# Advances in Diesel-LNG Internal Combustion Engines
## 2 Results
### 2F Diesel-LNG ICEs R&D
To aid with ignition, a small amount of diesel fuel is injected into the ICE followed by the main NG injection. Westport HPDI replaces approximately 92% of the diesel fuel (by energy) with NG. The Westport HPDI technology was developed for diesel and LNG to replace the main injection of the diesel with a more environmentally friendly fuel, NG, delivered liquefied. The Westport HPDI system for diesel and LNG is well established by decades [24; 25; 45; 46]. It may be regarded as an innovation relevant to transport not less than turbocharging and the Unijet for the diesel. The Westport HPDI technology uses NG as the primary fuel along with a small amount of diesel as a pilot ignition source, or \"liquid spark plug\". The ICE uses a revolutionary injector with a dual-concentric needle design allowing DI of small quantities of diesel and copious quantities of LNG. The LNG is injected at the end of the compression stroke, after the diesel pilot, and it burns diffusion controlled. The Westport HPDI [25] is an integrated system offered for new trucks or conversion of existing diesel trucks permitting operation with NG for reduced fuel costs, reduced CO\({}_{2}\) emissions, reduced soot emissions, and diesel-like performance. The Westport HPDI offers the same power, torque, engine braking and drivability of the diesel. The Westport HPDI also allows inherently low engine-out emissions of unburnt methane. Westport HPDI consists of a cryogenic tank, an HP LNG, HP fuel rails, and a dual concentric needle injector. This injector allows independent delivery of small quantities of diesel fuel for pre/pilot injections and massive quantities of NG as the main injection, both at relatively HP, directly to the combustion chamber. The NG is injected at the end of the compression stroke after the diesel, and it burns diffusion controlled. Further developments are being considered for this basic concept. The Westport HPDI system for diesel and CNG/LNG is a technology well established over the last three decades [45; 46]. This technology has been further evolved from a simple main injection of NG following the pilot/pre diesel injection, to more complex strategies that include premixed and diffusion combustion of the NG, as it was suggested in [47]. Traditional HPDI of LNG in HDT ICEs allows an NG ICE to maintain diesel-like performance while using to a major extent the fuel energy of the NG. The small diesel pilot injection accounts for 5-10% of the fuel energy. It is used to ignite the DI LNG. The NG burns in a mixing-controlled, or diffusion, combustion mode, depending on being injected prior or after the pilot diesel. Increased pressure, 600-bar 2F injectors for the LNG and the diesel are reported in [48]. The LNG combustion event is limited by the injection pressure. The injection pressure dictates the rate of mixing, and thus the combustion rate. By increasing the injection pressure from the traditional 300-bar to 600-bar, significant efficiency improvements and PM reductions are achieved at high loads, and especially at higher speeds. As a collateral effect, because pressure build-up and combustion rate are linked together, increases in combustion noise and harshness are drawbacks of the larger injection rates and the faster combustion allowed by the higher injection pressure. As mitigation strategies, a reduction of the diameter of the LNG nozzle holes may help to control the fuel injection rate and the combustion rate. Higher pressures driven faster combustion improves efficiency, with benefits of about 3%. Additionally, PM reductions are of the order of 40-60%. Reference [49] used a prototype fuel injector nozzle. Seven individual equally spaced gas injection holes are replaced by seven pairs of closely-aligned holes (\"paired-hole nozzle\" in [49]). The paired hole nozzle is intended to reduce PM formation by increasing the air entrainment due to the interaction with the jet. Opposite to the expectations, CO and PM emissions increased. They were three to 10 times higher when using the paired hole nozzles.