the displacement is lower than the stroke length is lower than the stroke length of the engine, the pressure will be lower than the required compression value and the combustion might not occur. There the ignition pulse should happen near to the TDC to produce maximum output power [52].…”

Experimental Design, Testing, and Evaluation of Methods to Improve the Efficiency and Reduce Emissions from a Small Two-stroke Natural Gas Engine

“…In the case of CCC engines that use reeds, this occurs prior to the reed valve which enters the crankcase. As a result of early mixing, the air fuel mixture becomes homogenous within the crankcase [42]. For gaseous fuel, PI and fumigated fueling have similar power, efficiency, and DR for this reason [42].…”

“…The FTIR measured both NO and NO2 separately, from which the sum formed the NOx concentration as shown in Equation (42). The CO2 equivalent was determined from the combination of brake specific CO2 and a weighting factor multiplied by brake specific CH4 as shown in Equation (42). Brake specific NMHC is determined from the subtraction of methane from THC in Equation (43 proportionally NMHC increased.…”