A Predictive Study of a New VCR Engine with High Expansion Ratio and High-Efficiency Potential under Heavy Load Conditions

Abstract

Facing the future, whether working alone or with electric motors, a new type of variable compression ratio (VCR) engine that can achieve a high thermal efficiency under heavy load conditions is necessary. Hence, we propose a dual shaft control variable compression ratio (DSC-VCR) engine based on a gear-driven eccentric sleeve. With the improved position of gears, DSC-VCR allows for double larger gears to share the load, and the engine can operate with a larger eccentric size and a narrower adjustment range compared to other similar mechanisms. This helps to reduce the difficulty of chamber shape design, avoid collisions between valves and piston, and above all, makes the engine operate with a larger overexpansion ratio (OER, the ratio of expansion stroke and compression stroke) under all conditions to improve engine efficiency. Based on a 1.5 T four-cylinder engine, the OER can be increased to over 1.16 with the eccentric size of 6.5 mm. According to the theoretical thermal efficiency calculation while considering turbocharging, the per millimeter increase of eccentric size improves the theoretical efficiency by 0.0025–0.006. The predictive simulation presented that the reduction of residual gas helps to increase the compression ratio (CR) from 9.5 to 10.1 under a full load condition. Larger OERs and CRs help to reduce brake specific fuel consumption (BSFC) by 6%–8%. In the case of a 75% load, about 3.51% of efficiency increase was realized. All of these prove that DSC-VCR is a high-efficiency potential mechanism for the future.

Improving the Efficiency of Spark-Ignition Internal Combustion Engine Using a Novel Electromagnetic Actuator and Adapting Increased Compression

“…Significant benefits have been demonstrated from these systems, resulting in a 7.5% reduction in fuel consumption. The research described in [10] also indicates a great potential for the use of variable compression ratio engines; it even indicates the potential to compete with electric motors used to drive passenger cars. For the tested engine, when the compression ratio was increased from 9.5 to 10.1, fuel consumption (FC) was reduced by 6-8%, and efficiency increased by 3.5% at 75% engine power load.…”

Study on selected parameters of engine with the active combustion chamber

“…Lin and Yang [28] proposed a dual shaft control variable compression ratio (DSC-VCR) engine based on a geardriven eccentric sleeve. This DSC-VCR allowed for double larger gears to share the load, and for the engine operation with a larger eccentric size and a narrower adjustment range than for the other similar mechanisms.…”

“…Therefore, during the tests, the speed value of 3500 rpm was adopted as a safe value. Using the base 1.5L four cylinder DVVT engine supplied with gasoline and the same engine with dual shaft control variable compression ratio (DSC-VCR) Lin et al [28] conducted comparative studies for the 3 cases: the maximum torque case with 1750 rpm (case 1), the maximum power case with 5500 rpm (case 2), and the high efficiency case with 2300 rpm and a 75% load (case 3). For the consecutive case numbers, the BSFC was equal to 260, 330 and 220 Nm, respectively.…”

“…When this value is exceeded, the torque starts to drop significantly, making the engine less efficient due to the falling in cylinder filling. For the comparison during mentioned studies using base 1.5 L four-cylinder DVVT engine supplied with gasoline and the same engine with dual shaft control variable compression ratio (DSC-VCR) [28] the engine torque was equal to 210, 190 and 155 Nm, for the case 1, case 2, and case 3, respectively. These values related to the consecutive values of the loaded engine torque to displacement ratio including 140, 126 and 103 Nm/L, respectively.…”

“…7 showed the full loaded engine torque to displacement ratio (engine torque related to one liter of displacement) in function of engine speed. Obtained values of such ratio did not exceeded value of 82 Nm/L.For the comparison during mentioned studies using base 1.5 L four-cylinder DVVT engine supplied with gasoline and the same engine with dual shaft control variable compression ratio (DSC-VCR)[28] the engine torque was equal to 210, 190 and 155 Nm, for the case 1, case 2, and case 3,…”